The effect of oestrogen on cerebrovascular regulation in eumenorrheic women : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science, Massey University, Wellington, New Zealand
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2020
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Massey University
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Abstract
Women experience fluctuating sex hormone concentrations throughout their lifetime and while their role in reproduction is well documented, there is little knowledge of the effects of the changing hormone concentrations on women’s cerebrovascular health. Therefore, this study examined dynamic cerebral autoregulation (dCA) in 10 healthy eumenorrheic women (28 ± 7 years) volunteers. The participants dCA was examined at three different phases of the menstrual cycle: early follicular (EF; when oestrogen and progesterone concentrations are low), late follicular (LF; oestrogen concentrations are high, while progesterone remains steady), and mid-luteal (ML; oestrogen and progesterone concentrations are high). The dCA was assessed using the autoregulatory index (AI) of forced changes in blood pressure (BP) and mean middle cerebral blood velocity (MCAv) response, induced during phases of the Valsalva manoeuvre (VM). The VM is a four-phase manoeuvre that produces hyper- and hypotensive changes to blood pressure (BP): phase I (initial increase in BP), phase IIa (initial decrease in BP), phase IIb (stabilisation of BP), phase III (decrease in BP after cessation of breath-hold), and phase IV (overshoot in BP recovery). Resting mean arterial blood pressure (MAP, P= 0.409), MCAv (P= 0.635), and cerebrovascular conductance index (CVCi, P= 0.984) were not different throughout all trials. The partial pressure of endtidal carbon dioxide (PETCO₂) was unchanged between the trials (P = 0.907). The VM induced middle cerebral artery velocity mean (MCAvmean) differences between trials (interaction: P = 0.039), MCAv during mid-luteal (ML; 58 ± 15 cm/s) showed a significant difference to early follicular (EF; 51 ± 14 cm/s, P = 0.013) and late follicular (LF; 49 ± 15 cm/s, P = 0.024) during phase IIb of the VM. There were no differences in MAP (P = 0.233) and CVCi (P = 0.808) during the VM throughout the trials. AI presented no difference during phase II of the VM (P= 0.354), however, phase IV did show a trend (P= 0.086). The results of this study indicate that circulating ovarian hormone concentrations may regulate responses to dynamic cerebrovascular challenges.
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Figures 1 (=Vselja et al., 2014 Fig 1) and 2 (=Ainslie & Duffin, 2009 Fig 2) were removed for copyright reasons. Figure 6 remains for the sake of clarity.