This is carried out by closing the mouth, holding the nose and attempting to blow hard. The manoeuvre raises pressure in the chest – and, indirectly, the abdomen – and forces air from the back of the nose down the EUSTACHIAN tube to the middle ear. This latter effect can be used to clear the tube during descent in an aircraft, when it sometimes becomes blocked or partially blocked, producing differential pressures on the two sides of the eardrum, usually accompanied by temporary pain and deafness.

Valsalva's manoeuvre is involuntarily performed when a person strains to open his or her bowels: in these circumstances the passage of air to the lungs is blocked by instinctive closure of the vocal cords in the LARYNX. The resultant raised abdominal pressure helps to expel the bowel contents. The manoeuvre is also used in the study of cardiovascular physiology because the rise in pressure in the chest restricts the return of venous blood to the right atrium of the HEART. Pressure in the peripheral VEINS is raised and the amount of blood entering and leaving the heart falls. This drop in cardiac output may cause the subject to faint because the supply of oxygenated blood to the brain is reduced. It is also sometimes performed by schoolchildren for their own and friends’ entertainment.