During exercise, a healthy 25-year-old's systolic BP rises to 180 mmHg but diastolic remains 80 mmHg. The mechanism responsible for the maintained diastolic pressure despite markedly increased cardiac output is:
- A Baroreceptor reflex increasing systemic vascular resistance to compensate
- B Increased venous return elevating end-diastolic volume and thus diastolic pressure
- C Splanchnic vasoconstriction maintaining diastolic pressure
- D Marked vasodilation in exercising muscle beds reducing TPR, offsetting the increased cardiac output's effect on diastolic pressure ✓
Explanation
During aerobic exercise, cardiac output can increase 4–6 fold, but diastolic BP remains stable or rises only modestly because total peripheral resistance falls proportionally due to marked vasodilation in active skeletal muscle. Mean arterial pressure = CO × TPR; since TPR falls as CO rises, MAP increases only modestly. The widened pulse pressure (high systolic, relatively stable diastolic) reflects increased stroke volume and ejection velocity. Baroreceptors are actually reset to tolerate higher pressures during exercise; splanchnic and renal vasoconstriction do occur but are not the primary reason diastolic is maintained—the dominant effect is working muscle vasodilation.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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