[Clinical use of the Valsalva maneuver].

The Valsalva maneuver (VM) is a widely used test for autonomic nervous system function. It consists of a physiologic effort which is often performed in everyday life. Extreme effort may cause faintness or fainting, even in normal persons. The VM can help the physician manage loss of consciousness of unknown cause. Because of similarity of the effect of VM to that of hyperventilation on the cerebral circulation we suggest wider application of this maneuver in clinical electroencephalography.