PHYSICAL ACTIVITY STATUS DOES NOT AFFECT AGE-RELATED CHANGES IN HEART RATE VARIABILITY IN WOMEN 848:

Low heart rate variability (HRV) is associated with an increased risk of cardiac sudden death, coronary heart disease, and all-cause mortality. We have previously shown that physically active (PA) postmenopausal (POST) women demonstrate higher levels of HRV and spontaneous cardiac baroreflex sensitivity (SBRS) compared to their healthy sedentary (S) peers (Davy et al.Am J Physiol. 271: H455-H460, 1996). The purpose of the present study was to test the hypothesis that HRV and SBRS would be reduced with age in healthy S but not PA women. To accomplish this, we measured HRV (both time and frequency domain) and SBRS in the sitting posture in 23 healthy S women: 11 premenopausal (PRE) S and 12 POST-S (age= 28±1 and 61±2 yr, VO2max= 35.3±1.4 and 21.7±1.5 ml/kg/min, respectively) and in 23 PA women: 12 PA women: 12 Pre-PA and 11 POST-PA (age= 31±1 and 59±2 yr, VO2max= 52.5±1.4 and 39.7±1.8 and ml/kg/min). The standard deviation of the R-R interval (time domain) was reduced (P<0.05) with age in both S (52±6 vs. 33±4 ms) and PA(72±8 vs. 49±9 ms). The high frequency power (3740±1527 vs. 915±188 and 9516±2849 vs. 2803±1083 ms2/mmHg), and total power of HRV, and SBRS (11±2 vs. 7±2 and 19±3 vs. 13±2 ms/mmHg) also demonstrated similar age-related reductions in S and PA women, respectively (all P<0.05). SBRS accounted for 60% of the variance in the high frequency power of HRV. Therefore, in contrast to our hypothesis, the results of the present study suggest that HRV and SBRS decline similarly with age in healthy S and PA women. However, PA women demonstrate higher levels of HRV and SBRS compared to their S peers, regardless of age.