During phase IV of the Valsalva maneuver in a normal subject, arterial pressure rises above baseline and heart rate falls below baseline. This overshoot results chiefly from:

• A Baroreflex response to restored venous return and increased stroke volume ✓
• B Sustained elevated intrathoracic pressure compressing the aorta
• C Peripheral chemoreceptor activation by transient hypoxia
• D Residual sympathetic withdrawal persisting from strain phase

Explanation

On release of the strain, intrathoracic pressure normalizes and pooled venous blood suddenly returns to the heart, raising cardiac output and arterial pressure above resting levels. Intact baroreceptors sense this overshoot and reflexly slow the heart through vagal discharge, producing bradycardia. The four-phase Valsalva response is therefore a standard bedside test of autonomic function. Elevated intrathoracic pressure ends at the moment of release, and chemoreceptors play no role in this mechanical sequence.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.