Effects of Gender on Heart Rate Variability at Rest and During Upright Tilt

Abstract

1462 Heart Rate Variability (HRV) differs between men and women at rest, with women exhibiting higher parasympathetic tone. Baroreceptor sensitivity is lower in women, but it is unknown if HRV in response to an orthostatic challenge differs between men and women. PURPOSE: To investigate potential gender differences in HRV during upright tilt in men and women matched for VO2 max. METHODS: 7 males (age = 21.7 ± .64 yrs., ht = 169.9 ± 6.5cm, wt = 83.4 ± 7.9kg), and 7 females (age = 20.5 ± .57 yrs., ht = 156.4 ± 7.5cm, wt = 68.1 ± 4.3kg) completed a maximal exercise test, and on a different day, 10 minutes of supine rest, 10 minutes upright tilt (80 degrees), and 10 minutes of supine recovery with continuous ECG measurements. A metronome was used to pace breathing at 12 breaths-per-minute. An autoregressive approach was used to evaluate HRV in the frequency domain [total power (TP), low frequency (LF), high frequency (HF)]. Data were analyzed using an ANOVA with repeated measures. RESULTS: TP was greater in females at rest (13728.7 ± 2497.4 > 5338.4 ± 2497.4), tilt (6207.0 ± 1694.5 > 4783.8 ± 1694.5), and recovery (12757.7 ± 1833.4 > 4528.7 ± 1833.4). Similar results were also shown for absolute HF power. However, normalized LF, HF, and LF: HF showed no significant gender differences for any condition (p>0.05). CONCLUSIONS: These results show that TP and absolute HF power was higher in women at rest and during upright tilt, suggesting greater parasympathetic tone in women, consistent with previous data. However, normalized LF and HF power was not different between genders, suggesting that autonomic control of HR at rest and during upright tilt is similar for both men and women.