Circadian pattern of heart rate variability in chronic heart failure patients. Effects of physical training

The effect of physical training on the circadian pattern of heart rate variability (recorded over 24 h in relation to both time and frequency) was assessed in 12 chronic heart failure patients randomized, in a cross-over design, to 8 weeks training or detraining, and compared with 12 age-matched normals. Training improved heart rate variability indices: all R-R interval 5 min standard deviations increased by 17.6%, the root mean square of the differences of successive R-R intervals by 34.9%, the percentage difference between adjacent normal R-R intervals > 50 ms by 112.5%, total power by 58.3%, high frequency by 128.5% and low frequency by 65.0%. Compared with controls, circadian variations in autonomic parameters were maintained in chronic heart failure. Training-induced changes were observed at different time intervals throughout the day: the highest values were at 0100 h-0700 h (detraining: low frequency 361 +/- 83 ms2, high frequency 126 +/- 47 ms2; training: low frequency 535 +/- 202 ms2, high frequency 227 +/- 115 ms2, P < 0.01) and the lowest at 1300 h-1900 h (detraining: low frequency 91 +/- 23 ms2, high frequency 39 +/- 14 ms2; training: low frequency 154 +/- 42 ms2, high frequency 133 +/- 67 ms2, P < 0.05). In chronic heart failure, training maintains and improves circadian variations in heart rate variability measures.