26/08/2026
MCQ of the Day, Physiology.
During moderate exercise, cardiac output rises several-fold while mean arterial pressure rises only slightly. Which of the following best explains this?
A) A fall in total peripheral resistance from skeletal muscle vasodilation
B) A rise in total peripheral resistance from sympathetic vasoconstriction
C) A fall in stroke volume offsetting the rise in heart rate
D) Baroreceptor-mediated reduction in heart rate
Answer: A, a fall in total peripheral resistance from skeletal muscle vasodilation. Mean arterial pressure is the product of cardiac output and total peripheral resistance. In exercise, local metabolic vasodilation in active skeletal muscle opens a very large vascular bed, so total peripheral resistance falls sharply. Cardiac output rises through both heart rate and stroke volume, but because resistance falls at the same time, the product changes far less than cardiac output alone would suggest, and mean arterial pressure rises only modestly. Sympathetic vasoconstriction does occur, but in non-exercising beds such as splanchnic and renal circulation, where it redistributes flow rather than raising overall resistance. Stroke volume rises in exercise, it does not fall, and baroreceptor activity is reset upward in exercise rather than slowing the heart.
Ref: Ganong's Review of Medical Physiology, Cardiovascular Regulatory Mechanisms chapter.
