Heart rate variability under resting conditions in postmenopausal and young women

The aim of the present study was to compare the modulation of heart rate in a group of postmenopausal women to that of a group of young women under re sting conditions on the basis of R-R interval variability. Ten healthy post menopausal women (mean +/- SD, 58.3 +/- 6.8 years) and 10 healthy young wom en (mean +/- SD, 21.6 +/- 0.82 years) were submitted to a control resting e lectrocardiogram (ECG) in the supine and sitting positions over a period of 6 min. The ECG was obtained from a one-channel heart monitor at the CM5 le ad and processed and stored using an analog to digital converter connected to a microcomputer. R-R intervals were calculated on a beat-to-beat basis f rom the ECG recording in real time using a signal-processing software. Hear t rate variability (HRV) was expressed as standard deviation (RMSM) and mea n square root (RMSSD). In the supine position. the postmenopausal group sho wed significantly lower (P <0.05) median values of RMSM (34.9) and RMSSD (2 2.32) than the young group (RMSM: 62.11 and RMSSD: 49.1). The same occurred in the sitting position (RMSM: 33.0 and RMSSD: 18.9 compared to RMSM: 57.6 and RMSSD: 42.8 for the young group). These results indicate a decrease in parasympathetic modulation in postmenopausal women compared to young women which was possibly due both to the influence of age and hormonal factors. Thus, time domain HRV proved to be a noninvasive and sensitive method for t he identification of changes in autonomic modulation of the sinus node in p ostmenopausal women.