Sympathetic Action Potential Firing and Recruitment Patterns Are Abnormal in Gestational Hypertension

Abstract

Background: We tested the hypothesis that women who develop gestational hypertension (GH) display abnormal sympathetic action potential (AP) discharge patterns during late pregnancy (32–36 weeks), both at supine rest and during postural stress. Methods: Thirteen nonpregnant, female controls (nonpregnant controls [CTRL]) and 32 pregnant women participated; 14 had low-risk (no personal history of GH) normal pregnancies (LR-NP), 10 had high-risk (personal history of GH) normal pregnancies (HR-NP), and 8 developed GH. We measured heart rate, blood pressure, and muscle sympathetic nerve activity (microneurography) at supine rest and 60° head-up tilt. Sympathetic AP patterns were studied using wavelet-based methodology. Results: At rest, muscle sympathetic nerve activity burst frequency was elevated in LR-NP, HR-NP, and GH versus CTRL (all P ≤0.01); however, the AP content per integrated burst was augmented only in GH (20±5 spikes/burst), compared with CTRL (8±3 spikes/burst), LR-NP (9±2 spikes/burst) and HR-NP (11±4 spikes/burst; all P <0.0001). Thus, total AP firing frequency was greater in GH versus each of CTRL, LR-NP, and HR-NP (all P <0.0001). In pregnancy, AP frequency is related directly to systolic (R 2 =46%) and diastolic (R 2 =20%) blood pressure (both P ≤0.01). Unlike CTRL (both P <0.01), women who developed GH were unable to increase within-burst AP firing ( P =0.71) or recruit latent subpopulations of larger-sized APs ( P =0.72) in response to head-up tilt, perhaps related to a ceiling-effect; however, total AP firing frequency in the upright posture was elevated in the GH cohort versus CTRL, LR-NP, and HR-NP (all P <0.05). Conclusions: Women who develop GH display aberrant sympathetic AP firing patterns in both the supine and upright postures.