Changes of respiratory sinus arrhythmia during the menstrual cycle depend on average heart rate.

To evaluate the complex time course of changes in respiratory sinus arrhythmia (RSA) during the menstrual cycle, daily beat-to-beat morning recordings of heart rate (HR) were carried out in 26 healthy female subjects (age 20-29 years) during two menstrual cycles. For determination of fast, vagally mediated variations of HR we used a robust time-domain measure of RSA (logRSA). We found pronounced changes in HR during the menstrual cycle with a minimum in the early follicular phase and a maximum in the late luteal phase. There were large differences between individuals in the fluctuations of logRSA during the menstrual cycle that were related to average HR: subjects with a low HR exhibited higher values of logRSA in the luteal compared to the follicular phase, whereas the trend was reversed in subjects with a high HR. The difference of extreme points of logRSA fluctuations (early follicular and mid luteal phase) was correlated to average HR (r=-0.64, P < 0.001). We conclude that different patterns of RSA fluctuations occur depending on the level of average HR.