Arterial baroreflex control of sympathetic nerve activity in multiple sclerosis

Abstract

Up to 50% of patients with multiple sclerosis (MS) experience symptoms of orthostatic intolerance. The aim of this study was to determine if this higher incidence is potentially due to altered arterial baroreflex (ABR) control of muscle sympathetic nerve activity (MSNA) or heart rate (HR). Five patients with relapsing‐remitting MS (4 females/1 male) and 3 healthy age‐matched controls (2 females/1 male) were instrumented for MSNA, arterial blood pressure (Finometer), and HR. ABR gain was calculated from linear regression slopes of both MSNA (relative burst amplitude) and HR plotted against diastolic and systolic pressure (3‐mmHg bins), respectively, during venous administration of sodium nitroprusside followed by phenylephrine (i.e., modified Oxford technique). Baseline burst frequency (number of bursts/min; BF) and burst incidence (number of bursts/100 heartbeats; BI) were significantly lower (P<0.01) in MS patients (BF=5±1, BI =8±1;n=5) compared to controls (BF=25±10, BI=41±13;n=3). ABR control of MSNA may be attenuated (P=0.09) in MS patients (gain=‐1.1±0.7; n=4) compared to controls (gain=‐2.1±0.7; n=3). ABR control of HR is similar (P=0.61) in MS patients (gain=‐0.7±0.3; n=5) and controls (gain=‐0.6±0.4; n=3). These initial findings suggest that impaired ABR control of MSNA may contribute to the higher incidence of orthostatic intolerance in MS patients.Funded by National MS Society (PP1440)