Modifications of autonomic activity and baroreceptor response during tilt-induced vasovagal syncope

Vasovagal syncope (WS) is diagnosed by medical history and confirmed by head-up tilt (HUT) test. In this study, we attempted to examine this controversy by evaluating heart rate variability and baroreceptor sensitivity in WS during upright posture. The WS subjects had lower total peripheral vascular resistance at baseline supine and HUT position. During HUT test, the WS subjects had increased LF/HF ratio and decreased baroreceptor sensitivity. In conclusion, WS subjects demonstrated vascular sympathetic dysfunction and postural cardiac sympathetic hyperactivity. The decreased baroreceptor sensitivity may explain in part the failure of the usual compensatory heart rate increase during orthostatic challenge.