Cardiac vagal outflow after aerobic training by analysis of high-frequency oscillation of the R-R interval.

This study was designed to assess the effect of aerobic training on the dynamics between the R-R interval length and the high-frequency (HF) oscillation of the R-R interval. Seventeen healthy males (26+/-2 years) participated in an 8-week aerobic training intervention. The mean HF spectral power (0.15-0.4 Hz) of the R-R interval and the mean R-R interval length were analyzed from 24-h recordings. HF power was also analyzed in 5-min sequences and plotted as a function of the corresponding mean R-R interval length. The relationship between the R-R interval length and the HF power was analyzed by a quadratic regression model. The relationship was defined as saturated if the distinct deflection point of the model occurred before the maximum R-R interval. Otherwise, the relationship was defined as linear. Additionally, the mean HF power was calculated from the linear portion of the R-R interval versus the HF power regression curve (HF index). Before the training intervention, seven subjects had a saturated HF power. After the intervention, five new cases of saturated HF power were observed. The mean HF power of the 24-h recording did not change in the group with a saturated HF power before training (7.4+/-0.8 vs. 7.6+/-0.8 ms(2)), but the HF index increased (6.7+/-0.7 vs. 7.1+/-0.7 ms(2), P<0.05). We conclude that enhanced vagal activity due to aerobic training increases the prevalence of the saturation of the HF oscillation of the R-R interval variability in healthy subjects. HF power calculated from unsaturated area detects more accurately subtle changes in the vagally mediated beat-to-beat variability of the R-R interval after aerobic training than the mean 24-h HF power.