Saturday, January 30, 2010

Cardiomegaly Case 4

Cardiomegaly Case 4

A 40-year-old man presents to the emergency department complaining of severe shortness of breath. The breathlessness has been worsening over the past few years, and the patient reports growing tachypneic with mild exertion, and sometimes even at night. On examination, he has generalized edema, jugular venous distention, and hepatic distention. Cardiac examination shows a right ventricular heave, a right-sided S3, and S4 with a pulmonary ejection click. A chest x-ray film shows cardiomegaly and widening of the hilar vessels, including the pulmonary arteries. An electrocardiogram shows talI, peaked P waves in leads lI, III, and aVF, right axis deviation, and right ventricular hypertrophy.

Q 1
Which of the following is the most likely diagnosis?
/ A. Cor pulmonale
/ B. Hypertrophic cardiomyopathy
/ C. Left ventricular failure
/ D. Myocardial infarction
/ E. Pulmonary embolus (acute)

Q 2
Pulmonary hypertension is suspected in the patient, and a Swan-Ganz catheter is placed. Which of the following denotes the correct
anatomic sequence of vessels that would be traversed by the catheter if it was introduced into the left subclavian vein?
/ A. Left subclavian vein, Ieft brachiocephalic vein, superior vena cava, right atrium, right ventricle, pulmonary artery
/ B. Left subclavian vein, Ieft common carotid, superior vena cava, right atrium, right ventricle, pulmonary artery
/ C. Left subclavian vein, Ieft jugular vein, Ieft atrium, Ieft ventricle, aorta
/ D. Left subclavian vein, Ieft jugular vein, superior vena cava, right atrium, right ventricle, pulmonary artery
/ E. Left subclavian vein, superior vena cava, right atrium, right ventricle, pulmonary artery

Calcium channel blockers can be used in this setting to decrease pulmonary vascular resistance. Which of the following is the calcium
channel blocker that will have the most predominant effect on vascular smooth muscle?
/ A. Diltiazem
/ B. Hydrochlorothiazide
/ C. Nifedipine
/ D. Pseudoephedrine
/ E. Verapamil

Q 4
Which of the following physiologic stimuli will result in decreased pulmonary vascular resistance?
/ A. Decreased cardiac output
/ B. Increased cardiac output
/ C. Low O2 tension
/ D. Lung volumes near residual volume (RV)
/ E. Lung volumes near total lung capacity (TLC)

Q 5
Some of the examination findings indicate hepatic congestion. Which of the following terms is commonly used to identify the macroscopic
pattern of red, depressed hepatic nodules with pale periphery that accompanies the chronic hepatic congestion seen in this condition?
/ A. Centrilobular hemorrhage
/ B. Cirrhosis
/ C. Fatty change
/ D. Nutmeg liver
/ E. Piecemeal necrosis


Cardiomegaly Case 4 Answers
The correct answer is A. This patient has cor pulmonale, which is defined as enlargement of the right ventricle secondary to diseases of the lung, thorax, or pulmonary circulation. In this case, it is chronic, given the duration of the patient's symptoms and the presence of many clinical sequelae of the condition: edema, jugular venous distention, hepatic distention, and right ventricular heave. The electrocardiogram also supports the diagnosis of enlargement of the right ventricle showing right axis deviation due to the increase in the mass of the right heart. Evidence of right atrial enlargement is also present, i.e., the tall peaked P waves in leads II, III, and aVF (P pulmonale).
Hypertrophic cardiomyopathy (choice B) is an anomaly in which the myocardium hypertrophies. The fibers are erratic and conduction abnormalities and outflow obstruction may result. Typically, this disorder presents in the second decade of life, and will manifest as dysrhythmia and/or shortness of breath. In addition, a right axis deviation would be inconsistent with this cardiomyopathy because the left ventricle hypertrophies, as well as the right. Thus, this diagnosis is unlikely.
Left ventricular failure (choice C) often accompanies right ventricular failure, but in this case, the right-sided symptoms, such as systemic edema, jugular venous distention, and hepatic congestion, are more pronounced. Left-sided failure shows engorgement of the entire pulmonary tree in conjunction with pulmonary edema.
Myocardial infarction (choice D) is unlikely. The ECG findings are not consistent with the pattern typically seen in MI. In addition, this patient does not suffer from the symptoms of myocardial infarction, such as chest pain, pressure, jaw numbness, and diaphoresis.
Pulmonary embolus (choice E) may cause acute right heart strain and failure, but this patient has a chronic condition. Chronic emboli may produce increased resistance in the pulmonary tree and a picture similar to this.

The correct answer is A. The correct sequence for a catheter inserted into the left subclavian vein is as follows: left subclavian vein, left brachiocephalic vein, superior vena cava, right atrium, right ventricle, pulmonary artery. With this catheter in place, a variety of cardiac parameters can be measured, including pressures in the pulmonary artery. Thus, this catheter can aid in establishing the diagnosis of pulmonary hypertension

The correct answer is C. The calcium channel blockers vary in the propensity to affect vascular smooth muscle versus their effect on cardiac muscle. Thus, in this case, it is important to select an agent that has maximum ability to relax the smooth muscle in the pulmonary vessels. The effect on smooth muscle is as follows: nifedipine>diltiazem >verapamil . The effect on cardiac muscle is as follows: verapamil>diltiazem>nifedipine. Thus nifedipine is the agent of choice.
Hydrochlorothiazide (choice B) is a diuretic, and thus would have no effect on the vascular smooth muscle.
Pseudoephedrine (choice D) is an alpha agonist, and therefore would cause vasoconstriction.

The correct answer is B. A unique feature of the pulmonary circulation is that it maintains itself as a low-pressure system. Many of the mechanisms that control pulmonary vasculature differ from those of the systemic circulation. One of these features is that pulmonary vasculature resistance is decreased in response to increased cardiac output. This is accomplished through distention of open capillaries and the recruitment of collapsed capillaries. Thus, the resistance in the pulmonary tree decreases in response to increased right ventricular output. In the pathologic state of pulmonary hypertension, in which the resistance is elevated and the ventricle fails, this decreased cardiac output (choice A) may compound the problem and trigger increased resistance in spite of the primary elevation.
Low O2 tension (choice C) in the pulmonary vessels initiates vasoconstriction. In the systemic circulation, low O2 tension initiates vasodilation.
Lung volume also affects pulmonary vascular resistance. The curve of lung volume versus pulmonary vascular resistance is U-shaped. This effect is due to the fact alveolar and extra-alveolar vessels act as resistors in series (additive), and these vessels have little intrinsic support. Thus, resistance in these vessels is affected by pleural pressures. At low lung volumes (choice D), the alveolar vessels are open, but extra-alveolar vessels are compressed. At high lung volumes (choice E), the alveolar vessels are compressed by distended alveoli, but the extra-alveolar vessels become distended due to the increase in transmural pressure. Thus a U-shaped curve describes this relationship.

The correct answer is D. Chronic passive congestion of the liver leads to a macroscopic pattern known as nutmeg liver. This is due to the congestion of blood in the centrilobular region (dark) with hypoxia and fatty change in the more peripheral hepatocytes. When viewed macroscopically, this pattern resembles that seen in a cross section of a nutmeg, hence the name.
In this condition, centrilobular hemorrhage (choice A) usually only occurs in severe acute ischemia. This patient has a chronic condition, and thus most likely will have nutmeg liver instead.
Cirrhosis (choice B) of the liver may result from chronic damage caused by chronic congestion. It however produces a scarred, whitish, shrunken liver, and not the pattern seen here.
Fatty liver (choice C) would produce a large, smooth yellow liver and would not resemble the pattern seen here.
Piecemeal necrosis (choice E) is a microscopic finding of scattered hepatocellular necrosis. This diagnosis cannot be made macroscopically.

Cardiomegaly Case 3

Cardiomegaly Case 3

A 78-year-old man had been previously active, but found that his health was declining. Over a four-month period, his ability to perform even very minimal exercise, such as walking around his yard, declined precipitously. The family took him from doctor to doctor, none of whom were
initially able to figure out what was wrong with him. Because of the patient's age, most of the physicians that the family consulted were unwilling to do much other than to listen to the family's story and then run a few screening tests. In some ways, he acted as if he were in
congestive heart failure, but he initially had no evidence of fluid overload and his lungs were clear. The cardiac profile on chest X-ray was slightly enlarged. His ECG studies were interpreted as within the normal range for his age. Angiography studies showed no evidence of
significant coronary artery occlusion. Pulmonary function studies were unrevealing.

