During the Valsalva maneuver (forced expiration against closed glottis), which of the following sequences correctly describes the cardiovascular changes during phase II (sustained straining)?

• A Increased intrathoracic pressure → decreased venous return → decreased CO → fall in BP → reflex tachycardia and peripheral vasoconstriction via baroreceptor reflex ✓
• B Increased intrathoracic pressure → increased venous return → increased CO and BP → reflex bradycardia
• C Decreased intrathoracic pressure → increased venous return → increased CO → rise in BP → reflex bradycardia
• D Increased intrathoracic pressure → direct cardiac compression → increased stroke volume → hypertension

Explanation

During phase II of the Valsalva maneuver, sustained straining raises intrathoracic pressure, compressing the vena cava and reducing venous return to the right heart. This decreases cardiac output and BP falls. Arterial baroreceptors (aortic arch and carotid sinus) detect this hypotension and trigger a sympathetic response: reflex tachycardia and peripheral arteriolar vasoconstriction. This is the basis for Valsalva testing of autonomic function — impaired tachycardia in phase II suggests cardiac sympathetic/parasympathetic neuropathy. Phase IV after release shows a pressure overshoot (due to persistent vasoconstriction now with restored venous return) and reflex bradycardia.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.