Does the menstrual cycle influence the sensitivity of vagally mediated baroreflexes?
The menstrual cycle provokes several physiological changes that could influence autonomic regulatory mechanisms. We studied the carotid-cardiac baroreflex in ten healthy young women on four occasions over the course of their menstrual cycles (days 0-8, 9-14, 15-20 and 21-25). We drew blood during each session for analysis of oestrogen, progesterone and noradrenaline (norepinephrine) levels, and assessed carotid-cardiac baroreflex function by analysing R-R interval responses to graded neck pressure sequences. Oestrogen levels followed a classical two-peak (cubic) response, with elevated levels on days 9-14 and 21-25 compared with days 0-8 and 15-20 (P =0.0032), while progesterone levels increased exponentially from days 9-14 to days 21-25 (P = 0.0063). Noradrenaline levels increased from an average of 137pg/ml during the first three measurement periods to 199pg/ml during days 21-25 (P = 0.0456). Carotid-cardiac baroreflex gain and operational point were not statistically different at any of the time points during the menstrual cycle (P⩾0.18). These findings are consistent with the notion that beat-to-beat vagal-cardiac regulation does not change over the course of the normal menstrual cycle.
Cooke, W. H.,
Ludwig, D. A.,
Hogg, P. S.,
Eckberg, D. L.,
Convertino, V. A.
Does the menstrual cycle influence the sensitivity of vagally mediated baroreflexes?.
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