DYNAMICS OF SPECTRAL COMPONENTS OF HEART-RATE-VARIABILITY DURING CHANGES IN AUTONOMIC BALANCE

Frequency domain analysis of heart rate variability (HRV) has been pro posed as a semiquantitative method for assessing activities in the aut onomic nervous system. We examined whether absolute powers, normalized powers, and the low frequency-to-high frequency ratio (LF/HF) derived from the HRV power spectrum could detect shifts in autonomic balance in a setting with low sympathetic nervous tone. Healthy subjects were examined for 3 h in the supine position during 1) control conditions ( n = 12), 2) acute beta-blockade (n = 11), and 3) chronic beta-blockade (n = 10). Heart rate fell during the first 40 min of the control sess ion (72 +/- 2 to 64 +/- 2 beats/min; P < 0.005) and was even lower dur ing acute and chronic P-blockade (56 +/- 2 beats/min; P < 0.005). The powers of all spectral areas rose during the first 60 min in all three settings, more so with beta-blockade (P < 0.05). LF/HF was found to c ontain the same information as powers expressed in normalized units. L F/HF detected the shift in autonomic balance induced by beta-blockade but not the change induced by supine position. In conclusion, none of the investigated measures derived from power spectral analysis compreh ensively and consistently described the changes in autonomic balance.