Following a Thanksgiving meal, the patient's condition worsened markedly over the next few hours, and he was taken to an emergency
department. At that point, the patient was in obvious, severe, congestive heart failure with evidence of fluid overload and pulmonary edema.
Intravenous furosemide was started, which over the next few hours markedly improved his clinical condition. Furosemide is classified as
which of the following?
/ A. Carbonic anhydrase inhibitor
/ B. Loop diuretic
/ C. Osmotic diuretic
/ D. Potassium-sparing diuretic
/ E. Thiazide diuretic

The patient is seen the following morning by a cardiologist. The cardiologist does a very careful physical examination. He notes that the heart
sounds appear distant. He then has the patient lie at an angle of 30 to 45 degrees, and does a careful examination of the right jugular pulse,
which he finds very worrisome. The pulse is both very elevated and shows dramatic x and y descents. Further, he notes that the venous
distention paradoxically increases during inspiration. This last finding is sometimes called which of the following?
/ A. Chvostek's sign
/ B. Corrigan's sign
/ C. Homans' sign
/ D. KussmauI's sign
/ E. Murphy's sign
Q 3
This patient most likely has which of the following?
/ A. Acute myocarditis
/ B. Congestive cardiomyopathy
/ C. OId left ventricle myocardial infarction
/ D. Recent left ventricle myocardial infarction
/ E. Restrictive cardiomyopathy

Q 4
An endomyocardial biopsy is performed, which demonstrates eosinophilic acellular deposits within the myocardial biopsy. When recut,
histological sections are stained with Congo red and viewed under polarized light, and the deposits appear bright green. These deposits are
most likely to be composed of which of the following?
/ A. Amyloid
/ B. Fibrin
/ C. Hemosiderin
/ D. Melanin
/ E. Uric acid

Q 5
Which of the following features of proteins is most likely responsible for the bright green appearance of the Congo red-stained materiaI?
/ A. Beta pleated sheet configuration
/ B. Calcium binding
/ C. Iron containing heme moiety
/ D. Multiple alpha helices
/ E. Presence of multiple subunits

Q 6
Which of the following would most likely be found in the Congo red-stained extracellular deposits with the bright green appearance under
polarized light?
/ A. Amyloid AA
/ B. Beta-2-microglobulin
/ C. Beta protein precursor
/ D. Immunoglobulin light chains
/ E. Transthyretin


Cardiomegaly Case 3 Answers

The correct answer is B. Large, salty, holiday meals are notorious for setting off (potentially fatal) exacerbations of what might have been previously mild congestive failure. There are a number of drugs with diuretic activity that can increase the amount of urine that is produced. Pharmacologists subclassify these drugs based on the mechanisms by which they act. Furosemide is a diuretic that is commonly used in the hospital setting in intravenous form to rapidly reduce the degree of fluid overload present in a patient in severe congestive heart failure. This diuretic acts by inhibiting the Na/K/2Cl cotransporter on the luminal membrane of the thick ascending portion of the loop of Henle. It is consequently classified as a loop diuretic, as is ethacrynic acid, which has a similar mechanism of action.
Carbonic anhydrase inhibitors (choice A), such as acetazolamide and dorzolamide, act on the proximal convoluted tubule to reduce Na+ resorption secondary to an inhibition of CO2 formation with resulting decreased intracellular bicarbonate and H+ levels.
Osmotic diuretics (choice C), such as mannitol, inhibit water reabsorption throughout the nephron.
Potassium-sparing diuretics (choice D), such as spironolactone, amiloride, and triamterene, act at the level of the collecting tubules and ducts by acting as aldosterone receptor antagonists.
Thiazide diuretics (choice E), such as hydrochlorothiazide, indapamide, and metolazone, inhibit the Na/Cl cotransporter in the distal convoluted tubule

The correct answer is D. The sign described is Kussmaul's sign. The act of inflating the lungs during inspiration lowers the pressure in the chest while increasing that in the abdomen, drawing blood from the abdomen into the chest (and increased abdominal pressure helps to directly drive blood toward the chest). If the right atrium cannot fill, then the jugular venous pressure rises paradoxically (not so much from blood flow from the head as from the abdomen, because the inferior vena cava and superior vena cava are functionally connected through the right atrium). Kussmaul's sign is seen in patients who have non-compliant right ventricles. It can also be seen in patients with severe ascites (which increases the intra-abdominal pressure). This case illustrates the importance of considering the jugular venous pulse as well as the arterial pulse, since the cardiologist was able to find a number of significant findings pertaining to the jugular venous pulse, which other physicians had missed. The jugular venous pressure can be used at the bedside to estimate the right atrial filling pressure. The jugular venous pressure is estimated by measuring the height of the visible venous pulse above the sternal angle, and then adding 5 cm (corresponding to how far below the sternum the right atrium is located). The jugular venous waveform has an A wave, which is followed by an X descent, then a V wave, and finally a Y descent. The A wave (first rise in pressure) reflects the right atrial contraction, while the X-descent reflects right atrial diastole, and then early right ventricular systole. The V wave is the second major positive wave, and reflects continued venous inflow into the right atrium in opposition to a closed mitral valve. The following Y-descent is the negative deflection that occurs when the tricuspid valve opens in early diastole.
Chvostek's sign (choice A) is seen in tetany, and is a facial muscle spasm occurring when the facial nerve is tapped anterior to the external auditory meatus.
Corrigan's sign (choice B), which suggests aortic regurgitation, is a full, hard arterial pulse, which is followed by a sudden collapse.
Homans' sign (choice C) is pain at the back of the knee or calf when the ankle is dorsiflexed, and suggests venous thrombosis of the leg.
Murphy's sign (choice E) is pain on palpation of the right subcostal area during inspiration, and is frequently seen in acute cholecystitis.

The correct answer is E. The "distant" heart sounds and jugular venous pulse findings both suggest that this patient has restrictive cardiomyopathy that is limiting the heart's ability to fill during diastole and is also impairing ventricular contraction. Other findings that may be encountered on physical examination in patients with restrictive cardiomyopathy include S3 and/or S4 heart sounds, occasional mitral or tricuspid regurgitation murmurs, and, if the patient is in secondary congestive failure, peripheral edema and pulmonary rales. Restrictive cardiomyopathy is relatively rare and the findings on physical examination are subtle, and consequently this patient's history of missed diagnosis is unfortunately not all that uncommon. Underlying causes of restrictive cardiomyopathy include endomyocardial fibrosis, Loeffler eosinophilic endomyocardial disease, hemochromatosis, amyloidosis, sarcoidosis, scleroderma, carcinoid heart disease, and glycogen storage disease. Patients typically present at an advanced stage of the disease, and may have symptoms of angina, shortness of breath, peripheral edema, and ascites with abdominal discomfort (related to pooling of blood in the liver and other abdominal organs). Once the diagnosis is suspected, echocardiography typically demonstrates normal to symmetrically thickened heart chamber walls with rapid early-diastolic filling and slow late-diastolic filling (the cardiac chambers are acting more or less like poorly distensible plastic bags). Cardiac catheterization will more or less repeat the observations seen in the analysis of the jugular venous pulse, typically showing elevated ventricular end-diastolic pressure, normal to slightly decreased ejection fraction, and prominent x and y descents.
Acute myocarditis (choice A) can cause congestive cardiomyopathy (choice B), but the heart is usually larger and the constrictive findings seen in this case would not be present.
While recent and old myocardial infarctions affecting the right ventricle may produce similar jugular venous findings to those seen in this case, left ventricular infarction (choices C and D) would not impair right ventricular filling and contraction.

The correct answer is A. Amyloid deposits are suspected when hematoxylin and eosin-stained histological sections show extracellular eosinophilic deposits. The presence of amyloidosis is confirmed when the characteristic "apple-green birefringence" on Congo red stain is demonstrated.
Fibrin deposits (choice B) are also red on hematoxylin and eosin stain, but show no fluorescence with Congo red stain.
Hemosiderin (choice C) causes yellow brown deposits; melanin (choice D) causes brown-black deposits; and uric acid (choice E) causes yellow crystalline deposits

The correct answer A. It was originally assumed by biochemists that amyloid was always composed of the same material. It came as something of a shock when antibody techniques were developed that demonstrated that the antigenicity of amyloid in different clinical settings varied markedly. The common feature these proteins shared that accounted for both the affinity for Congo red and their characteristic regular fibrillar structure on electron microscopy turned out to be that the proteins all have a beta pleated sheet tertiary (secondary according to some biochemical purists) configuration, best demonstrated by X-ray diffraction.
Selective or non-selective binding to calcium (choice B) is common in proteins.
Heme moieties containing iron (choice C) are a part of myoglobin and hemoglobin.
Alpha helices (choice D) are a common secondary structure in proteins, but do not contribute to the protein forming amyloid.
The presence of multiple subunits (choice E) is also common in proteins, but does not contribute to a protein forming amyloid.

The correct answer is D. Amyloidosis occurs in a large variety of forms. Primary amyloidosis is one of the more common forms of systemic amyloidosis, and can affect a variety of organs, including the heart, kidney, peripheral nerve, gastrointestinal tract, and respiratory tract. In primary amyloidosis, the amyloid is composed of immunoglobulin light chains, and the disease is now interpreted as a plasma cell disorder closely related to multiple myeloma. This interpretation is clinically significant, as it has led to modern treatments of primary amyloidosis (which formerly had a dismal prognosis) with the chemotherapies designed for multiple myeloma. The treatments are affective only if the disease is recognized and passed to the appropriate specialists as early as possible in the clinical course.
Amyloid AA (choice A) is seen in inflammation-associated amyloidosis and familial Mediterranean fever.
Beta-2-microglobulin (choice B) comprises the amyloid of dialysis-associated amyloidosis.
Beta protein precursor (choice C) comprises the amyloid seen in the brains of patients with Alzheimer's disease and Down syndrome.
Transthyretin (choice E) comprises the amyloid seen in familial amyloidosis and senile cardiac amyloidosis.

Cardiomegaly Case 2

Cardiomegaly Case 2

A 23-year-old man presents to the urgent care clinic complaining of severe throat pain, fever, chills, and diffuse joint pains. He first developed symptoms two weeks ago and was evaluated by another physician at the same clinic. A throat culture was done, and the patient was given a
prescription for antibiotics that he did not filI. He now returns with a worsening of his symptoms. He has since developed severe joint pain and swelling, which first affected his right wrist, then spread to both knees, and now has also affected his left ankle. He also complains of
moderate to severe chest discomfort and shortness of breath. His temperature is 38.7 C (101.6 F), blood pressure is 118/86 mm Hg, pulse is 104/min, and respirations are 20/min. There is an exudate on his oropharynx and bilateral anterior cervical lymphadenopathy. On lung examination, there are bibasilar crackles, and the cardiac examination reveals tachycardia, but a normal rhythm and no murmurs or rubs. Examination of his joints reveals synovitis in his right wrist, Ieft ankle, and both knees.

