The Cardiac Vagal Response to Water Ingestion in Normal Human Subjects

In healthy young subjects there is direct evidence for sympathetic vasoconstrictor activation after drinking water, but this is not accompanied by an increase in arterial blood pressure. A marked pressor response to water ingestion has, however, been observed in elderly subjects and in patients with autonomic failure. We examined the effect of water ingestion on haemodynamic variables and heart rate variability (HRV) markers of cardiac vagal control in ten healthy young subjects and four cardiac transplant recipients with confirmed persistent cardiac vagal denervation. In a random order crossover protocol, changes in heart rate, blood pressure and measures of high frequency (HF) HRV were compared over time following the ingestion of 500 ml and 20 ml (control) of tap water. In healthy subjects, after drinking 500 ml of water the heart rate fell from 67.6+/-2.0 (mean+/-S.E.M.) to 60.7+/-2.4 beats/min (P