Cerebral autoregulation across the menstrual cycle in eumenorrheic women

Abstract

There is emerging evidence that ovarian hormones play a significant role in the lower stroke incidence observed in pre-menopausal women compared with men. However, the role of ovarian hormones in cerebrovascular regulation remains to be elucidated. We examined the blood pressure-cerebral blood flow relationship (cerebral autoregulation) across the menstrual cycle in eumenorrheic women (n = 12; mean ± SD: age, 31 ± 7 years). Participants completed sit-to-stand and Valsalva maneuvers (VM, mouth pressure of 40 mmHg for 15 s) during the early follicular (EF), late follicular (LF), and mid-luteal (ML) menstrual cycle phases, confirmed by serum measurement of progesterone and 17β-estradiol. Middle cerebral artery blood velocity (MCAv), arterial blood pressure and partial pressure of end-tidal carbon dioxide were measured. Cerebral autoregulation was assessed by transfer function analysis during spontaneous blood pressure oscillations, rate of regulation (RoR) during sit-to-stand maneuvers, and Tieck's autoregulatory index during VM phases II and IV (AI-II and AI-IV, respectively). Resting mean MCAv (MCAv_mean ), blood pressure, and cerebral autoregulation were unchanged across the menstrual cycle (all p > 0.12). RoR tended to be different (EF, 0.25 ± 0.06; LF; 0.19 ± 0.04; ML, 0.18 ± 0.12 sec^-1 ; p = 0.07) and demonstrated a negative relationship with 17β-estradiol (R² = 0.26, p = 0.02). No changes in AI-II (EF, 1.95 ± 1.20; LF, 1.67 ± 0.77 and ML, 1.20 ± 0.55) or AI-IV (EF, 1.35 ± 0.21; LF, 1.27 ± 0.26 and ML, 1.20 ± 0.2) were observed (p = 0.25 and 0.37, respectively). Although, a significant interaction effect (p = 0.02) was observed for the VM MCAv_mean response. These data indicate that the menstrual cycle has limited impact on cerebrovascular autoregulation, but individual differences should be considered.

Keywords: cerebral autoregulation; eumenorrheic women; menstrual cycle.

FIGURE 1

Experimental Protocol. ECG, Electrocardiogram; TCD, transcranial Doppler; MCAv, middle cerebral artery blood velocity; ABP, arterial blood pressure; P_ETCO₂, Partial pressure of end‐tidal carbon dioxide

FIGURE 2

Relationship between resting cerebrovascular conductance index (CVCi), pulsatility index (Pi), mean middle cerebral artery blood velocity (MCAv_mean), the average rate of regulation (RoR) as calculated following sit‐to‐stand maneuvers, and Tieck’s autoregulatory index (Tiecks, Lam, Matta, et al., 1995) during phase II (AI – II) and phase IV (AI‐IV) of the Valsalva maneuver, and 17β‐estradiol during EF and LF phases only (n = 12 for all, 12 × EF and 10 × LF trials)

FIGURE 3

Typical trace for a 40 mm Hg Valsalva maneuver. MCAv, middle cerebral artery blood velocity; MAP, mean arterial blood pressure; HR, heart rate, and mouth pressure as a surrogate for intrathoracic pressure; PI, Valsalva maneuver phase I; PIIa, phase IIa; PIIb, phase IIb; PIII, phase III; PIV, phase IV. Thick black line represents the mean value for each cardiac cycle within the MAP and MCAv trace

FIGURE 4

Valsalva maneuver hemodynamics across the menstrual cycle. MAP, mean arterial blood pressure; MCAv_mean, mean middle cerebral artery blood velocity; CVCi, cerebrovascular conductance index; Pi, pulsatility index; PP, pulse pressure; PI, Valsalva maneuver phase I; PIIa, phase IIa; PIIb, phase IIb; PIII, phase III; PIV, phase IV. *, significant difference between late follicular and mid‐luteal within Valsalva maneuver phase (p = 0.02) and trend for the difference between late follicular and early follicular (p = 0.06); †, significant difference between early follicular and mid‐luteal within Valsalva maneuver phase (p = 0.03). Data are means ± SD