Q 1:
Which of the following is the most likely cause of this patient's cardiac findings?
/ A. Acute myocardial infarction
/ B. Aortic dissection
/ C. Mitral regurgitation
/ D. Myocarditis
/ E. Wolff-Parkinson-White (WPW) syndrome

Q 2
What underlying condition can explain the patient's upper respiratory as well as cardiac and joint signs and symptoms?
/ A. Acute rheumatic fever
/ B. Budd-Chiari syndrome
/ C. Ebstein's anomaly
/ D. Sjögren syndrome
/ E. Takayasu arteritis

Q 3
Which of the following test results would help confirm the most likely diagnosis?
/ A. EIevated antinuclear antibody
/ B. Low anti-deoxyribonuclease B titer
/ C. Low anti-hyaluronidase titer
/ D. Low anti-streptolysin O titer
/ E. Throat culture positive for group A streptococci

Q 4
A biopsy of the affected cardiac tissue would most likely show which of the following?
/ A. Angiosarcoma
/ B. Aschoff body
/ C. Atheromas
/ D. Hyperplastic arteriolosclerosis
/ E. Libman-Sacks lesions

The patient continues to deteriorate, he develops worsening heart failure, and requires transfer to the intensive care unit for use of an
inotropic agent to increase his cardiac output. Which of the following agents would most likely be used?
/ A. Benazepril
/ B. Diltiazem
/ C. Dobutamine
/ D. Metoprolol
/ E. Phenylephrine


Cardiomegaly Case 2 Answers
The correct answer is D. The patient has myocarditis, which is an inflammation of the cardiac muscle. It is most commonly the result of an infectious process. Signs and symptoms can range from an asymptomatic state to arrhythmias, heart failure, and death. The patient often has an antecedent infection, and in this case, he had an exudative pharyngitis.
Acute myocardial infarction (choice A) usually presents with severe squeezing left-sided chest pain that can radiate down the left arm. Patients are generally middle-aged, and can have risk factors for cardiac disease such as hypertension, diabetes, hypercholesterolemia, or a history of tobacco use. The electrocardiogram can vary from nonspecific T wave changes to ST segment elevation.
Aortic dissection (choice B) would present as sudden onset of severe chest pain, which often radiates to the back. Patients can have hypotension, depending on the severity of the dissection, or hypertension, which is often a predisposing factor. Patients can also have unequal pulses in their extremities, if the dissection affects one of the major arteries branching off the aortic arch.
Mitral regurgitation (choice C) is a result of mitral valve insufficiency, in which there is a regurgitant flow of blood across the mitral valve, from the left ventricle, into the left atrium, during systole. It is often due to rheumatic heart disease, but can also result from mitral valve prolapse, or papillary muscle rupture. Physical examination should reveal a holosystolic murmur, heard best at the apex.
Wolff-Parkinson-White (WPW) syndrome (choice E) is a ventricular preexcitation syndrome associated with an atrioventricular bypass track. Patients often have paroxysmal tachycardias, and an electrocardiogram will often reveal a shortened PR interval, a delta wave, and a wide QRS complex.

The correct answer is A. Acute rheumatic fever is an inflammatory disorder that affects multiple systems. There are five major criteria for rheumatic fever: carditis, migratory polyarthritis, subcutaneous nodules, Sydenham chorea, and erythema marginatum. There are also minor criteria: fever, arthralgia, elevated acute phase reactants, and a prolonged PR interval.
Budd-Chiari syndrome (choice B) is an occlusion of the major hepatic veins, which leads to congestive liver disease. Patients often have abdominal pain, jaundice, and hepatomegaly.
Ebstein's anomaly (choice C) is due to an anomalous attachment of the tricuspid leaflets, and results in downward displacement of the tricuspid valve into the right ventricle. This results in tricuspid regurgitation. Symptoms can vary from cyanosis to arrhythmias.
Sjögren syndrome (choice D) is an autoimmune disorder characterized by inflammatory changes in glands, producing dry eyes and dry mouth.
Takayasu arteritis (choice E) is a vasculitis syndrome that affects medium to large arteries, in particular, the aortic arch and its branches. It is also known as "pulseless disease" because patients have weak or absent pulses in their upper extremities. It primarily affects young Asian females.

The correct answer is E. To meet criteria for the diagnosis of rheumatic fever, patients must have either two major, or 1 major and 2 minor criteria, plus evidence of an antecedent streptococcal infection. A throat culture positive for group A streptococci would fulfill the criteria in the presence of myocarditis and migratory polyarthritis.
Elevated antinuclear antibody (choice A) is not associated with rheumatic fever. In the appropriate clinical setting, it is helpful in the diagnosis of rheumatologic disorders such as systemic lupus erythematous.
Anti-streptolysin O (choice D), anti-deoxyribonuclease B (choice B), and anti-hyaluronidase (choice C) are all streptococcal antibody tests. In the setting of rheumatic fever associated with a recent group A streptococcal infection, the titers for these antibody tests would be elevated (in the absence of infection, they may actually be undetectable). A significant titer of any of these antibody tests would meet criteria for the documentation of an antecedent streptococcal infection.

The correct answer is B. The Aschoff body is the classic lesion of rheumatic fever. It is an area of focal interstitial myocardial inflammation. It is characterized by large cells, known as Anitschkow myocytes, and Aschoff cells, which are multinucleated giant cells.
Angiosarcoma (choice A), a rare malignant tumor affecting the vascular tissue, can occur in the skin, breast, liver, or musculoskeletal system.
Atheromas (choice C) are fibrous plaques within the intima of arteries. They are a finding of atherosclerosis.
Hyperplastic arteriolosclerosis (choice D) is characterized by concentric, laminated thickening of arteriolar walls. It often occurs in the kidneys, and may lead to malignant nephrosclerosis.
Libman-Sacks lesions (choice E) are small vegetations that occur on valvular heart tissue. They can occur on either side of the valve, and are associated with endocarditis in systemic lupus erythematous

The correct answer is C. Dobutamine is a positive inotropic agent used in severe cases of heart failure that require inotropic support.
Benazepril (choice A) is an angiotensin converting enzyme inhibitor. Medications in this class can be used in heart failure to decrease afterload, but they do not have any direct affect on cardiac tissue.
Diltiazem (choice B) and metoprolol (choice D) are both negative inotropic agents. When used in the setting of acute heart failure, the patient's course can worsen, although beta blockers such as metoprolol and carvedilol (mixed alpha and beta blocker) are sometimes cautiously used in some patients with CHF.
Phenylephrine (choice E) is an alpha-receptor agonist. It causes vasoconstriction, and is used in severe cases of hypotension

Cardiomegaly case 1

Cardiomegaly case 1

A 45-year-old woman presents to her primary care physician complaining of fatigue, weight gain, and shortness of breath. She has always been an active athlete, but in the past 2 weeks, has found it impossible to jog for more than a few minutes, after which she feels tired and
winded. She feels like her appetite is normal or has even declined, but she notices that she has gained 15 pounds and her pants and shoes no longer fit welI. She has very little energy, and is sleeping poorly, with occasional difficulty breathing at night. She denies any pain, fever, or
chills. Review of her chart reveals an up-to-date health screening including a normal baseline mammogram, a normaI Pap smear in the last year, and total cholesterol of 165 mg/dL two years ago. On physical examination, she appears comfortable, has a temperature of 36.8 C
(98.2. F), blood pressure of 135/68 mm Hg, pulse of 90/min, and respiratory rate of 24/min. She appears fatigued but not in acute distress, and her skin appears normal. Expiratory wheezes are heard at the bases of both lungs. Her heart has a normal-sounding S1 and S2, with a
II/IV soft holosystolic murmur heard best at the apex of the heart. Her abdomen is modestly distended, and her ankles are edematous. A chest x-ray film reveals cardiomegaly as well as increased vascular markings in the lung beds and bilateral small pleural effusions.

Q 1
Which of the following is the most likely diagnosis?
/ A. Acute leukemia
/ B. Cardiomyopathy
/ C. Fibromyalgia
/ D. Hypothyroidism
/ E. Major depressive disorder

Q 2
Which of the following is the most likely cause of the patient's murmur?
/ A. Aortic insufficiency
/ B. Aortic stenosis
/ C. High-output flow murmur
/ D. Mitral regurgitation
/ E. Mitral stenosis
/ F. Pulmonic insufficiency
/ G. Pulmonic stenosis
/ H. Tricuspid regurgitation
/ I. Tricuspid stenosis

Q 3
BIood in the pulmonary veins is at the same pressure (during all phases of the cardiac cycle) as blood in which of the following?
/ A. Aorta
/ B. Left atrium
/ C. Left ventricle
/ D. Right atrium
/ E. Right ventricle

Q 4
To improve her shortness of breath, the patient is given furosemide. What is the molecular mechanism and site of action of this drug?
/ A. ADH antagonism of in the collecting ducts
/ B. AIdosterone antagonism in the distal tubule
/ C. BIockade of sodium reabsorption in the proximal tubule
/ D. BIockade of sodium transport in the distal tubule
/ E. Inhibition of carbonic anhydrase in the proximal tubule
/ F. Inhibition of sodium-potassium-chloride cotransport in the loop of Henle

Q 5
What important physiologic effect will starting this patient on an angiotensin-converting-enzyme inhibitor achieve?
/ A. Decrease in arteriolar resistance, resulting in less resistance to forward cardiac output
/ B. Decrease in cardiac filling pressures, resulting in less pulmonary congestion
/ C. Increase in arteriolar resistance, resulting in improved blood pressure
/ D. Increase in left-ventricular end-diastolic volume, improving stroke volume via Starling forces
/ E. Increase in myocardial contractility, resulting in improved stroke volume
/ F. Stabilization of myocardial membranes, resulting in reduced risk of arrhythmia


