Abstract 022: Blood Pressure-Lowering Effect of Local Passive Heat in Autonomic Failure Patients with Supine Hypertension

Abstract

Primary autonomic failure (AF) is characterized by disabling orthostatic hypotension that is acutely worsened by environmental heat. Given that about half of AF patients have paradoxical supine hypertension, we hypothesized that controlled local passive heat would lower supine blood pressure (BP) in these patients. Fourteen AF patients with supine hypertension (age 71±2 years, 9 men, systolic BP 172±6 mmHg) were randomized to receive passive heat (40-42°C, commercial heating pad over abdomen and pelvis) and sham control for up to 2 hours in a 2-day crossover study. Hemodynamic parameters and core body and skin temperatures were measured in the supine position. The heating pad increased abdominal skin temperature to 40.8±0.4°C and 40.1±0.3°C after 1 and 2 hours of passive heat (vs 35.2±0.2°C and 35.1±0.4°C in sham controls). Core body temperature increased after 1 hour (by 0.2±0.1°C [to 36.9±0.8°C] vs 0.0°C [36.7±0.1°C] in sham controls; P=0.04) and 2 hours (by 0.4±0.1°C [to 37.2±0.1°C] vs 0.1±0.03°C [to 36.8±0.1°C] in sham controls; P=0.04). Systolic BP decreased during heat stress compared to sham control (P<0.01 by mixed-effects model) with a maximal reduction at 1.7 hours of -26±5 mmHg (Figure). This BP drop was due to a decrease in cardiac output (-30±5% vs sham -5±3%; P=0.02) and stroke volume (-29±5% vs sham -6±3%; P<0.01). Systemic vascular resistance and heart rate were similar in both groups. In conclusion, low levels of local passive heat had a BP-lowering effect in AF patients with supine hypertension presumably due to an uncompensated decrease in central blood volume. The therapeutic application of this approach needs to be addressed in future studies.