Altered respiratory related bursting of muscle sympathetic nerve activity in humans with essential hypertension

Abstract

Elevation in the respiratory modulation of sympathetic activity contributes to the elevated vascular resistance and blood pressure (BP) in spontaneously hypertensive rats. It is presently unclear whether respiratory related fluctuations in muscle sympathetic nerve activity (MSNA) are altered in human essential hypertension. To investigate this, multiunit recordings of postganglionic MSNA (microneurography) were obtained in hypertensive patients (n=10, 62±2 years) and normotensive controls (n=6, 59±2 years with comparable BMI (~27 kg·m2). Respiratory movements (strain gauge pneumobelt), heart rate (HR; ECG) and BP (Finometer) were monitored while subjects lay supine, breathing normally. After correcting for nerve conduction delays respiratory cycle triggered averaging of MSNA was performed. Mean BP was higher in the hypertensive group (106±2 vs. 83±3 mmHg, P<0.05), while HR was similar between groups. Notably, MSNA burst incidence (i.e. percentage of cardiac cycles associated with a MSNA burst) during the inspiratory to post-inspiratory period tended to be greater in hypertensives than controls (39±6 vs. 20±5 bursts·100 heart beats−1; P=0.058), but was similar in both groups during mid-to-late expiration (P=0.464). These data suggest that the cyclic inhibition of MSNA during respiration is attenuated in patients with essential hypertension.