Cardiomegaly Case 1 Answers

The correct answer is B. This woman has many of the classic symptoms of heart failure, with symptoms of both poor forward cardiac output (fatigue, poor appetite) and of vascular congestion in both the right and left atria (edema, abdominal distension that may be ascites, cardiomegaly, pulmonary vascular congestion and effusions seen on chest x-ray, dyspnea with exertion, and paroxysmal nocturnal dyspnea.)
Acute leukemia (choice A) is a potential cause of fatigue, poor energy, and poor nutritional status (which can cause edema and pleural effusion). Usually some abnormality will be apparent, most commonly pancytopenia, due to replacement of bone marrow with leukemic cells; the leukocyte count may be elevated due to the presence of leukemic cells in the peripheral blood. They often present with bleeding or infectious complications of pancytopenia. Anemia could potentially cause a murmur due to elevated cardiac output, but an acute leukemia would not typically cause cardiomegaly or pulmonary edema.
Fibromyalgia (choice C) is a potential cause of fatigue, poor energy, and poor sleep, especially in women ages 25-45: its principal sign, however, is diffuse musculoskeletal pain and stiffness, with characteristic tender trigger points. It is not consistent with this patient's chest x-ray abnormalities or cardiac and lung findings.
Based on examination, this patient could certainly have hypothyroidism (choice D). Symptoms are usually insidious in onset and include fatigue, poor appetite with weight gain, poor sleep and possibly, obstructive sleep apnea. Patients often complain of constipation, cold intolerance, stiffness and muscle cramping, as well as decreased intellectual activity. Severe hypothyroidism can result in cardiomegaly, pericardial effusion, and symptoms of cardiac failure. The skin often appears dry, rough, and doughy in texture. The normal TSH, however, makes hypothyroidism in this patient very unlikely: The TSH is nearly always elevated, as most hypothyroidism is primary, which means the pituitary is secreting maximal TSH in an attempt to stimulate a hypofunctional thyroid gland. Rarely, TSH may be normal or depressed (even undetectable) in pituitary or hypothalamic failure. To rule this out, one might test first for T4 and T3 levels. Normal levels of these, in conjunction with the normal TSH, would rule out hypothyroidism as a cause of this clinical presentation.
Major depression (choice E) should always be in the differential for a patient who presents with disturbances in sleep, appetite, and energy, and can also result in weight loss or gain. These "vegetative signs" of depression may be the presenting abnormality in a depressed patient who does not note a mood disturbance themselves. One should also ask about depressed mood, anhedonia (loss of interest in or inability to take pleasure in activities the person normally enjoys), an inability to concentrate and carry on usual intellectual activities, feelings of worthlessness or guilt, and suicidal ideation. Depression cannot, however, on its own, produce the physical findings this patient has, which taken together, are worrisome for some physiologic abnormality.

The correct answer is D. Mitral regurgitation is characterized by a holosystolic murmur heard best at the apex, often with a blowing sound, which may radiate to the axilla.
The murmur of aortic insufficiency (choice A) is a decrescendo diastolic murmur. Remember that the aortic valve is open during systole; a systolic murmur, then, cannot represent regurgitant aortic flow due to an improperly closed valve.
Aortic stenosis (choice B) does produce a systolic murmur caused by turbulent flow across a narrowed aortic valve during systole. This murmur is usually a crescendo-decrescendo murmur, often with a harsh quality, and is characteristically heard best at the base of the heart; it may radiate to the carotids as well.
High-output states (choice C) can cause a similar soft systolic murmur to that described here. However, this patient's history is most consistent with cardiac failure, which is a low-output state.
Mitral stenosis (choice E) causes a murmur due to turbulent low-velocity flow during diastolic filling of the left ventricle through a narrowed mitral orifice. This results in a soft diastolic murmur heard best at the apex. Remember that the mitral valve is closed during systole, therefore, an abnormal mitral sound in systole must be the sound of abnormal regurgitant flow through a closed valve.
The right-sided murmurs are less common, similar in quality, and usually less loud than the left-sided murmurs (given that pressures on the right are usually lower):
Pulmonic insufficiency (choice F), when audible, therefore causes a soft diastolic murmur at the right upper sternal border.
Pulmonic stenosis (choice G) causes a crescendo-decrescendo systolic murmur also heard at the base of the heart.
Tricuspid regurgitation (choice H) causes a holosystolic murmur at the left lower or right lower sternal border.
Tricuspid stenosis (choice I) when audible, is a diastolic murmur heard best at the same location

The correct answer is B. The pressures in two chambers, which are not separated by a closed valve, will be equal. The pulmonary vein empties into the left atrium, and no valve separates the two chambers, therefore the pressures are equal in all phases of the cardiac cycle. This patient's pulmonary vascular congestion is likely due to elevated pulmonary venous pressure, which is, in turn, likely due to elevated left atrial pressures.
Pressures in the aorta (choice A) will be higher than pressures in the pulmonary veins during the cardiac cycle.
The left ventricle (choice C) is separated from the left atrium and the pulmonary veins by the mitral valve. The pulmonary veins and the left atrium are at the same pressure as the left ventricle during diastole, when the mitral valve is open. With complete mitral insufficiency, the pulmonary veins are completely exposed to left ventricular pressures during systole, resulting in severe pulmonary edema.
The right atrium (choice D) is not in communication with the pulmonary veins, being separated from them by, in sequence, the tricuspid valve, the right ventricle, the pulmonic valve, the pulmonary arterial system, and the pulmonary capillary bed.
The right ventricle (choice E), during systole, is at the same pressure as the pulmonary artery, not the pulmonary veins. During diastole, the pulmonary arterial pressure exceeds right ventricular pressure, and the valve is closed.

The correct answer is F. The Na-K-2Cl cotransporter in the loop of Henle operates via an ATP-dependent sodium-potassium exchange pump in the cell that creates a gradient for sodium diffusion from the urine space into the cell. This maintains the sodium concentration gradient of the renal medulla. Furosemide is the most commonly used loop diuretic; it acts by blocking the action of the cotransporter in the thick ascending limb of the loop of Henle.
ADH antagonism (choice A) is not an important diuretic drug mechanism, however, certain drugs, most notably lithium, inhibit ADH's action, resulting in nephrogenic diabetes insipidus.
Aldosterone promotes the reabsorption of sodium in the late distal tubule and collecting system and promotes the excretion of potassium. Aldosterone receptor antagonism (choice B) is the mechanism of action of potassium-sparing diuretics such as spironolactone.
Sodium reabsorption in the proximal tubule (choice C) is a largely passive process, which is coupled to the transport of organic solutes and anions and also to chloride transport, via both transcellular and paracellular mechanisms.
The thiazide diuretics work primarily by blocking sodium transport in the early portion of the distal tubule (choice D).
Acetazolamide inhibits carbonic anhydrase (choice E), preventing the luminal transformation of bicarbonate into CO2, which diffuses back into the cell. Inhibition of this enzyme increases both bicarbonate and sodium concentrations in the urine, resulting in high urine pH and metabolic acidosis.

The correct answer is A. In cardiac failure, the juxtaglomerular apparatus releases renin in response to low blood pressure or low flow states. Renin cleaves angiotensinogen into angiotensin I, which is then cleaved by angiotensin-converting enzyme (ACE) into angiotensin II. Angiotensin II is a potent vasoconstrictor and increases blood pressure. This, however, increases the resistance against which the heart must pump, thereby reducing cardiac output. By reducing angiotensin II activity, systemic vascular resistance (normally high in cardiac failure, in an attempt to maintain blood pressure in the presence of low flow) is reduced, permitting the heart to eject more volume against a lower aortic pressure. This is often described as "afterload reduction" and is the mainstay of therapy in congestive heart failure. Paradoxically, blood pressure may not change: the reduced resistance, by permitting increased flow, may result in no net change in pressure. This is most easily understood as a physiologic manifestation of Ohm's law: V = IR. In electricity, this law means that voltage is equal to current times resistance. Blood pressure is analogous to voltage, cardiac output to current flow, and the resistance in this case is the resistance of the systemic vasculature.
Reduction of cardiac filling pressures (choice B) or "preload," is also an important aspect of the treatment of heart failure. In heart failure, the heart operates at high filling pressures and high left ventricular end-diastolic volume (LVEDV) because both aldosterone and ADH promote the retention of fluid in response to low forward flow and decreased effective circulating volume. The result is vascular congestion in the pulmonary veins due to the high LV diastolic pressure, resulting in symptomatic pulmonary edema. By reducing this preload, congestive symptoms can be relieved, and LVEDV can be reduced without significant loss of stroke volume. ACE inhibitors, however, do not reduce preload: drugs that do this are nitrates (which act as venodilators) and diuretics.
Increasing arteriolar resistance (choice C) in heart failure increases the "afterload" against which the heart must eject and does not improve cardiac output.
Increasing LVEDV (choice D) is usually helpful in hypovolemia or other states in which inadequate volume is available to the heart, thereby limiting cardiac output. This happens in the portion of the Starling curve at low LVEDV, where an increase in LVEDV results in a large increase in stroke volume. Patients in symptomatic heart failure like this patient operate at very high LVEDV and benefit from its reduction.
Increasing myocardial contractility (choice E) is beneficial in heart failure, and is the mechanism of action of inotropic drugs. This is not a mechanism of ACE inhibitors.
Prevention of arrhythmia (choice F) is also important in heart failure, as the dilated heart is vulnerable to both atrial and ventricular arrhythmias. This is not a direct action of ACE inhibitors, however.

Sunday, January 10, 2010

Shortness Of Breath Case 5

Shortness Of Breath Case 5

A 20-year-old woman is brought to the emergency department after a severe traffic collision. Initial assessment reveals a tachypneic, tachycardic, hypotensive woman in acute distress. On examination, she has multiple contusions on the left Iateral chest wall and jugular venous distention (JVD). Her chest is hyperresonant to percussion and she has diminished breath sounds on the left. Her trachea deviates to the right. A chest x-ray film reveals diminished vascular markings on the Ieft. An ECG shows sinus tachycardia.

