(1) A forced expiration against a closed airway.
(2) The act of attempting to forcibly exhale while the nose and mouth are closed, or against a closed glottis.
When done properly, the abdomen and chest become contracted causing the gas pressure in the thoracic cavity to rise and the return of venous blood to the heart to decrease. When the airway is reopened, the blood pressure raises, the cardiac output increases, and eventually the heart beats more slowly by reflex. The maneuver may occur naturally during coughing, defecation, or gagging.
In medicine, it is used as a diagnostic tool in patients to test their heart conditions and to identify any abnormal heart rhythms. It is also applied to 'clear' the ears and sinuses. It is also taught to patients with multiple sclerosis to help them fully empty their bladder, and in sexual therapy to help men prevent premature ejaculation.
Variant: Valsalva maneuver, Valsalva's manoeuvre