Cardiovascular and catecholamine changes induced by supine exercise and upright posture in vasovagal syncope. Comparisons with normal subjects and subjects with sympathetic denervation.

The haemodynamic and catecholamine responses to supine leg exercise were studied in vasovagal syncope (n = 10), pure autonomic failure (n = 10) and in control (n = 10) subjects. With exercise, blood pressure increased in controls; with a smaller rise in vasovagal syncope, and a substantial fall in pure autonomic failure. Heart rate increased similarly in controls and vasovagal syncope, but less in pure autonomic failure. The increase in cardiac index was less in controls and pure autonomic failure than vasovagal syncope; the fall in systemic vascular resistance was greatest in pure autonomic failure, but also fell more in vasovagal syncope than controls. Plasma noradrenaline levels increased in controls; with a smaller rise in vasovagal syncope and no increase in pure autonomic failure. Plasma adrenaline levels increased in vasovagal syncope only. The blood pressure responses to standing before and after exercise were similar in controls and vasovagal syncope, with no postural blood pressure fall; in pure autonomic failure there was a greater postural blood pressure fall post exercise. In conclusion, with supine exercise, blood pressure rose in controls and vasovagal syncope, and fell in pure autonomic failure. Systemic vascular resistance fell more in vasovagal syncope and pure autonomic failure, than controls. Noradrenaline responses differed and adrenaline rose in vasovagal syncope only. Standing post exercise did not induce syncope in vasovagal syncope, but increased postural hypotension in pure autonomic failure. There are clear differences in response to exercise in vasovagal syncope and pure autonomic failure. The differences between vasovagal syncope and control subjects suggest an underlying abnormality which may predispose to vasodepression in subjects with vasovagal syncope.