Sympathetic Baroreflex Sensitivity in Normotensive Pregnant Women

Abstract

Muscle sympathetic nerve activity (MSNA) is increased during pregnancy while mean arterial pressure (MAP) is maintained or reduced, suggesting baroreflex resetting. We hypothesized that sympathetic baroreflex sensitivity (BRS) would be reduced in normotensive pregnant women (PREG) relative to similarly aged non-pregnant controls (CTRL). Integrated MSNA burst incidence (microneurography), MAP and diastolic blood pressure (DBP; Finometer), cardiac output (Q; ModelFlow), and total peripheral resistance (TPR; MAP/Q) were assessed at rest in 11 PREG (33±1 weeks gestation, 31±1y, pre-pregnancy BMI: 24±1 kg/m2) and 10 CTRL (29±1y; BMI: 25±2). MSNA was higher in PREG than CTRL (43±2 vs 33±2 bursts/100hb, P<0.01) while DBP was similar between groups, indicating an upward resetting of the BRS set-point in PREG. Spontaneous BRS slope, calculated from the linear relationship between MSNA burst incidence and DBP, was reduced in PREG vs CTRL (-5.3±0.5 vs -3.7±0.5 bursts/100hb/mmHg). PREG was also associated with a blunting of neurovascular transduction (TPR/MSNA) relative to CTRL (0.28±0.01 vs 0.45±0.03 a.u., P<0.01), resulting in the maintenance of normal MAP in PREG. Supported by WCHRI, NSERC & University of Alberta Human Performance Scholarship Fund.