Abstract
We describe an analysis of cardiac and respiratory time series recorded from 189 subjects of both genders aged 16–90. By application of the synchrosqueezed wavelet transform, we extract the respiratory and cardiac frequencies and phases with better time resolution than is possible with the marked events procedure. By treating the heart and respiration as coupled oscillators, we then apply a method based on Bayesian inference to find the underlying coupling parameters and their time dependence, deriving from them measures such as synchronization, coupling directionality and the relative contributions of different mechanisms. We report a detailed analysis of the reconstructed cardiorespiratory coupling function, its time evolution and age dependence. We show that the direct and indirect respiratory modulations of the heart rate both decrease with age, and that the cardiorespiratory coupling becomes less stable and more time-variable.
Highlights
The cardiorespiratory interaction was first observed by Hales [1]
In the case when all RR-intervals are the same, but the T-wave occurs at different times after the R-peak, methods based on the integral pulse frequency modulation (IPFM) model assumption will yield a constant heart frequency, whereas the instantaneous heart frequency (IHF) extracted from the synchrosqueezed wavelet transform (SWT) will be slightly modulated, providing an indication of these small changes
In agreement with earlier works [41,48,49,50], we observed a decrease of IHF variability with age, but no significant correlation with age in instantaneous respiration frequency (IRF) variability or mean respiratory frequency
Summary
The cardiorespiratory interaction was first observed by Hales [1]. Since the associated physiology and physics have been under continuing investigation. We measure the oscillatory functions of heart and respiration, and apply methods drawn from nonlinear science to detect their instantaneous phases and frequencies Once these have been established, we study the interaction between heart and respiration, treating them as self-sustained nonlinear oscillators and investigating their mutual coordination [15,16,17] or synchronization [18,19,20,21,22,23,24,25,26], coherence [27,28,29,30,31,32] and direction of coupling [33,34,35,36], allowing for the fact that the characteristic frequencies, couplings and other interacting characteristics vary in time [37,38]. Measurements, signal pre-processing and statistical analyses are given in the appendices
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