A 64-year-old man with a long-standing history of hypertension is brought to the emergency department with a dry cough and shortness of breath. The patient has been unable to sleep in the flat position for the past 2 days. Blood pressure is 192/102 mm Hg and pulse is 92/min and regular. Physical examination reveals an S4 and bibasilar crackles. He is started on intravenous nitroglycerin infusion and soon after reports significant symptomatic relief. Which of the following physiologic changes are most likely to occur following administration of this medication?

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This patient's clinical presentation is consistent with acute pulmonary edema due to severely elevated blood pressure (hypertensive emergency). Intravenous vasodilators (eg, nitroglycerine, sodium nitroprusside) are often used in management of acute heart failure due to severe hypertension. Nitrates are primarily venodilators that increase peripheral venous capacitance, thereby reducing cardiac preload and left ventricular end-diastolic pressure (LVEDP) and volume. This is the primary mechanism of action for symptom relief in patients with acute pulmonary edema. Lower LVEDP also leads to a reduction in LV systolic wall stress and a decrease in myocardial oxygen demand, resulting in relief of angina symptoms. Although the vasodilatory effects of nitrates act primarily on the venous system, they also have a modest effect on arteriolar dilation. Higher doses can lead to a significant drop in systemic blood pressure, thereby decreasing cardiac afterload, reducing left ventricle wall stress, and causing a further decrease in myocardial oxygen demand. Educational objective: Nitrates are primarily venodilators and increase peripheral venous capacitance, thereby reducing cardiac preload and left ventricular end-diastolic volume and pressure. Nitrates also have a modest effect on arteriolar dilation and cause a decrease in systemic vascular resistance and cardiac afterload. __________ References: Mechanisms of action of nitrates. (http://www.ncbi.nlm.nih.gov/pubmed/7873467)

A 64-Year-Old Man with a Long-Standing History of Hypertension Is