Influence of respiratory cycle on heart rate variations

In 46 normal subjects, we examined a) the component of respiratory sinus arrhythmia (-HF), b) the component coefficient of variance of HF (CCV-HF), c) the component of Mayer wave related sinus arrhythmia (=LF), and d) LF/HF ratio. Both of a) and b) are thought to reflect parasympathetic activity, and both of c) and d) are thought to reflect sympathetic activity. We studied how the heart rate variations are influenced by respiratory cycle (CY). At first, we performed the regression analysis between the heart rate variations and CY as an intrasubject factor using all subjects' data. The square of partial correlation of each dependent variable and log CY was; for log HF R²=0.7334 (F(1,191)=526.25, p<0.0001), for log CCV-HF R²=0.7307 (F(1,190)=515.57, p<0.0001), for log MWSA R²=0.4568 (F(1,191)=106.37, p<0.0001), and for log (LF/HF) R²=0.6703 (F(1, 191)=388.34, p<0.0001). Then we predicted the heart rate variations employing CY as the parameter, and examined the reliability by cross validation. For instance, Pearson correlation between the real value of LF/HF (CY= 15) and the value predicted from the real value of LF/HF (CY=20) for each subject was 0.9866 (p<0.0001). With this study, we concluded that the heart rate variations could be assessed more accurately, considering the influence of respiratory cycle. The heart rate variations modified by respiratory cycle would be used clinically as a reliable index of autonomic nervous function in the future.