Abstract 103: Acute, Dose-Dependent, Blood Pressure-Lowering Effect of Continuous Positive Airway Pressure in Autonomic Failure Patients With Supine Hypertension

Abstract

Primary autonomic failure (AF) is characterized by disabling orthostatic hypotension but half of these patients also have supine hypertension. We have previously shown that continuous positive airway pressure (CPAP 4, 8, 12 and 16 cm H 2 O, each for 2 min) applied during autonomic blockade with trimethaphan acutely decreased systolic blood pressure (SBP) in hypertensive and normotensive subjects (-17±2 and -8±2 mmHg at 16 cm H 2 O) due to decreases in cardiac output (CO) and stroke volume (SV). In this study, we hypothesized that CPAP would have an acute, dose-dependent, blood pressure-lowering effect in patients with autonomic failure with supine hypertension. Five CPAP levels (0, 4, 8, 12 and 16 cm H 2 O, each for 2-3 min) were applied sequentially to 15 AF patients with supine hypertension (12 males, 70±1 yr). Hemodynamic parameters were measured at the end of each CPAP level. We found that CPAP levels of 4, 8, 12 and 16 cm H 2 O significantly decreased SBP in a dose-dependent manner (Figure). The maximal SBP drop was -20±3 mmHg with CPAP 16 (from 154±4 to 134±4 mmHg, P<0.01), and was associated with a decrease in CO (-12±4%) and SV (-13+4%). Neither systemic vascular resistance nor heart rate changed significantly with CPAP. SBP returned to baseline levels within 5 minutes after removal of the CPAP (REC). We conclude that, in AF patients with supine hypertension, CPAP acutely decreases SBP in a dose-dependent manner, due to decreases in CO and SV likely reflecting a decrease in venous return. These results suggest that CPAP could be used as a non-pharmacologic approach to treat the supine hypertension of AF. Future studies are needed to test the safety and efficacy of this approach.