The coherence spectrum for quantifying beat-to-beat adaptation of RT intervals to heart rate in normal subjects and in postinfarction patients

This paper studies the frequency modulation of RT-interval variability and its common variations to the RR-interval signals in 21 normal subjects and in 49 patients after myocardial infarction. The coherence function was used to measure these common variations. Additionally, the spectral analysis of R-wave amplitude variability was performed to obtain the respiratory frequency. The coherence spectrum revealed the greatest relation between RRV and RTV in the range of high frequencies (0.24 Hz in controls, 0.27 Hz in patients). The magnitude of the coherence spectra were only slightly lower in patients (0.649+/-0.211), as compared to controls (0.806+/-0.163). The means of coherence spectra correlated significantly to the respiratory rate (R=0.79).