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 ms²), but the HF index increased (6.7±0.7 vs. 7.1±0.7 ms², 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.