Forearm vascular responses during orthostatic stress in control subjects and patients with posturally related syncope

The aim of this study was to compare the changes in forearm vascular resistance that occurred during orthostatic stress in asymptomatic volunteer subjects with those in patients with posturally related syncope. The authors hoped firstly that it would indicate the importance of vasoconstriction in the maintenance of blood pressure, and secondly that it might have diagnostic value if there were differences between symptomatic patients and asymptomatic volunteers. Twelve volunteers and 67 patients with unexplained syncope were classified as early or late fainters, based on their endurance of a test of combined head-up tilting and lower-body suction. Responses of vascular resistance were assessed from the ratio of arterial blood pressure (Finapres) to brachial artery blood velocity (Doppler). Changes in vascular resistance were greater in volunteers at all stages of the procedure than in patients. There was, however, no significant difference between the responses of early and late-fainting volunteers. These results demonstrate the importance of vasoconstriction in the resistance to posturally related syncope, and they indicate that assessments of responses of vascular resistance may improve the accuracy of the diagnosis.