Heart rate variability across the menstrual cycle in young women taking oral contraceptives.

Previous studies have shown that resting heart rate variability (HRV) is modified by different phases of the menstrual cycle in nonusers of oral contraceptive pills (OCP); however, the effect of OCP on autonomic control of the heart remains unclear. The purpose of this study was to investigate HRV during the low hormone (LH-not taking OCP) and during the high hormone (HH-active OCP use) phases of the menstrual cycle in young women. Seventeen healthy women (19-31 years) taking OCP for at least 6 consecutive months were enrolled in this study. Plasma estradiol and progesterone were verified at each visit. HRV was assessed by using one-lead electrocardiography in time and frequency domains, in which participants rested in the supine position for a 20-min period with a breathing rate of 15 cycles/min. In addition, resting heart rate, and systolic and diastolic blood pressure were obtained. Both plasma estradiol (LH: 19.8 ± 4.2 pg/mL vs. HH: 12.4 ± 1.5 pg/mL; p > .05) and progesterone (LH: 0.247 ± 0.58 ng/mL vs. HH: 0.371 ± 0.08 ng/mL; p > .05) (mean ± SE) levels were similar in both phases. No significant difference was obtained for any component of HRV, heart rate, or blood pressure between the LH and HH phases (p > .05). These results provide preliminary evidence that use of OCP does not affect HRV during the menstrual cycle in healthy women.