title: Sympathetic baroreflex gain in normotensive pregnant women.
abstract: Muscle sympathetic nerve activity is increased during normotensive pregnancy while mean arterial pressure is maintained or reduced, suggesting baroreflex resetting. We hypothesized spontaneous sympathetic baroreflex gain would be reduced in normotensive pregnant women relative to nonpregnant matched controls. Integrated muscle sympathetic burst incidence and total sympathetic activity (microneurography), blood pressure (Finometer), and R-R interval (ECG) were assessed at rest in 11 pregnant women (33 ± 1 wk gestation, 31 ± 1 yr, prepregnancy BMI: 23.5 ± 0.9 kg/m(2)) and 11 nonpregnant controls (29 ± 1 yr; BMI: 25.2 ± 1.7 kg/m(2)). Pregnant women had elevated baseline sympathetic burst incidence (43 ± 2 vs. 33 ± 2 bursts/100 heart beats, P = 0.01) and total sympathetic activity (1,811 ± 148 vs. 1,140 ± 55 au, P < 0.01) relative to controls. Both mean (88 ± 3 vs. 91 ± 2 mmHg, P = 0.4) and diastolic (DBP) (72 ± 3 vs. 73 ± 2 mmHg, P = 0.7) pressures were similar between pregnant and nonpregnant women, respectively, indicating an upward resetting of the baroreflex set point with pregnancy. Baroreflex gain, calculated as the linear relationship between sympathetic burst incidence and DBP, was reduced in pregnant women relative to controls (-3.7 ± 0.5 vs. -5.4 ± 0.5 bursts·100 heart beats(-1)·mmHg(-1), P = 0.03), as was baroreflex gain calculated with total sympathetic activity (-294 ± 24 vs. -210 ± 24 au·100 heart beats(-1)·mmHg(-1); P = 0.03). Cardiovagal baroreflex gain (sequence method) was not different between nonpregnant controls and pregnant women (49 ± 8 vs. 36 ± 8 ms/mmHg; P = 0.2). However, sympathetic (burst incidence) and cardiovagal gains were negatively correlated in pregnant women (R = -0.7; P = 0.02). Together, these data indicate that the influence of the sympathetic nervous system over arterial blood pressure is reduced in normotensive pregnancy, in terms of both long-term and beat-to-beat regulation of arterial pressure, likely through a baroreceptor-dependent mechanism.
authors.affiliation: Program for Pregnancy and Postpartum Health, Physical Activity and Diabetes Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Canada; Alberta Diabetes Institute, Women and Children's Health Research Institute, and.
authors.forename: Charlotte W
authors.initials: CW
authors.lastname: Usselman
authors.affiliation: Program for Pregnancy and Postpartum Health, Physical Activity and Diabetes Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Canada; Alberta Diabetes Institute, Women and Children's Health Research Institute, and.
authors.forename: Rachel J
authors.initials: RJ
authors.lastname: Skow
authors.affiliation: Program for Pregnancy and Postpartum Health, Physical Activity and Diabetes Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Canada; Alberta Diabetes Institute, Women and Children's Health Research Institute, and.
authors.forename: Brittany A
authors.initials: BA
authors.lastname: Matenchuk
authors.affiliation: Department of Obstetrics and Gynecology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Canada;
authors.forename: Radha S
authors.initials: RS
authors.lastname: Chari
authors.affiliation: Department of Medicine, University of Colorado Denver School of Medicine, Denver, Colorado; and.
authors.forename: Colleen G
authors.initials: CG
authors.lastname: Julian
authors.affiliation: Division of Pulmonary Medicine, Faculty of Medicine, University of Alberta, Edmonton, Canada.
authors.forename: Michael K
authors.initials: MK
authors.lastname: Stickland
authors.affiliation: Program for Pregnancy and Postpartum Health, Physical Activity and Diabetes Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Canada; Alberta Diabetes Institute, Women and Children's Health Research Institute, and.
authors.forename: Margie H
authors.initials: MH
authors.lastname: Davenport
authors.affiliation: Program for Pregnancy and Postpartum Health, Physical Activity and Diabetes Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Canada; Alberta Diabetes Institute, Women and Children's Health Research Institute, and craig.steinback@ualberta.ca.
authors.forename: Craig D
authors.initials: CD
authors.lastname: Steinback
mesh_terms: D000328:Adult; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D003971:Diastole / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D018482:Muscle, Skeletal / Q000502:physiology; D011247:Pregnancy; D012146:Rest / Q000502:physiology; D013564:Sympathetic Nervous System / Q000502:physiology*; D014630:Vagus Nerve / Q000502:physiology
keywords: baroreflex control; blood pressure; pregnancy; sympathetic nerve activity