Sympathetic neural and hemodynamic responses to upright tilt in elderly African Americans versus Caucasians

Abstract

It has been demonstrated that neural control of blood pressure (BP) is different in young African Americans (AA) and Caucasians (CAU). Whether this is also true in elderly people is unclear. We tested the hypothesis that elderly AA have enhanced sympathetic neural responses during orthostasis compared with elderly CAU. Muscle sympathetic nerve activity (MSNA), BP, and heart rate (HR) were recorded continuously, cardiac output (Qc, C2H2 rebreathing), stroke volume (SV=Qc/HR) and total peripheral resistance (TPR=mean BP/Qc) were measured intermittently supine and during 5‐min 60‐degree upright tilt in 10 AA [6 M, 4F; 65±4 (SD) yrs] and 15 CAU (9M, 6 F; 67±4 yrs). AA and CAU had similar supine (44±10 vs 42±8 bursts/min) and upright MSNA burst frequency (59±11 vs 60±11 bursts/min; P=0.98 for race, <0.01 for posture, 0.58 for interaction). However, upright total MSNA was smaller in AA than CAU (162±39 vs 248±126%; P<0.01). Systolic BP, HR, Qc and SV were not different between groups in the supine position and during upright tilt. Supine diastolic BP was similar between groups (66±7 vs 65±8 mmHg; P=0.76), but upright diastolic BP was greater in AA than CAU (80±10 vs 71±8 mmHg; P=0.02). TPR did not differ between AA and CAU in both supine (1536±295 vs 1741±401 dyn·s·cm−5) and upright postures (2490±555 vs 2522±886 dyn·s·cm−5; P=0.47 for race, <0.01 for posture, 0.71 for interaction). These results suggest that elderly African Americans have a blunted sympathetic neural responsiveness but enhanced blood pressure reactivity during orthostasis compared with elderly Caucasians, which may be attributable to an augmented sympathetic vascular transduction.Supported by NIH R01 HL091078.