Abstract
Plasma volume (PV) varies with the menstrual cycle not only in healthy parous controls (CON) but also in formerly preeclamptic women with a subnormal PV (LPV). It is unknown whether formerly preeclamptic women with LPV are more susceptible to orthostatic stress than healthy controls. In this study, the authors compared autonomic responses to acute (standing from supine position) and gradual (menstrual cycle) orthostatic stress between LPV and CON. In 11 LPV (PV[.lessequal] 49 mL/kg lean body mass) and 7 CON, beat-to-beat blood pressure (BP) and heart rate (HR) were measured in supine position and after an orthostatic stress test, during the follicular phase (FP) and luteal phase (LP) of the menstrual cycle. Spectral analysis (fast Fourier transform) was performed on beat-to-beat signals to quantify the magnitude of the spontaneous BP and pulse interval (PI) fluctuations. The absolute powers within the low-frequency (0.04-0.15 Hz) and high-frequency (0.15-0.4 Hz) ranges of BP and PI were used as estimates for sympathetic and parasympathetic activity, respectively. Baroreflex sensitivity was calculated as the transfer function gain from low-frequency systolic BP to PI. Differences between groups, menstrual phase, and response to standing were compared by analysis of variance. Basal BP was comparable in both study groups. However, basal PI and spontaneous baroreflex sensitivity were lower in LPV than in CON. The autonomic responses to acute and gradual orthostatic stress were similar in the 2 groups, irrespective of the phase of the menstrual cycle. The cardiovascular response to acute and gradual orthostatic stress in both FP and LP is comparable in LPV and CON.