A 45-year-old hypertensive patient undergoes valsalva maneuver. In phase II of the Valsalva maneuver, which hemodynamic change occurs?
- A Increased intrathoracic pressure augments venous return → increased cardiac output → reflex bradycardia
- B Blood pressure rises acutely and remains elevated throughout phase II
- C Increased intrathoracic pressure reduces venous return → fall in cardiac output → reflex tachycardia and vasoconstriction ✓
- D Heart rate falls due to direct compression of the SA node during bearing down
Explanation
Phase II of the Valsalva maneuver (sustained strain): elevated intrathoracic pressure impedes venous return to the right heart, reducing preload and cardiac output, causing blood pressure to fall. The baroreceptor reflex is activated → sympathetic stimulation → reflex tachycardia, increased myocardial contractility, and peripheral vasoconstriction. In phase II late, blood pressure begins to recover toward baseline due to vasoconstriction. Phase IV (after release): venous return suddenly restored → overshoot hypertension → reflex bradycardia. Absence of this square-wave response in heart failure patients (fixed output) aids diagnosis.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.