Valsalva maneuver
|
|
A Valsalva maneuver is any attempted exhalation against a closed glottis or against a closed mouth and nose. It is also known as Valsalva's test and Valsalva's method, after Antonio Maria Valsalva, a famous Italian anatomist. Valsalva's initial intention for the maneuver was as a method of expressing pus from the middle ear.
A Valsalva maneuver performed against a closed glottis results in a drastic increase in pressure in the thoracic cavity, the airtight section of the torso that houses the lungs and heart. In normal exhalation, the diaphragm contracts, pushing up and into the thoracic cavity. This increases pressure in the cavity and forces the air out of the lungs. However, when the air cannot escape, as when the glottis is closed in a Valsalva maneuver, pressure simply continues to build inside the thoracic cavity until the diaphragm relaxes or the air is allowed to escape. This reduces the amount of blood flow into the thoracic cavity, especially in the veins leading to the right atrium of the heart.
General uses
The Valsalva maneuver is used as a pressure equalisation technique by scuba divers and airplane passengers to avoid barotrauma and discomfort inside their ears when they move to a higher pressure breathing environment. It is also often used to aid in the expulsion of feces from the rectum during a bowel movement.
A person using this technique pinches their nose, closes their mouth and tries to exhale. The technique works by raising the pressure in the throat so that a small volume of air moves from the throat to the ears through the Eustachian tubes which connect them.
People inadvertently perform closed-glottis Valsalva maneuvers when blowing up a balloon or "bearing down" for a bowel movement. If the pressure is held for long enough, one will begin to feel as if pressure were building in the head, followed by dizziness and lightheadedness upon release of the maneuver.
Medical uses
A Valsalva maneuver increases vagal tone (parasympathetic) transiently. It can be used to try to correct the heart rhythm of someone in a supraventricular tachycardia, due to the effect of the increased vagal tone on the AV node of the heart.
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.
There are four phases of a Valsalva maneuver. Phase I is identified as the onset of expiration against the closed glottis. This is associated with a transient increase in the arterial pressure and decrease in the heart rate. This is followed by phase II, which is due to continued expiration against the closed glottis. There is a gradual decrease in the blood pressure during this phase, and the heart rate overshoots and goes above the baseline heart rate. Phase III is the end of expiration, in which the blood pressure decreased further. This is followed by phase IV, in which the blood pressure overshoots and goes above the baseline blood pressure.
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.