The Valsalva maneuver involves forcible exhalation against a closed glottis after full inspiration, causing increased intrathoracic pressure. The normal systolic blood pressure response follows four phases: (1) transient increase during onset of the "strain" phase when the patient bears down, due to increased intrathoracic pressure; (2) sharp decrease to below baseline as the "strain" phase is maintained, due to decreased venous return; (3) further acute drop of both blood pressure and left ventricular volume during the "release" phase, due to decreased intrathoracic pressure; and (4) "overshoot" increased blood pressure, due to reflex sympathetic activation and increased stroke volume.This maneuver has several uses at the bedside.

To distinguish the murmur of hypertrophic cardiomyopathy, ask the supine patient to "bear down, like straining during a bowel movement." Alternatively, place one hand on the patient's midabdomen and ask the patient to strain against it. With your other hand, place your stethoscope on the patient's chest and listen at the lower left sternal border.

The Valsalva maneuver can also identify heart failure and pulmonary hypertension. Inflate the blood pressure cuff to 15 mm Hg greater than the systolic blood pressure and ask the patient to perform the Valsalva maneuver for 10 seconds, then resume normal respiration. Keep the cuff pressure locked at 15 mm Hg above the baseline systolic pressure during the entire maneuver and for 30 seconds afterward. Listen for Korotkoff sounds over the brachial artery throughout. Typically, only phases 2 and 4 are significant, since phases 1 and 3 are too short for clinical detection. In healthy patients, phase 2, the "strain" phase, is silent; Korotkoff sounds are heard after straining is released during phase 4.

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