Sex Differences in Cerebral Autoregulation is Unaffected by Menstrual Cycle Phase in Young, Healthy Women.

Sex is known to affect the prevalence of conditions such as stroke. However, effects of sex on cerebral blood flow regulation are still not well understood. Critical to this understanding is how fluctuations in hormones across the menstrual cycle affect cerebral autoregulation. We measured autoregulation in early follicular, late follicular, and mid-luteal phases during spontaneous and induced blood pressure oscillations in 26 (13 women) young (26 ± 4 years), healthy individuals. Men participated 3 times, ~1-3 weeks apart. Beat-by-beat blood pressure, heart rate, end-tidal CO2 , and transcranial Doppler ultrasonography of the middle (MCA) and anterior (ACA) cerebral arteries were obtained. We did not find a difference in cerebral autoregulation across the menstrual cycle in women, but found significantly improved autoregulation in the MCA and ACA of women compared to men. Women demonstrated significantly lower MCA gain (0.97 ± 0.13 vs 1.17 ± 0.14 %/mmHg; p=0.001), higher MCA phase (46.1 ± 12.6 vs 35.8 ± 7.9°; p=0.019), and higher ACA phase (31.5 ± 8.5 vs 40.5 ± 10.8°; p=0.040) during repeated squat-to-stand maneuvers. Women also had lower MCA gain (1.50 ± 0.11 vs 1.72 ± 0.30 %/mmHg; p=0.029) during spontaneous fluctuations in pressure while standing, and less of a decrease in MCA flow velocity (-23.2 ± 6.0 vs -18.7 ± 2.7 %; p= 0.014) during sit-to-stand maneuvers. Our results suggest that young women have improved cerebral autoregulation compared to young men regardless of menstrual cycle phase and that autoregulation is relatively robust to acute fluctuations in female sex hormones.