Respiratory variability in R-R interval during sinusoidal exercise.

Abstract

The R-R interval varies with the cycles of respiration. The response of the variability in the R-R interval with respiration was examined during sinusoidal cycle exercise in 12 healthy young male subjects. Work rate varied sinusoidally between 30 W and 60% maximal oxygen uptake for an 8-min period. The higher the heart rate (HR), the smaller was the magnitude of the variation in R-R interval with respiration (delta RR). When HR increased with an increase in exercise intensity, however, delta RR tended to decrease more markedly at lower HR. On the other hand, since delta RR generally increased linearly during the decrease in HR with a reduction in exercise intensity, delta RR was greater during decreases in HR than during increases in HR at a similar HR. These results suggest that the contribution of the withdrawal of cardiac parasympathetic activity to increases in HR with increases in exercise intensity during sinusoidal exercise were greater at lower HR, and that the cardiac parasympathetic system was more activated during HR decreases than during HR increases at the same HR. From our findings it would seem that such complex parasympathetic HR regulaltion during sinusoidal exercise, which depends on the level of HR and the direction of the change in HR, may be influenced by factors other than the parasympathetic system, such as the cardiac sympathetic system.