Which of the following is the most likely diagnosis?

/ A. Cardiac contusion
/ B. Hypovolemic shock
/ C. Pericardial tamponade
/ D. Pulmonary contusion
/ E. Tension pneumothorax

Which of the following is the most likely mechanism of this patient’s shock?

/ A. Fiuid in the pericardial space prevents diastolic filling
/ B. Hypoxia from rapid loss of pulmonary capacity impedes cardiac function
/ C. Malpositioning of the great vessels has impeded venous return
/ D. Massive bleeding into the pleural space has led to hypovolemia
/ E. Myocardial dyskinesia has led to cardiac insufficiency

Which of the following is the most appropriate immediate management?

/ A. FIuid bolus
/ B. Needle thoracostomy
/ C. Open thoracotomy
/ D. Pacemaker placement
/ E. Pericardiocentesis

When instrumenting the chest, instruments are inserted into the chest along the superior surface of the rib to avoid which of the following structures?

/ A. External oblique muscle
/ B. Intercostal artery
/ C. Parietal pleura
/ D. Phrenic nerve
/ E. Visceral pleura


Shortness Of Breat Case 5 Answers

The correct answer is E. This patient has the classic findings for tension pneumothorax. She has a history of severe trauma, and the findings of dyspnea, tachypnea, tachycardia, tracheal deviation, unilaterally decreased breath sounds, and hyperresonance to percussion. This is a life-threatening condition that must be remedied immediately.
Cardiac contusion (choice A) would not present with these findings. Patients will be hemodynamically unstable, often showing various arrhythmias on ECG. They will not have tracheal deviation, JVD, or hyperresonance to percussion.
Hypovolemic shock (choice B) could not account for the patient's jugular venous distention, hyperresonance to percussion, diminished breath sounds, tracheal, or chest x-ray findings.
Pericardial tamponade (choice C) is a life-threatening condition often seen in the trauma setting. Beck's triad characterizes pericardial tamponade: decreased heart sounds, jugular venous distention, and hypotension. Patients may also be tachycardic with pulsus paradoxus.
Pulmonary contusion (choice D) may produce respiratory distress immediately after trauma occurs but usually complicates the chronic course. It would not produce tracheal deviation, or hyperresonance to percussion. On x-ray films it would appear as an ill-defined opacity.

The correct answer is C. As discussed above, this patient is suffering from tension pneumothorax, and the mechanism of shock in this condition is mechanical. As air becomes trapped in the pathologic side of the chest, the ipsilateral chest cavity expands. The enlarging cavity begins to encroach upon the mediastinal and contralateral chest contents, and as the contents herniate contralaterally, the great vessels become kinked and compressed. This inhibits venous return and thus diastolic filling. This results in shock. Immediate decompression of the chest will restore venous return.
As discussed above, this patient does not have pericardial tamponade (choice A). In pericardial tamponade, fluid in the pericardial sac surrounding the heart prevents diastolic filling, resulting in shock. Immediate decompression of the pericardial space is indicated.
While hypoxia (choice B) may result from pneumothorax, this is not the primary reason for the patient's shock.
Massive bleeding into the pleural space (hemothorax; choice D) may cause shock in a fashion similar to pneumothorax. It is unlikely that this patient has a hemothorax, however, as evidenced by the hyperresonance to percussion.
Choice E is incorrect. Severely contused myocardium would likely show ECG abnormalities. A normal ECG makes this diagnosis less likely, and thus not a likely reason for this patient's shock.

The correct answer is B. Since the tension within the chest cavity creates the danger, relieving it is the mainstay of treatment. Continued tension will continue to push the chest contents to the side contralateral to injury. This will "kink" the venous return to the heart leading to diminished end-diastolic volume with imminent cardiac collapse. In addition, the uninjured lung will have limited inspiratory capacity. Thus to accomplish immediate decompression, a needle is inserted in the second intercostal space at the mid-clavicular line.
This is followed by placement of a chest tube to manage the pneumothorax more chronically. This patient may have hypovolemia, as bleeding may be present, but her hemodynamic instability may be entirely due to the tension pneumothorax. Thus, fluid (choice A) may be given later, but treating the pneumothorax is a higher priority.
Open thoracotomy (choice C) would treat the pneumothorax, but would take longer than needle decompression, and may be more than is needed.
This case has given no justification for pacing the heart (choice D).
Pericardiocentesis (choice E) is used to treat pericardial tamponade, not pneumothorax.

The correct answer is B. The intercostal vein, artery, and nerve traverse the inferior surface of the ribs in the intercostal groove. When placing instruments into the chest, these structures must be avoided. Damaging these structures can result in bleeding into the chest and may cause significant hemothorax. Thus, instruments are inserted along the superior surface of the rib.
The external oblique muscle (choice A) runs between the ribs from superior to inferior and laterally to medially. (Like the fingers of a hand placed in pants pockets.) This structure in invariably pierced when instrumenting the chest.
The parietal pleura (choice C) is the layer of pleura that adheres to the chest wall. It is also pierced when instrumenting the chest.
The phrenic nerve (choice D) innervates the diaphragm from spinal segments C3-5. It travels in the mediastinum and would not be at risk here.
The visceral pleura (choice E) is the thin layer of pleura that envelops the lung. It would be at risk for damage if the instruments were inserted into the chest too far. Placing the instrument in the proper orientation to the rib is of no consequence

Shortness Of Breath Case 4

Shortness Of Breath Case 4

A 55-year-old man presents to the emergency department complaining of the acute onset of severe shortness of breath.
His only associated symptom is a dry cough productive of scant frothy sputum. He has a 70 pack-year smoking history and has had two similar episodes in the past two years. On examination, he is afebrile, tachypneic, and distressed, but without cyanosis. He is thin, and his accessory muscles contract with each breath. He exhales through pursed lips. His chest examination reveals diminished breath sounds with hyperresonance to percussion.

Which of the following is the most likely diagnosis?

/ A. Chronic bronchitis
/ B. Cystic fibrosis
/ C. Emphysema
/ D. Myocardial infarction
/ E. Pneumonia

In this disorder, the mechanism for decreased FEV1 (forced expiratory volume in 1 second) is which of the following?

/ A. Airway collapse due to loss of elastic recoil
/ B. Airway constriction due to bronchospasm
/ C. Biockage of airways by increased mucus production
/ D. Decreased lung compliance due to pulmonary fibrosis
/ E. Lung collapse due to air in the pleural space

Which of the following drugs might prove helpful in treating this patient?

/ A. Acetazolamide
/ B. Aibuterol
/ C. Metoprolol
/ D. Metronidazole
/ E. Propranolol

Which of the following sets of changes depict the mean arterial pressure (MAP), Ieft ventricular peak systolic pressure (LVPSP), pulmonary wedge pressure (PWP), and left atrial pressure (LAP) in this patient, compared to a healthy individuaI?

An inherited form of this disease can result from which of the following?
/ A. A deficiency of alveolar dipalmitoyl phosphatidylcholine
/ B. A deficiency of serum alpha-1-antitrypsin
/ C. A deficiency of serum angiotensin converting enzyme.
/ D. An elevated alveolar dipalmitoyl phosphatidylcholine
/ E. An elevated serum alpha-1-antitrypsin
/ F. An elevated serum angiotensin converting enzyme

Which of the following nerves provides innervation to the diaphragm?

/ A. Accessory nerve
/ B. Intercostal nerve
/ C. Phrenic nerve
/ D. Splanchnic nerve
/ E. Vagus nerve
Shortness Of Breath Case 4 Answers

The correct answer is C. Patients with COPD may be clinically classified as "pink puffers" or "blue bloaters" based on several characteristics. This patient is exhibiting the classic presentation for an emphysematous "pink puffer"; the patient has dyspnea but is not cyanotic. "Pink puffers" maintain their oxygenation until they decompensate precipitously. In contrast, the "blue bloater" counterparts with chronic bronchitis (choice A) have a chronic productive cough with cyanosis.
Cystic fibrosis (choice B) is an inherited disease involving a defective chloride channel, and tends to affect patients at a younger age. The defective chloride channel leads to viscous mucus that is difficult to clear. As a result, patients develop chronic lung infections and fibrotic lung disease.
Myocardial infarction (choice D) classically presents as crushing substernal chest pain, shortness of breath, and diaphoresis. Pain may radiate to the jaw and be accompanied by nausea. If congestive heart failure is present, patients may have dry cough, scant sputum, and rales on exam.
Pulmonary infections may precipitate COPD exacerbations, but this patient's presentation is not consistent with pneumonia (choice E) . Pneumonia presents as dyspnea, fever, and productive cough.

The correct answer is A. Patients with emphysema, a form of chronic obstructive lung disease, suffer from a loss of elastic recoil in the lung. As a patient exhales, the airways collapse, trapping air distal to the bronchiole. As a result of airway collapse, patients with emphysema have increased resistance to outflow, and a decreased FEV1.
Asthma, another form of COPD, results from the obstruction of small airways due to bronchoconstriction (choice B).
Blockage of airways due to mucus production (choice C) characterizes chronic bronchitis. While this obstruction produces COPD, it is not consistent with emphysema.
Pulmonary fibrosis (choice D) would increase bronchiolar elasticity and therefore would increase FEV1.
Lung collapse due to air in the pleural space (choice E) describes pneumothorax. This does not explain the decrease in FEV1 in emphysema.

