RESPIRATORY VARIABILITY IN R-R INTERVAL DURING SINUSOIDAL EXERCISE

The R-R interval varies with the cycles of respiration. The response o f the variability in the R-R interval with respiration was examined du ring sinusoidal cycle exercise in 12 healthy young male subjects. Work rate varied sinusoidally between 30 W and 60% maximal oxygen uptake f or an 8-min period. The higher the heart rate (HR), the smaller was th e magnitude of the variation in R-R interval with respiration (Delta R R). When HR increased with an increase in exercise intensity, however, Delta RR tended to decrease more markedly at lower HR. On the other h and, since Delta RR generally increased linearly during the decrease i n KR with a reduction in exercise intensity, Delta RR was greater duri ng decreases in HR than during increases in HR at a similar HR. These results suggest that the contribution of the withdrawal of cardiac par asympathetic activity to increases in HR with increases in exercise in tensity during sinusoidal exercise were greater at lower HR, and that the cardiac parasympathetic system was more activated during HR decrea ses than during HR increases at the same HR. From our findings it woul d seem that such complex parasympathetic HR regulaltion during sinusoi dal exercise, which depends on the level of HR and the direction of th e change in HR, may be influenced by factors other than the parasympat hetic system, such as the cardiac sympathetic system.