A healthy volunteer stands up suddenly from a lying position. Within seconds, which set of cardiovascular changes occurs via the arterial baroreceptor reflex?

• A Increased heart rate, decreased contractility, increased stroke volume
• B Decreased heart rate, increased vagal tone, increased stroke volume
• C Increased heart rate, increased sympathetic tone, reduced stroke volume from lower preload ✓
• D No change in heart rate, increased total peripheral resistance alone

Explanation

Standing pools blood in the legs, lowering venous return and arterial pressure. Reduced baroreceptor firing withdraws vagal tone and increases sympathetic output, raising heart rate and contractility. Stroke volume actually falls initially because preload drops with the reduced venous return, and this fall persists despite the reflex response. Option A fails because contractility rises with sympathetic stimulation, and option D fails because the reflex adjusts both rate and vascular resistance together.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.