The correct answer is B. Albuterol is a beta-adrenergic agonist and, as such, promotes bronchial smooth muscle relaxation, and thus bronchodilation. Bronchodilation may relieve symptoms in COPD patients with acute exacerbation. Methylxanthines and/or anti-cholinergics may provide an adjunct to beta agonists.
Acetazolamide (choice A) is a carbonic anhydrase inhibitor used as a diuretic. There is nothing in this patient to suggest that he is volume overloaded, and diuretics would thus be inappropriate.
Propanolol and metoprolol (choices C and E) are beta blockers and may actually exacerbate this patient's symptoms through bronchoconstriction.
Metronidazole (choice D) is an antimicrobial agent. While antibiotics are often used to treat infections that may exacerbate COPD, metronidazole is not an appropriate agent to treat the pathogens that typically infect people with COPD: Haemophilus influenzae, Strep. pneumoniae, and Moraxella catarrhalis.

The correct answer is A. The elastic recoil of the lungs is decreased in emphysema. This causes the chest wall to expand sufficiently to create a new balance between the elastic recoil of the lungs and chest wall, which increases the functional residual capacity. Because the lungs are expanded to higher than normal levels, both the total lung capacity and residual volume are chronically increased. The vital capacity of the lungs (which is the difference in volume between the total lung capacity and residual volume) is decreased in emphysema because the patient cannot expel normal amounts of air from the lungs.

The correct answer is B. Alpha 1-antitrypsin deficiency is associated with familial emphysema. Patients may have decreased (heterozygote) or absent (homozygote) amounts of the protease inhibitor alpha 1-antitrypsin. The precise mechanism in producing emphysema is unclear, but patients with this deficiency typically have severe disease, often with an early age of onset. Choice E therefore cannot be correct.
Dipalmitoyl phosphatidylcholine (choices A and D) is a component of alveolar surfactant, which reduces alveolar surface tension. Not only does this surfactant reduce the surface tension, it changes surface tension with changing diameter. This prevents atelectasis by allowing interconnected alveoli with different diameters to remain open at the same alveolar pressures. (Without surfactant, the Law of LaPlace dictates that it takes greater alveolar pressures to open a smaller alveolus.)
Elevated or decreased angiotensin converting enzyme (ACE; choices C and F) would not produce emphysema. ACE converts angiotensin I to angiotensin II, which has many effects on vascular and renal physiology, but is not associated with emphysema.

The correct answer is C. The phrenic nerve originates from cervical roots 3, 4, and 5 to provide innervation to the diaphragm. This is significant because spinal cord injury above this level renders the patient unable to breathe.
The accessory nerve (choice A), provides motor innervation to the trapezius and the sternocleidomastoid muscles.
The intercostal nerves (choice B) innervate the intercostal muscles responsible for chest wall expansion and retraction.
The splanchnic nerve (choice D) provides motor and autonomic fibers to the gut.
The vagus nerve (choice E) provides motor innervation to the vocal cords, heart, bronchus and GI tract. In addition it provides sensory innervation to the bronchus, heart, GI tract and larynx.

Shortness Of Breath Case 3

Shortness Of Breath Case 3

A 3-year-old boy is brought to the emergency department with shortness of breath. His parents report that he has had several episodes in which he breathes heavily and turns blue. During these episodes, he is often found squatting, which appears to relieve his symptoms. His parents brought him in today, because the boy lost consciousness. On examination, he is a poorly developed, thin boy who is in acute distress. His skin appears blue, and he has labored breathing with chest retractions A systolic ejection murmur is auscultated at the left third intercostal space. A chest x-ray film shows a smalI, "boot shaped" cardiac silhouette. The boy is admitted to the hospitaI.

Which of the following is the most likely diagnosis?

/ A. Coarctation of the aorta
/ B. Ebstein's anomaly
/ C. Patent ductus arteriosus
/ D. Tetralogy of Fallot
/ E. Transposition of the great vessels

A complete blood count is performed, and the hemoglobin is markedly increased. Which of the following substances triggers this erythrocytosis?

/ A. Aidosterone
/ B. Angiotensin ll
/ C. Erythropoietin
/ D. Interleukin 1
/ E. Renin

While this patient is in the hospital he begins to have fever and headache. On examination, he has numbness of the right side of his face, but no nuchal rigidity. A head CT shows a focal lesion with a hypodense center surrounded by a ring of enhancement. Which of the following is the most likely diagnosis?

/ A. Brain abscess
/ B. Guillain-Barr syndrome
/ C. Meningitis
/ D. Stroke
/ E. Tuberculosis

A brain biopsy from this patient grows gram-positive cocci in chains. Which of the following is the most appropriate treatment?

/ A. Cefazolin
/ B. Ceftriaxone
/ C. Fiuconazole
/ D. Metronidazole
/ E. Penicillin

Which of the following sets of changes depict the oxygen partial pressures in the aorta, Ieft ventricle, right atrium, and vena cava of this patient during resting conditions, compared to a healthy individuaI?


Shotness Of Breath Case 3 Answers

The correct answer is D. Tetralogy of Fallot is a congenital heart anomaly that presents as respiratory distress, cyanosis, clubbing, syncope and sudden death. Historical findings often include reports of "Tet spells," in which the patient is found squatting to relieve respiratory symptoms. Examination findings include a systolic ejection murmur, clubbing, and cyanosis. A characteristic small "boot-shaped" cardiac silhouette is seen on chest x-ray. The anatomic defects of this tetralogy are pulmonary stenosis, overriding aorta, right ventricular hypertrophy, and ventricular septal defect. This anatomic tetralogy results in a right-to-left shunt, and thus a marked decrease in pulmonary blood flow. The severity of symptoms depends on the degree of decrease in pulmonary blood flow. The squatting increases systemic vascular resistance, and decreases the right-left shunt.
Coarctation of the aorta (choice A) is a narrowing of the thoracic aorta. Patients may have headache, epistaxis, and lower extremity claudication. On examination, patients have diminished lower extremity pulses, and a systolic or continuous murmur. This defect may be associated with CHF, aortic dissection, intracranial aneurysmal rupture, and bacterial endocarditis.
Ebstein's anomaly (choice B) is an abnormal tricuspid valve placement that creates an abnormally large right atrium and small right ventricle. The disorder may present with cyanosis, but the clinical presentation may vary. You should suspect Ebstein's anomaly when there is a history of maternal lithium ingestion.
Patient ductus arteriosus (choice C) involves a right to left shunt that may present as acyanotic respiratory distress. It will have a continuous "machinery" murmur.
Transposition of the great vessels (choice E) typically presents as cyanosis and CHF in the neonatal period. An "egg shaped" cardiac contour is seen on chest x-ray films.

The correct answer is C. Erythropoietin is released from the kidney in response to renal hypoxia. This circulates to the red marrow and stimulates erythropoiesis, a process by which erythropoietic stem cells differentiate into red blood cells.
Aldosterone (choice A) is a hormone released from the adrenal cortex in response to angiotensin II. It triggers sodium retention in the renal collecting ducts.
Angiotensin II (choice B) is a hormone created by a series of enzymatic steps. These steps are carried out when the kidney releases renin in response to decreased flow in the area of the renal tubule known as the macula densa.
Interleukin 1 (choice D) is an inflammatory mediator. It has no effect on erythropoiesis.
Renin (choice E) is an enzyme released by the kidney in response to decreased flow in the renal tubule. It initiates a cascade of enzymatic steps to create angiotensin II, which has several vascular, renal, and endocrine effects.

The correct answer is A. Patients with cyanotic heart disease (most commonly tetralogy of Fallot ) may develop a brain abscess. In chronically hypoxic patients, polycythemia with increased blood viscosity leads to poor cerebral capillary flow and reduced tissue oxygenation. This poorly perfused segment acts as a nidus for infection, and as a result, patients with tetralogy of Fallot suffer from brain abscesses. This is a typical presentation for a brain abscess, which may include fever, headache, seizures, nuchal rigidity, papilledema, and focal neurologic defects. The CT findings are also classic for brain abscess.
Guillain-Barre syndrome (choice B) is an acute inflammatory demyelinating polyneuropathy. It typically presents as ascending weakness usually beginning in the legs. It does not present as focal CNS findings.
Meningitis (choice C) would present as headache and fever, but focal findings on neurologic examination and on CT would be unusual. Nuchal rigidity is often present.
Stroke (choice D) would be unusual in this age group. In addition, the focal lesion seen on CT does not describe the findings of stroke. CT findings for stroke vary with the etiology of the stroke, but are typically less well circumscribed and do not display ring enhancement.
Tuberculosis (choice E) could produce a meningitis, which afflicts the very old and very young. It has a long, protracted course as symptoms of fever, headache and nuchal rigidity tend to develop over a two-week course. A focal lesion would not be seen on CT scan.

The correct answer is B. The finding of gram-positive cocci in chains indicates the abscess contains streptococci. An antibiotic must not only be effective against these organisms, it must also penetrate the blood-brain barrier. Ceftriaxone is a third generation cephalosporin that penetrates the BBB. While the effectiveness against gram-positive organisms decreases as one moves from first to second to third generation cephalosporins, unless the medication arrives at the proper site, it cannot be effective.
Cefazolin (choice A) is a first generation cephalosporin. It would kill streptococci, but it would not access the CNS.
Fluconazole (choice C) is an antifungal agent. The culture indicates streptococci. Fungal brain abscess would be unusual in an immunocompetent patient.
Metronidazole (choice D) is an antiparasitic that also has activity against gram-negative organisms. It would be appropriate to use in conjunction with ceftriaxone in an empiric setting. Once the definitive cause is known, discontinuing extraneous antibiotics is appropriate.
Penicillin (choice E) would kill streptococci, but it could not access the CNS in the presence of an intact blood-brain barrier.

