Overnight Trials With Heat Stress in Autonomic Failure Patients With Supine Hypertension

Primary autonomic failure is a neurodegenerative condition characterized by loss of efferent sympathetic function and severe baroreflex impairment. The clinical hallmark of autonomic failure is disabling orthostatic hypotension, but at least half of patients are also hypertensive while lying down. This supine hypertension can be severe and associated with end-organ damage and worsening of orthostatic hypotension due to increased pressure natriuresis. It also complicates the management of these patients by limiting the use of daytime pressor agents for the treatment of orthostatic hypotension. Currently, no antihypertensive drug effectively lowers BP and prevents pressure natriuresis without worsening standing BP. It is well known that heat exposure (e.g. hot weather or a hot bath or shower) produces an acute and temporary worsening of orthostatic hypotension in autonomic failure patients. Factors that may predispose these patients to the lowering BP effects of heat stress include 1) impaired heat dissipation due to inability to sweat, 2) preserved heat-mediated skin vasodilation, and 3) blunted sympathetic hemodynamic responses to maintain BP (increases in cardiac output, heart rate, and vaso- and venoconstriction). Our preliminary results showed that 2 hours of passive heat stress lowers BP in these patients through a decrease in central volume. In this study, we will assess the efficacy and safety of passive heat stress in the treatment of nocturnal supine hypertension in autonomic failure patients. Our hypothesis is that controlled local (abdominal) passive heat stress applied during the night will lower nocturnal BP in autonomic failure patients with supine hypertension. To test this hypothesis, we propose to compare the BP effects of passive heat applied during the night vs. a sham control in a randomized crossover study in autonomic failure patients with supine hypertension.