Phase of the menstrual cycle does not affect orthostatic tolerance in healthy women

Women of child-bearing age have a lower orthostatic tolerance (OT) than older women or men, and women suffering from frequent syncopal episodes often comment that their symptoms occur at certain times of the menstrual cycle. However, it is not known whether, in asymptomatic women, OT varies at different phases of the menstrual cycle. We studied 8 healthy asymptomatic women aged 26.8±3.4 years. We determined OT using a test of combined head-up tilting and lower body suction. We continuously monitored beat-to-beat blood pressure (Finapres), heart rate (ECG), and cerebral and forearm blood flow velocities (Doppler ultrasound). On each test day we assessed carotid baroreceptor sensitivity from suction/pressure applied to a neck chamber. We also determined estradiol and progesterone levels from a venous blood sample. Tests were performed in early follicular and late luteal phases, and during ovulation. Serum concentrations of estradiol (pmol • l–1) and progesterone (nmol • l–1) were in follicular phase 464.1 ± 63 and 6.3 ± 2.8; ovulation 941.6 ± 298 and 5.8 ± 1.2; luteal phase 698±188 and 32.3 ± 9.6. Progesterone levels were significantly higher in the luteal phase (p < 0.001). OT was not different on any test day: follicular 31.9 ± 1.6 min, ovulation 31.3 ± 0.7 min; luteal 31.1 ± 2.2 min. Supine and tilted heart rates and blood pressures, the maximum heart rate, and the cerebral autoregulatory and forearm vascular resistance responses to the orthostatic stress were similar during all studies. Both cardiac and vascular resistance carotid baroreceptor sensitivities were also similar on all test days. These results suggest that there is no difference in either OT or cardiovascular control at the tested phases of the menstrual cycle in healthy women.