Breath-Holding Physiology: Valsalva Maneuver Effects on Venous Return & Hemodynamics

Breath-holding (especially with glottis closed) increases intrathoracic pressure, altering venous hemodynamics.

Phases of Valsalva (Forced Expiration Against Closed Glottis)

1. Phase I (Onset): ↑ Intrathoracic pressure → ↑ aortic pressure (mechanical compression).
2. Phase II (Strain): ↓ Venous return → ↓ CO → ↓ BP → baroreflex → ↑ HR, vasoconstriction.
3. Phase III (Release): Sudden ↓ intrathoracic pressure → ↓ aortic pressure (transient).
4. Phase IV (Overshoot): Venous return surges → ↑ CO → ↑ BP (baroreflex) → reflex bradycardia.

Venous Effects

• Intrathoracic veins collapse → blood pools in extrathoracic veins (jugular distension, hepatic congestion).
• ↓ Preload → ↓ LV filling → ↓ stroke volume.

Clinical Uses

• Autonomic function testing (HR/BP response).
• Terminate SVT (vagal stimulation Phase IV).
• Murmur differentiation (HOCM ↑ murmur Phase II; AS/MR ↓).
• Weightlifting: Brief Valsalva stabilizes spine; prolonged → syncope risk.

Safety

Avoid prolonged straining if CVD, aneurysm, glaucoma, retinopathy. Exhale during exertion.