Individual features of circulatory power spectra in man

Rhythms of resting fluctuations of circulatory parameters in man reveal a considerable interindividual variability. We posed the question whether these rhythms are long-term individual characteristics. In nine healthy subjects aged 19-23 years the blood pressure and the finger blood flow were recorded by indirect continuous methods, together with cardiac intervals and respiratory movements. These recordings were repeated in each subject after 1 year. The power spectra of all the parameters recorded were calculated for 5-min periods. The shape of spectra and the division of power into four ranges of frequencies were compared to the spectra recorded after 1 year in each subject and the degree of similarity was evaluated by means of correlation analysis. The average measures of similarity (correlation coefficients) were high, cardiac intervals 0.527, systolic pressure 0.782, pulse pressure 0.755, diastolic pressure 0.709, mean blood pressure 0.673, blood flow 0.818 and respiration 0.627. All these values were higher than values obtained by comparison of spectra of two individuals chosen randomly. The differences were statistically significant for cardiac intervals (Wilcoxon test: P less than 0.05), pulse pressure (P less than 0.05) and respiration (P less than 0.01). These results have shown that interindividual variability of circulatory and respiratory spectra was greater than the intraindividual one. The resting circulatory rhythms are very stable individual features.