Influence of sex, menstrual cycle and oral contraceptives on cerebrovascular resistance and cardiorespiratory function during Valsalva or standing

Women experience orthostatic intolerance more than men, and experience faintness more in the early follicular (i.e. low hormone (LH)) compared to the luteal (i.e. high hormone (HH)) phase of the menstrual cycle. Men (n=13, age: 25.8±1.8) and women in the LH (day 2-5; placebo) and HH) (day 18-24; high dose) phases of the menstrual cycle with (OC; n=14, age: 22.0±0.8) or without oral contraceptives (NOC; n=12, age: 21.8±0.5) underwent the Valsalva maneuver and a supine-sit-stand protocol. Blood pressure, normalized stroke volume (SVi), cardiac output index (Qi), heart rate (HR), end-tidal carbon dioxide (ET-CO₂), and middle cerebral artery blood velocity (MCA) were measured. Valsalva: All women had a greater increase in diastolic and mean MCA compared to men (p≤0.065) with no significant effect of menstrual cycle or OC use. Supine-sit-stand: Sex: Men had lower MCA (p<0.038) than all women, and higher SVi compared to NOC in all postures (p<0.011) and OC-LH during stand (p=0.010). Only men experienced higher resistance index (RI; p<0.001) and pulsatility index (PI; p<0.001) with standing. OC: OC had lower ET-CO₂ (p=0.002) compared to NOC (p=0.030) and men (p≤0.067). Compared to NOC, OC had higher SVi (p=0.004) and Qi (p=0.008). Phase: HH tended to have lower mean MCA (p=0.058) and higher SVi (p=0.059) and PI (p=0.058) than LH. OC x Phase: OC users had higher MAP than NOC in LH (p=0.049) and lower MAP in HH compared to themselves in LH (p=0.014). Our results indicate that cycling estrogens/progestins can influence ventilatory, cardiovascular and/or cerebrovascular physiology.

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