Effects of menstrual cycle on cardiac autonomic innervation as assessed by heart rate variability

The aim of the study was to investigate the effects of menstrual cycle on cardiac autonomic function parameters in young healthy women by means of heart rate variability (HRV).

Forty-three nonobese regularly cycling women (age 29 +/- 6, range 20-38) were enrolled. Recordings for HRV analysis were obtained during the two phases of the menstrual cycle when the estrogen and progesterone levels peaked (follicular phase 11 +/- 1 days and luteal phase 21 +/- 1 days from the start of bleeding). Power spectral analysis of HRV was performed to calculate the low frequency peak (LF, 0.04-0.15 Hz), high frequency peak (HF, 0.15-0.40 Hz), LF in normalized unit (LF nU), HF in normalized unit (HF nU), and LF/HF ratio during the two phases of menstrual cycle.

The heart rates, LF and HF, were similar in both phases (P > 0.05). A significant increase was noted in the LF NU in the luteal phase compared to follicular phase of the menstrual cycle (P = 0.014), whereas a tendency for increased HF NU was observed in the follicular phase (P = 0.053). Furthermore, LF/HF ratio was significantly higher in the luteal phase compared to follicular phase (2.1 +/- 1.5 vs 1.6 +/- 0.9, P = 0.002), suggesting increased sympathetic activity in the luteal phase.

We concluded that regulation of autonomic tone is modified during menstrual cycle. The alteration in the balance of ovarian hormones might be responsible for these changes in the cardiac autonomic innervation.