Cardiorespiratory system dynamics in chronic heart failure

Aims: With the complex demodulation (CDM) method, we assessed the instantaneous amplitude and frequency of cardiovascular (CV) and respiratory oscillations, and the instant phase (IP) between the CV and respiratory signals using respiration as a periodic forced stimulation. We hypothesised a possible lack of synchronisation between CV and respiratory signals under regular breathing at different frequencies. Methods: RR interval (ECG), blood pressure (SBP/DBP, Finapress), respiration (Respitrace) were monitored during two random-order periods of voluntary paced-breathing (0.15 Hz/0.25 Hz) in 10 moderate CHF patients and 10 age-matched controls. The CDM method provides the amplitude and frequency of a particular spectral component as a function of time in both LF and HF bands. IP between CV and respiratory oscillations was assessed using the real modulating breathing rate. Results: (i) Continuous phase variations between CV oscillations and the respiratory signal were evidenced in CHF patients, the slower the breathing rate, the greater the phase variation (RR/Resp; 0.25 Hz, 23 +/- 17degrees; 0.15 Hz, 46 +/- 57degrees, P < 0.01; RR/Resp at 0.15 Hz 6+/-3 vs. 46+/-57 P<0.01 controls vs. CHF). Phase was constant in controls. (ii) In patients, the instant amplitude of the cardiovascular oscillations in the high frequency domain is more markedly altered when the breathing rate was slowed down as compared to controls. Conclusion: The lack of synchronisation between physiological signals during voluntary breathing in CHF patients highlights a central uncoupling between CV and respiratory neuronal activities. (C) 2002 European Society of Cardiology. Published by Elsevier Science B.V. All rights reserved.