The correct answer is C. In Tetralogy of Fallot, the aorta originates from the right ventricle or overrides the septum, and therefore receives blood from both ventricles. This decreases the oxygen tension of aortic blood. Blood flowing through the lungs is still oxygenated normally, causing the oxygen tension of blood in the left ventricle to be normal. Because the oxygen content of the arterial blood is lower than normal, the oxygen tension of the venous blood (and therefore blood in the right atrium) is lower than normal

Shortness Of Breath Case 2

Shortness Of Breath Case 2

A 7-year-old child is taken to the emergency department because he is feeling short of breath. The episode began about an hour previously while the child was playing sports, when he abruptly developed paroxysms of wheezing and coughing.
When the physician enters the room, he notes that the child is sitting leaning forward and is using his accessory respiratory muscles. Physical examination demonstrates tachypnea and tachycardia. On auscultation, a prolonged expiratory phase with relatively high-pitched wheezes through much of the respiratory cycle are heard. No fine crackles are heard

Which of the following is the most likely diagnosis?
/ A. Asthma
/ B. Bronchiectasis
/ C. Pneumonia
/ D. Pulmonary edema
/ E. Pulmonary embolus

If pulmonary studies were performed, which of the following would be most likely to be markedly decreased?

/ A. Forced expiratory volume in the first second
/ B. Functional residual capacity
/ C. Pulmonary blood flow
/ D. Residual volume
/ E. Total lung capacity

The diagram below shows spirographic tracings of forced expirations from a healthy child (trace X) and from the 7-year-old patient (trace Z).

Which of the following is the FEV1/FVC ratio of the normal child and the patient?

Normal Patient
/ A. 1.0 0.2
/ B. 0.8 0.5
/ C. 0.7 0.3
/ D. 0.5 0.8
/ E. 0.2 1.0

Which of the following medications will have the fastest onset if the 7-year-old child has an acute attack of his condition?
/ A. Aibuterol inhalation
/ B. Beclomethasone inhalation
/ C. Ephedrine oral
/ D. Salmeterol inhalation
/ E. Theophylline oral tablets

Approximately an hour after the acute management began, the child began to bring up tenacious, rubbery, white sputum.
The sputum is examined in the laboratory and Charcot-Leyden crystals are found. These are composed of which of the following?

/ A. Bilirubin
/ B. Calcium phosphate
/ C. Cystine
/ D. Protein
/ E. Uric acid

When the child is discharged, he is placed on both albuterol and flunisolide inhalation preparations. The physician should instruct the child to use flunisolide and albuterol in which of the following ways?

/ A. These agents should not be used together
/ B. Use albuterol several minutes before the flunisolide
/ C. Use albuterol several minutes after the flunisolide
/ D. Use albuterol several hours after the flunisolide
/ E. Wash out his mouth before each use

Which of the following drugs is a leukotriene modifier indicated for the prophylaxis and treatment of asthma in this child?

/ A. Bitolterol
/ B. Cromolyn sodium
/ C. Ipratropium
/ D. Montelukast
/ E. Theophylline

Later in life, the patient develops hypertension. Assuming that his respiratory condition is still present, which of the following agents would be the most appropriate pharmacotherapy?

/ A. Atenolol
/ B. Nadolol
/ C. Propranolol
/ D. Sotalol
/ E. Timolol


Sortness Of Breath Case 2 Answers

The correct answer is A. This patient most likely has asthma based on the initial presentation. Asthma is characterized by reversible airway obstruction, airway inflammation, and bronchospasm of the airways in response to a variety of stimuli. These stimuli may include exposure to known allergens, viral infections, exercise, cold air, crying, screaming, and hard laughing. It is conventional to subdivide asthma into extrinsic (allergy-related) and intrinsic (not related to allergy) subtypes, although this subclassification has been challenged because many patients have overlapping features. The physical features illustrated in this case are typical of a severe asthma attack.
Bronchiectasis (choice B) would not produce episodes of reversible airway obstruction, and would present with fever, cough, and moist crackles.
Pneumonia (choice C) and pulmonary edema (choice D) would develop more slowly, and would be likely to show fine crackles on auscultation.
Pulmonary embolus (choice E) would be very unusual in a young child.

The correct answer is A. The forced expiratory volume in the first second (FEV1) is a commonly used pulmonary function test that evaluates the degree of obstruction present that limits expiration. The degree to which it is reduced is a measure of the severity of the asthmatic attack. In this case, in which the child is in obvious severe respiratory distress, the FEV1 should be markedly decreased.
In many asthmatic patients, functional residual capacity (choice B), residual volume (choice D), and total lung capacity (choice E) are increased.
Pulmonary blood volume (choice C) is not usually measured in asthma, but would be expected to be normal or increased (if PO2 drops).

The correct answer is B. A forced expiration is the simplest test of lung function. The individual breathes in as much air as the lungs can hold and then expels the air as rapidly and as far as possible. The forced vital capacity (FVC) is the vital capacity measured with a forced expiration (FVC = 3 L for patient Z). The forced expiratory volume in one second (FEV1) is the amount of air that can be expelled from the lungs during the first second of a forced expiration (FVC @ 1.5 L for patient Z). FEV1/FVC therefore is a function of airway resistance. Airway resistance is often increased during an asthma attack, which causes FEV1/FVC to decrease. FEV1/FVC is 0.5 in patient Z (1.5/3.0) and 0.8 in the healthy child represented by trace X (4/5).

The correct answer is A. This question is assessing your ability to understand the onset of action for each of the answer choices. We have provided a summary table of the sympathomimetic bronchodilators and selected pharmacokinetic properties.

Based on the chart above you can see that albuterol is indicated for use in the treatment of acute signs and symptoms of asthma since its onset is in less than 5 minutes.
Beclomethasone (choice B) is a glucocorticoid agent, and not a sympathomimetic. It would not have the rapid onset of action required in this case.
Although dosage forms are generally not found on USMLE Step 1, you should immediately recognize that any medication administered orally must be absorbed from the intestinal tract and then reach the site of action. Therefore, you should be able to conclude that oral ephedrine (choice C) and oral theophylline tablets (choice E) will not begin to work for at least 1/2 hour after administration.
Salmeterol inhalation (choice D) has an onset of action of around 20 minutes and has a duration of action of approximately 12 hours. Salmeterol is indicated for the "chronic" treatment/prevention of asthma signs and symptoms.

The correct answer is D. Charcot-Leyden crystals are distinctive hexagonal bipyramidal crystals composed of a protein (thought to function as a lysophospholipase) produced by eosinophils. They can be seen in settings in which tissue eosinophil counts are very high, including allergic conditions, asthma, and parasitic diseases. The sputum in asthma patients also typically shows large number of eosinophils, and may contain Curschmann spirals (mucus casts of smaller airways).
Bilirubin (choice A) can be found in gallstones.
Calcium phosphate (choice B), cystine (choice C), and uric acid (choice E) can be found in urinary tract stones; uric acid can also be found in crystals in tissues in patients with gout.

The correct answer is B. This item deals with the basic science principles underlying a common instruction given by physicians and pharmacists. Albuterol is a sympathomimetic bronchodilator with a rapid onset of action. Therefore, this medication is generally used several minutes before corticosteroids because it dilates the bronchioles and permits the passage of the corticosteroid deep into the lungs (choices A, C, and D are incorrect statements).
Flunisolide is an inhaled corticosteroid indicated for treatment of bronchial asthma when asthma is not controlled with bronchodilators and other non-steroidal medications. Oral fungal infections have occurred with continued use; therefore, patients should rinse out their mouth after each use (choice E is an incorrect statement). These agents are not to be used in treatment of acute asthma as single agents; children may experience HPA axis suppression with prolonged usage. Systemic effects include Cushing's syndrome, hyperglycemia, and glycosuria, and these agents may also cause burning, erythema, and oral dryness.

The correct answer is D. Montelukast is a selective and competitive leukotriene receptor antagonist that inhibits the cysteinyl leukotriene (CYSLT1) receptor. The CYSLT leukotrienes (LTC4, LTD4, and LTE4) are arachidonic acid derivatives that are released from a variety of cells, including mast cells and eosinophils. These leukotrienes bind to the CYSLT receptors in the airways. When these receptors are activated there is a strong correlation with the development of the signs and symptoms of asthma, including airway edema, smooth muscle contraction, and airway inflammation. Blockade of airway CYSLT receptors prevents this. It is indicated for the prophylactic and chronic treatment of asthma in adults and children > 6 years of age.
Bitolterol (choice A) is a beta2 agonist, and is able to relieve reversible bronchospasm by relaxing the smooth muscles of the bronchioles. It is indicated for the treatment for an acute asthma attack.
Cromolyn sodium (choice B) acts as an antiasthmatic and an antiallergic mast cell stabilizer. By inhibiting the degranulation of mast cells, this agent prevents the release of histamine and SRS-A (composed of leukotrienes). Asthma induced by inhalation of antigens can be inhibited by varying degrees with cromolyn pretreatments. This agent has no bronchodilator, antihistaminic, anticholinergic, or anti-inflammatory activity. It is indicated for prophylactic management of severe bronchial asthma, prevention of exercise induced bronchospasm, and prevention of allergic rhinitis.
Ipratropium (choice C) is an antimuscarinic agent that is structurally related to atropine. This agent is a quaternary amine (therefore, positively charged) and there is little systemic absorption. It is indicated for bronchospasm associated with COPD and rhinorrhea.
Theophylline (choice E) is a xanthine derivative medication that relaxes smooth muscle. The mechanism of action may be related to its ability to block adenosine receptors or to inhibit phosphodiesterase. Theophylline is indicated for the symptomatic relief/prevention of bronchial asthma (acute, childhood, nocturnal) as well as reversible bronchospasm associated with chronic bronchitis or emphysema.

The correct answer is A. Patients with disease of the small airways are generally not prescribed beta-receptor blocking agents since these agents can block the bronchodilation produced by endogenous and exogenous catecholamine stimulation of the beta2 receptors. However, relatively low doses of selective beta1 receptor blocking agents, such as atenolol and metoprolol, are relatively well tolerated.
All of the other answer choices are non-selective beta-receptor blocking agents and should not be used in this patient since they are likely to exacerbate the patient's condition.

