Valsalva Maneuver

Editor – I enjoyed the article “Antonio Maria Valsalva (1666 – 1723)”¹ and would like to add that as well as diagnosing cardiac conditions, the Valsalva maneuver is also part of the autonomic testing battery. There are two specific autonomic components:

1. Valsalva ratio: this is the ratio of heart rate phase IV/heart rate phase II, and is essentially a measure of vagal function. The normal response is an increase in heart rate during phase II in response to the fall in blood pressure, and the baroreflex response to the blood pressure overshoot in phase IV is transient bradycardia. In dysautonomic patients, there is typically a loss of both the blood pressure overshoot and the reflex bradycardia. Age-adjusted normal Valsalva ratios are used as controls for the Valsalva ratio.

2. Beat-to-beat blood pressure response to the Valsalva maneuver: phase II may be divided into early and late phases. In early phase II, reduced preload and stroke volume lead to a fall in cardiac output despite the tachycardia caused by decreased vagal activity. Total peripheral resistance increases due to increased sympathetic discharge (nucleus tractus solitarius) and an increase in plasma epinephrine concentration. The fall in blood pressure is thus arrested, and is termed “late phase II”; in normal patients there is actually a rise in blood pressure just before release. Interestingly, this phase can be blocked with alpha-antagonists (e.g., phentolamine) while phase IV can be blocked with beta-blockers.

Patients with peripheral adrenergic failure due to involvement of autonomic fibers will have absent late phase II and in fact can have such dramatic drops in blood pressure during forced expiration that syncope may occur.