Head-up tilt for triggering and diagnosing syncope.

Head-up tilt to 70 degrees lasting for 30 min is a further useful test for studying syncope. In 26.69% of 109 consecutive out-patients referred for loss of consciousness, it induced vasodepressor and/or cardioinhibitory reactions. All symptomatic patients had similar EEG changes and blood pressure fall during symptoms: by contrast, ECG features, due to vagal activation, were different. The pathogenetic mechanism of vasovagal or vasodepressor syncope is an abrupt sympathetic cardiovascular inhibition with more or less marked vagal cardiac activation. This cardiovascular pattern is due to a cardiac reflex in orthostatic syncope or, probably, to a central activation in emotional fainting.