ASSESSMENT OF FREQUENCY-SHIFTS IN R-R INTERVAL VARIABILITY AND RESPIRATION WITH COMPLEX DEMODULATION

A complex demodulation (CDM) method for continuous assessment of frequ ency shifts and time-dependent changes in amplitude in the rhythmic co mponents existing in predefined frequency bands was proposed and appli ed to the analysis of high-frequency (HF) and low-frequency (LF) compo nents of the R-R interval and to the analysis of respiration via imped ance spirogram. Simulation studies revealed that this CDM technique fu rnishes mathematical features well suited to the investigation of non stationary R-R interval signals and can delineate time-dependent fluct uations in both amplitude and frequency, accurately differentiating be tween HF and LF components. Analysis of data during paced breathing at different respiratory frequencies revealed that the estimated frequen cy of the HF component and respiration faithfully reflected the freque ncy of paced breathing. Analysis of data during dynamic exercise with in creasing workload (20 W/min) showed that the frequency of the HF co mponent was elevated with exercise and that both HF and LF amplitudes were reduced progressively with advancing load. CDM-derived frequency and amplitude of respiration were highly correlated to direct breath-b y-breath respiratory frequency and tidal volume measurements. We concl ude that this method could provide a powerful means for continuously a ssessing time-dependent changes in both cardiovascular and respiratory variations.