A 64-year-old man with heart failure with reduced ejection fraction (ejection fraction 30%) is started on a guideline-directed medication after his symptoms remain limited despite an angiotensin-converting enzyme inhibitor and a diuretic. Over the following weeks his resting heart rate decreases from 88/min to 64/min, his blood pressure decreases modestly, and his exercise tolerance improves. He reports no episodes of bronchospasm. The newly added drug improves long-term survival in part by reducing myocardial oxygen demand and attenuating chronic adrenergic stimulation of the heart.

Which of the following best describes the mechanism of action of the newly added drug?

A 52-year-old man with hypertension and type 2 diabetes with albuminuria is started on a drug that lowers blood pressure and is renoprotective. Two weeks later, laboratory studies show a mild increase in serum creatinine and serum potassium and a marked rise in plasma renin activity. He develops a persistent dry cough. The drug exerts its effect by reducing the conversion of a circulating peptide to its active form.

The drug given to this patient most directly inhibits which of the following?

A 38-year-old man who has never smoked presents with progressive dyspnea. CT of the chest shows emphysematous changes most prominent at the lung bases (panacinar pattern). He also has mildly elevated liver enzymes, and a liver biopsy shows hepatocytes containing PAS-positive, diastase-resistant cytoplasmic globules. Pulmonary function testing shows an obstructive pattern.

The pulmonary destruction in this patient is best explained by which of the following mechanisms?

A 70-year-old woman with paroxysmal atrial fibrillation and a structurally normal heart is started on an antiarrhythmic drug to maintain sinus rhythm. The drug acts primarily on the ventricular myocyte action potential by blocking the rapid component of the delayed rectifier potassium current (I_Kr). Her follow-up ECG shows a prolonged QT interval, and she is counseled about the risk of torsades de pointes.

Which phase of the cardiac ventricular action potential is most directly prolonged by this drug?

A 19-year-old woman with persistent asthma and aspirin-exacerbated respiratory disease has frequent symptoms despite an inhaled corticosteroid. She is started on an oral agent that reduces the synthesis of all leukotrienes by inhibiting the enzyme that converts arachidonic acid to the unstable intermediate leukotriene A4. She is counseled that periodic monitoring of liver function tests is required.

The drug started in this patient most likely inhibits which of the following enzymes?

A 55-year-old woman develops sudden pleuritic chest pain and dyspnea two days after a 14-hour intercontinental flight. She recently completed a course of estrogen-containing therapy and had right knee surgery three weeks ago. Her right calf is swollen and tender. CT pulmonary angiography confirms a filling defect in a segmental pulmonary artery.

The combination of risk factors in this patient promotes thrombosis primarily through which classic triad of mechanisms?

A physiology study measures regional ventilation and perfusion in a healthy upright adult breathing room air. Both ventilation and perfusion are greater at the lung base than at the apex, but perfusion increases more steeply from apex to base than ventilation does. The investigators calculate the ventilation/perfusion (V/Q) ratio at different vertical levels of the lung.

Compared with the lung base, the apex of the upright lung is best characterized by which of the following?

A 5-year-old boy develops periorbital and lower-extremity edema over several days. Urinalysis shows 4+ proteinuria (urine protein 5.5 g/day) without hematuria. Serum albumin is low and serum cholesterol is elevated. Blood pressure is normal. Light microscopy of a renal biopsy is unremarkable, immunofluorescence is negative, and electron microscopy shows diffuse effacement of podocyte foot processes.

Which of the following best characterizes the underlying glomerular abnormality in this patient?

A 58-year-old man with a 30-pack-year smoking history, hypertension, and an LDL cholesterol of 190 mg/dL dies of a myocardial infarction. At autopsy, the coronary arteries contain raised intimal plaques. Microscopic examination of an early lesion shows numerous large cells with abundant lipid-filled, foamy cytoplasm beneath the endothelium, along with extracellular lipid and proliferating smooth muscle cells.

The foamy cells in this lesion are most likely derived from which of the following?

A 72-year-old woman is admitted with fever, hypotension (blood pressure 80/40 mm Hg), and warm extremities after a urinary tract infection. Pulmonary artery catheterization shows a cardiac output of 9 L/min (elevated), a low systemic vascular resistance, and a normal-to-low pulmonary capillary wedge pressure. Her skin is flushed and warm.

Which of the following best explains the hemodynamic profile in this patient?