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 we re studied in vasovagal syncope (n=10), pure autonomic failure (n=10) and in control (n=10) subjects. With exercise, blood pressure increase d in controls; with a smaller rise in vasovagal syncope, and a substan tial fall in pure autonomic failure. Heart rate increased similarly in controls and vasovagal syncope, but less in pure autonomic failure. T he increase in cardiac index was less in controls and pure autonomic f ailure than vasovagal syncope; the fall in systemic vascular resistanc e was greatest in pure autonomic failure, but also fell more in vasova gal syncope than controls. Plasma noradrenaline levels increased in co ntrols; with a smaller rise in vasovagal syncope and no increase in pu re autonomic failure. Plasma adrenaline levels increased in vasovagal syncope only. The blood pressure responses to standing before and afte r exercise were similar in controls and vasovagal syncope, with no pos tural blood pressure fall; in pure autonomic failure there was a great er postural blood pressure fall post exercise. In conclusion, with sup ine exercise, blood pressure rose in controls and vasovagal syncope, a nd fell in pure autonomic failure. Systemic vascular resistance fell m ore in vasovagal syncope and pure autonomic failure, than controls. No radrenaline responses differed and adrenaline rose in vasovagal syncop e only. Standing post exercise did not induce syncope in vasovagal syn cope, but increased postural hypotension in pure autonomic failure, Th ere 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 pred ispose to vasodepression in subjects with vasovagal syncope.