No Effect of Menstrual Phase on Cardiovascular Hemodynamic or Autonomic Responses to Orthostatic Stress

Abstract

1460 Estrogens are powerful vasodilators, and changes in estrogen concentrations across the menstrual cycle could affect regional fluid pooling and compensatory autonomic responses to an orthostatic challenge. PURPOSE: To compare cardiovascular hemodynamic and autonomic responses in women during low- and high-estrogen phases of the menstrual cycle during graded, progressive lower body negative pressure (LBNP). METHODS: Eight young (age 21.8 ± 2.2 yr) eumenorrheic women were studied twice, once during low-estrogen (0–5 day) and once during high-estrogen (20–25 day) phases of the menstrual cycle. Plasma estradiol levels were measured, and then subjects were instrumented with a 3-lead ECG, pneumobelt for respiratory excursions, finger photoplethysmograph for beat-by-beat blood pressure, and segmental bioimpedance for estimation of fluid shifts (thorax, pelvis, and leg). Subjects were placed in an air-tight chamber at the level of the iliac crest. Data were collected during 5 min of controlled frequency breathing (0.25 Hz) at 0, −10, −20, −30, −40 and −50 mmHg chamber decompression and analyzed in both time and frequency domains. RESULTS: Estradiol concentrations were 48 ± 6 and 147 ± 26 pg/ml during days 0–5 and 20–25 (p<0.05). R-R interval and R-R interval spectral power, stroke volume and cardiac output, and systolic pressure to R-R interval transfer function magnitude decreased progressively during LBNP (p<0.05). Mean arterial pressure was maintained with increases of peripheral resistance. Segmental fluid shifts and cardiovascular responses to LBNP were not different during high- and low-estrogen phases. CONCLUSION: Despite increased potential for vascular dilation with high plasma estradiol concentrations, our results demonstrate normal cardiovascular hemodynamic and autonomic compensatory responses in young eumenorrheic women to simulated orthostatic stress during different menstrual phases. Supported by NIH Grant R15 HL67787-01