REFLEX RESPONSES OF VENOUS CAPACITANCE VESSELS IN PATIENTS WITH HYPERTROPHIC CARDIOMYOPATHY

1. The aim of this study was to determine if there is impaired reflex venoconstriction in patients with hypertrophic cardiomyopathy and whet her this is related to a history of syncope or exercise hypotension. 2 . Thirty percent of patients with hypertrophic cardiomyopathy have exe rcise-induced hypotension associated with a failure of arteriolar cons triction. impaired venoconstriction could exacerbate this situation. 3 . We evaluated 43 patients with hypertrophic cardiomyopathy and 24 con trols. Nuclear venous plethysmography was used to measure forearm veno us capacitance during lower body negative pressure, splenic venous vol ume changes during bicycle exercise and blood pressure responses to tr eadmill exercise. We assessed any association between abnormal reflex venous control and a history of syncope and exercise hypotension. 4. T he percentage reduction in unstressed forearm venous volume during low er body negative pressure was similar in patients and controls (8.9 +/ - 7.1% versus 9.7 +/- 5.9%, P not significant). Patients with a histor y of syncope demonstrated a less marked percentage reduction in volume than those without (-2.1 +/- 6.9% versus -10.6 +/- 6.0%, P = 0.001), In three patients with a history of syncope there was a paradoxical in crease in forearm venous volume during lower body negative pressure. D uring exercise there was a substantially smaller decrease in splenic v enous volume in patients compared with controls (-20.1 +/- 14.0% and - 42.6 +/- 12.6% respectively, P = 0.0001), Furthermore, there was an as sociation between attenuated splenic venoconstriction or venodilation and exercise hypotension in patients (P = 0.005). 5. Abnormal reflex c ontrol of venous capacitance beds in patients with hypertrophic cardio myopathy was associated with both syncope and exercise hypotension.