Cardiorespiratory coupling during sleep in difficult-to-control asthmatic patients

Heart rate variability (HRV) and respiration recorded during sleep from 8 patients suffering from difficult-to-control asthma were studied to investigate autonomic nervous system control of cardiac and respiratory activities, and of cardio-respiratory coupling during different sleep stages. In healthy subjects, HRV monitoring during sleep reveals a predominant parasympathetic drive to the heart during nonrapid eye movement (NREM) sleep and an increased sympathetic activity during rapid eye movement (REM) sleep. Spectral analysis of HRV and cross-spectral analysis of HRV and respiration signals in the analyzed difficult-to-control asthma patients showed trends in the main spectral indices, which appeared similar to variations observed in non pathologic subjects, but which were possibly affected by a reduction in the sympathetic and cardiorespiratory modulations. The ratio between the tachogram power in the low frequency (LF) band and the tachogram power in the high frequency (HF) band, a marker of the sympatho-vagal balance, increased during deep sleep stage S3 (LF/HF = 0.855 ± 0.876, mean ± s.d.), indicating a predominance of the sympathetic component, and decreased during REM sleep (LF/HF = 0.748 ± 0.716, mean ± s.d.), indicating a drift of the sympatho-vagal balance towards the vagal component. The coherence between the tachogram and the respirogram in the HF band increased during deep sleep stages S2 (coherence = 0.855 ± 0.727, mean ± s.d.) and S4 (coherence = 0.843 ± 0.724, mean ± s.d.) and decreased during REM sleep (coherence = 0.808 ± 0.719, mean ± s.d.), suggesting that a stronger cardiorespiratory coupling was reached with synchronization of sleep.