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

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 degrees 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.