Most people do Valsalva maneuvers inadvertently when blowing up balloons.
A Valsalva maneuver can be useful for equalising the pressure in your inner ear with the outside, especially when the pressure outside changes rapidly as during airplane descents or during diving.
Medical uses of the Valsalva maneuver
A Valsalva maneuver also increases vagal tone (parasympathetic) transiently. It is worthwhile trying out a Valsalva to see if it will correct the heart rhythm of someone in supraventricular tachycardia.
Doing a Valsalva maneuver causes a transient lowering in ventricular filling and thus reduces the intensity of most cardiac murmurs. There are two exceptions to this rule, these being the murmur of hypertrophic cardiomyopathy and the murmur of mitral valve prolapse, which paradoxically become louder during a Valsalva maneuver.
Harrison's principles of Internal Medicine classifies four stages of a Valsalva maneuver, these being I - onset of expiration, II - continued expiration against a closed glottis, III - end of expiration and IV - recovery and describes how the blood pressure and heart rate change during these phases. In a normal person, the heart rate decreases in phase I, increases in phase II and III and decreases in phase IV.
Some cardiologists measure the Valsalva ratio which is the maximum heart rate in phase II over the minimum heart rate in phase IV of the Valsalva Maneuver.