What is the effect of increased sympathetic tone on dP/dt_max and stroke volume?

• A. dP/dt_max increases due to enhanced contractility; stroke volume may increase via higher contractility and venous return.
• B. dP/dt_max decreases as sympathetic tone increases.
• C. dP/dt_max remains unchanged; stroke volume always increases.
• D. dP/dt_max increases but stroke volume decreases.

Answer: (A)

When the sympathetic nervous system is more active, the heart becomes more contractile and the veins constrict, which both feed into higher stroke output. The maximum rate at which the ventricle generates pressure during its rise (dP/dt_max) goes up because contractility is enhanced: more calcium is available in the heart muscle cells, cross-bridge cycling speeds up, and pressure climbs more rapidly. That sharper, faster rise in pressure reflects a stronger inotropic state.

Stroke volume tends to rise as a result of two complementary effects: stronger contractility couples with the heart’s ability to eject more of its end-diastolic volume, and venoconstriction increases venous return, raising preload. With higher preload and enhanced contractility, the amount ejected per beat can increase. In some situations, afterload from vasoconstriction can temper this effect, but the overall pattern with increased sympathetic tone is an increase in dP/dt_max and a tendency for stroke volume to rise.