DYNAMIC HEART-RATE-VARIABILITY - A TOOL FOR EXPLORING SYMPATHOVAGAL BALANCE CONTINUOUSLY DURING SLEEP IN MEN

We have recently demonstrated that the overnight profiles of cardiac i nterbeat autocorrelation coefficient of R-R intervals (r(RR)) calculat ed at 1-min intervals are related to the changes in sleep electroencep halographic (EEG) mean frequency, which reflect depth of sleep. Other quantitative measures of the Poincare plots, i.e., the standard deviat ion of normal R-R intervals (SDNN) and the root mean square difference among successive R-R normal intervals (RMSSD), are commonly used to e valuate heart rate variability. The present study was designed to comp are the nocturnal profiles of r(RR), SDNN, and RMSSD with the R-R spec tral power components: high-frequency (HF) power, reflecting parasympa thetic activity; low-frequency (LF) power, reflecting a predominance o f sympathetic activity with a parasympathetic component; and the LF-to -HF ratio (LF/HF), regarded as an index of sympathovagal balance. r(RR ), SDNN, RMSSD, and the spectral power components were calculated ever y 5 min during sleep in 15 healthy subjects. The overnight profiles of r(RR) and LF/HF showed coordinate variations with highly significant correlation coefficients (P < 0.001 in all subjects). SDNN correlated with LF power (P < 0.001), and RMSSD correlated with HF power (P < 0.0 01). The overnight profiles of r(RR) and EEG mean frequency were found to be closely related with highly cross-correlated coefficients (P < 0.001). SDNN and EEG mean frequency were also highly cross correlated (P < 0.001 in all subjects but 1). No systematic relationship was foun d between RMSSD and EEG mean frequency. In conclusion, r(RR) appears t o be a new tool for evaluating the dynamic beat-to-beat interval behav ior and the sympathovagal balance continuously during sleep. This nonl inear method may provide new insight into autonomic disorders.