Shortness Of Breath Case 1

Shortness Of Breath Case 1

A fire in a local factory brings patients to several hospitals with injuries. A 25-year-old woman is found by firefighters in a smoke-filled enclosed office. She has no apparent burns, but is complaining of shortness of breath and looks quite distressed. She is intubated in the emergency department for hypoxemia and admitted to the intensive care unit, where bronchoscopy reveals carbonaceous material in her large airways.

Where the bronchoscope camera exits the endotracheal tube, the resident, who has never performed a bronchoscopy before, notes that the rings of the airway are incomplete: the airway has "c-shaped" rings, and the remainder of the airway's circumference appears flat, with no clearly defined cartilaginous rings. Distal to the camera is a bifurcation. What is the significance of these findings?
/ A. The camera is in the trachea
/ B. The camera is in the trachea, but the rings are abnormal
/ C. The camera is in the left mainstem bronchus
/ D. The camera is in the right mainstem bronchus
/ E. There is not sufficient information to determine the location of the camera

18 hours after ICU admission, a chest x-ray shows bilateral diffuse airspace disease. Despite ventilation with 80% oxygen, her oxygen saturation is 90% and her arterial blood gas reveals a PO2 of 60, a PCO2 of 45, and a pH of 7.36. High airway pressures are required to generate small tidal volumes. What is the pathophysiology underlying this patient's hypoxic respiratory failure?
/ A. Abnormal alveolar capillary permeability
/ B. Acute bronchospasm
/ C. EIevated left atrial pressure
/ D. Rapidly progressive pulmonary fibrosis
/ E. Surfactant deficiency

Because of her poor pulmonary compliance, the decision is made to ventilate her using small tidal volumes and a high respiratory rate in order to maintain ventilation while avoiding the trauma potentially caused by very high airway pressures.
If her total minute ventilation remains constant, but her tidal volume decreases and respiratory rate increases, which of the following will occur?
/ A. Dead space increases
/ B. Dead space remains constant, but alveolar ventilation decreases
/ C. Dead space ventilation decreases and alveolar ventilation increases
/ D. Shunt decreases
/ E. Shunt remains the same, but alveolar ventilation improves

A change is made in her ventilator settings. The next arterial blood gas is: P02 60, PCO2 52, pH 7.30. Hemoglobin concentration is constant, as is the patient's temperature. What has happened to the total oxygen content of the blood and the oxygen saturation?
/ A. Arterial blood oxygen content and oxygen saturation has stayed the same
/ B. Arterial blood oxygen content has increased, but oxygen saturation has decreased
/ C. Arterial blood oxygen content has increased, and oxygen saturation has increased
/ D. Arterial blood oxygen content has decreased, and oxygen saturation has decreased
/ E. Arterial blood oxygen content has decreased, but oxygen saturation has increased

One week after admission, the patient develops fever to 39.4 C (103 F). A new dense infiltrate is seen in her right upper Iobe, and purulent secretions are suctioned from her endotracheal tube. Which of the following organisms is most likely causing a new ventilator-associated pneumonia?

/A.Borrelia burgdorferi

/B.Candida albicans

/C.Chlamydia pneumoniae

/D.Pneumocystis carinii

/E.Staphylococcus aureus


Shortness Of Breath Case 1 Answers

The correct answer is A. The only complete cartilaginous ring in the trachea is the cricoid cartilage of the larynx. The remainder of the tracheal cartilages are incomplete rings; they are nearly circumferential and maintain the patency of the trachea. The posterior wall of the trachea, directly anterior to the esophagus, is noncartilaginous and appears relatively flat. At the carina, the mainstem bronchi divide: the left mainstem bronchus exits at an angle to divide into left upper and lower lobes, and the right mainstem bronchus continues at a less acute angle off the trachea, where it quickly gives off a branch at an acute angle to the right upper lobe, then continues on to divide into branches to the right middle and lower lobes.
Choice B is incorrect because the tracheal rings are normally incomplete at their posterior aspect.
Choices C and D are incorrect because the cartilaginous rings of the mainstem bronchi are normally complete, thereby excluding the possibility that the camera is in a mainstem bronchus. The posterior membrane also localizes the camera in the trachea.
Choice E is incorrect because the posterior membrane of the trachea is unique to the trachea

The correct answer is A. This patient has the adult respiratory distress syndrome (ARDS), caused principally by alterations in capillary permeability. The normal blood-gas interface permits the transudation of water into the alveolus when the difference in hydrostatic pressure between the airspace and the capillary exceeds the plasma oncotic pressure. This interface, however, is not normally permeable to protein. With injury, whether direct toxic injury (as in this case) or due to inflammatory mediators and oxidative injury (in the case of sepsis), plasma proteins leak into the interstitial space and the airspace. This leaves the hydrostatic gradient unopposed and pulmonary edema ensues, despite normal hydrostatic pressures (i.e., in the absence of elevation of left atrial pressure).
Acute bronchospasm (choice B) can result from smoke inhalation. However, on chest x-ray films, this would appear as hyperinflated, abnormally radiolucent lungs. In addition, bronchospasm alone seldom results in this degree of hypoxemia.
Elevated left atrial pressure (choice C) causes cardiogenic pulmonary edema as the result of left heart failure, which is unlikely in this otherwise healthy 25-year-old who has sustained airspace injury as the result of inhalation of a toxic gas.
Pulmonary fibrosis (choice D) is a chronic disorder that can produce bilateral abnormalities on chest x-ray films, hypoxemia, and decreased pulmonary compliance. However, fibrosis as a pathologic process does not develop over hours and is not compatible with such an acute onset.
Surfactant deficiency (choice E) causes the neonatal respiratory distress syndrome, which is characterized by a similar clinical picture of decreased compliance, hypoxemia, and bilateral diffuse airspace disease. Surfactant has never been shown to be deficient in or beneficial in the treatment of ARDS.

The correct answer is B. Dead space (volume that is ventilated, but does not participate in gas exchange) remains constant, but with an increase in respiratory rate and a decrease in tidal volume, alveolar ventilation declines. That is, the amount of the minute ventilation that goes to the dead space increases:
Alveolar ventilation/min = (Tidal volume - Dead space volume) x Respiratory rate
As an example: a patient is breathing a tidal volume of 600 cc, 150 cc of which is dead space, at 12 x/minute. This translates into a total minute ventilation of 7.2 liters/min: alveolar ventilation/min is (600 cc-150 cc) x 12, or 5.4 liters/min. If her tidal volume decreases to 400 cc per breath, and she breathes at 18 breaths/min, minute ventilation is still 7.2 liters/min, but alveolar ventilation/min = (400 cc-150 cc) x 18 = 4.5 liters/min.
Choice A is incorrect because the dead space is not significantly altered by a drop in tidal volume.
Choice C is incorrect because dead space ventilation would increase. Before her ventilator was adjusted, dead space ventilation would be 1.8 L/min (150 cc x 12/min) and after the adjustment, it would be 2.7 L/min (150 cc x 18/min). And as shown above, alveolar ventilation would decrease.
Choice D is incorrect because with a drop in tidal volume, the shunt can remain the same or can actually increase, if the lower tidal volume results in closure of previously ventilated alveoli. (A shunt can be thought of as the opposite of dead space in the lung: an area that is perfused, but not ventilated.)
Choice E is incorrect because alveolar ventilation decreases (see above)

The correct answer is D. Arterial blood oxygen content has declined because of the rightward shift of the oxyhemoglobin dissociation curve. Arterial blood oxygen content is a function of hemoglobin concentration, of partial pressure of oxygen in the blood, and of the affinity of hemoglobin for oxygen. In this example, partial pressure of oxygen and hemoglobin concentrations are constant. Because of the lower pH and the higher CO2, however, the oxyhemoglobin dissociation curve has shifted to the right. That is, for a given partial pressure of oxygen, the hemoglobin saturation is lower. At higher concentrations of H+ ions, PCO2, temperatures, and concentrations of 2,3-DPG, hemoglobin has less affinity for oxygen. "A simple way to remember these shifts is that exercising muscle is acid, hypercarbic, and hot, and it benefits from increased unloading of O2 from its capillaries." (West, Respiratory Physiology, Chapter 6.)
Choices B and E are incorrect because oxygen saturation is the principal determinant of oxygen content. That is, the majority of the oxygen in the blood is carried bound to hemoglobin. As saturation declines, content declines.

The correct answer is E. Staphylococcus aureus is a gram-positive coccus that is a common cause of ventilator-associated pneumonia. It is a colonist of the skin and the nasopharynx, and is a common cause, not only of pneumonia (particularly ventilator-associated and post-influenza), but of endocarditis, superficial skin infections, surgical wound infections, and bacteremia (especially associated with indwelling catheters).
Borrelia burgdorferi(choice A) is a tick-transmitted spirochete that is responsible for Lyme disease. This disorder is characterized by erythema migrans in its early stage, followed by a variable presentation that can include malaise and fatigue accompanied by arthralgias, carditis, migratory musculoskeletal pain, meningitis, neuritis, chronic oligoarticular arthritis, and skin and neurological abnormalities.
Candida albicans(choice B) is a common yeast, which occasionally colonizes the upper airways of debilitated patients, but rarely is a cause of pneumonia. It is a common cause of vaginitis and can cause thrush, stomatitis, and esophagitis in immunosuppressed patients, and can cause bloodstream infections in patients with indwelling vascular appliances.
Chlamydia pneumoniae(choice C) is a common cause of community-acquired pneumonia as well as upper respiratory tract infection. Like all Chlamydia, it is an obligate intracellular parasitic bacterium.
Pneumocystis carinii(choice D) is an opportunistic pathogen (closely related to fungi and to protozoa), which causes pneumonia in hosts with compromised cellular immunity due to AIDS, corticosteroids, cancer chemotherapeutic agents, or primary defects of cellular immunity.