It is the act of exhaling
forcibly while keeping the respiratory tract closed. You might have
performed the Valsalva maneuver the last time you flew; it is easily
done by pinching your nose shut, sealing your lips, and trying
sharply to blow the air out of your lungs. This process builds
pressure in various parts of the body, including the abdomen, which
is why you might also engage in a version of the Valsalva maneuver
on the toilet. The technique provides relief from the blocking
sensation caused by high external air pressures in an aircraft
cabin.
The Valsalva maneuver is a diagnostic tool for detecting certain
kinds of cardiac abnormalities, as it changes venous and arterial
pressure in ways that reliably affect the intensity of various heart
murmurs. In some cases, it is also a medical intervention; it often
halts episodes of tachycardia (abnormally fast heart rate).
Named after the 18th-century Italian anatomist Antonio Maria
Valsalva, who offered the first formal description of the maneuver.