Abstract
A time- or frequency-domain analysis of RR interval variability has been generally used as an indirect estimate of cardiac autonomic activity to the sinoatrial node of the heart. The basic assumption for this analysis is that the variability of RR interval would be always coincident with the variability of PP interval. However, we have recently found that the variability of RR interval becomes much smaller during dynamic exercise than that of PP interval, despite the same shortened average interval. Thus, we hypothesized that a high frequency component (HF at 0.15-0.40 Hz) of PP interval variability, not RR interval variability, was a better estimate of cardiac vagal outflow. To test this hypothesis, the HF components of the power spectrums of PP and RR interval variability during dynamic exercise were assessed using a Wavelet transform. Nine athletes and six sedentary subjects performed ergometer exercise to increase heart rate (HR) to 160 beats/min from the baseline. During resting, HF of RR interval variability was coincident with that of PP interval variability. In contrast, although HF of RR interval variability decreased to nearly zero at 160 beats/min during exercise, HF of PP interval was considerably present. We conclude that cardiac vagal outflow to the sinoatrial node is better estimated by HF of PP interval variability. The conclusion leads to an idea that substantial cardiac parasympathetic activity exists at a higher HR during dynamic exercise. [J Physiol Sci. 2008;58 Suppl:S179]
