Cardiorespiratory interactions during slow (<0.4 Hz) changes of respiratory activity

In this work the authors used a multi-parametric approach and spectral analysis techniques to investigate cardio-respiratory interactions during spontaneous Periodic Breathing (PB) in 30 chronic heart failure patients and volitional PB in 16 normal subjects. The authors acquired supine resting recordings of instantaneous lung volume (ILV), heart rate, O₂ saturation at the ear and systolic and diastolic arterial pressure. An instantaneous tidal volume signal was derived from the ILV signal. In both groups the authors found strong evidence of a generalized cardiorespiratory rhythm at ≈0.02 Hz, the frequency of PB, which accounted for most of the variability of all cardiovascular signals. Phase and timing relationships between signals at the frequency of PB were markedly different in the two groups providing important insights into the complex links between respiration and circulation at very low (<0.04 Hz) frequencies