The interplay between sleep and neural respiratory drive in COPD: contribution of semi-automated analysis of long duration recordings

Neural respiratory drive (NRD) is a clinically relevant biomarker in patients with chronic obstructive pulmonary disease (COPD). However, its analysis is challenging due to several technical considerations, including the need to obtain a stable recording over a short time period. However, a short recording duration may be inadequate to comprehensively record clinically relevant information, particularly during sleep, because NRD varies across sleep stages and over time. In the present study, we evaluated the outcomes of an automatic analysis of NRD data from electromyography (EMG) recordings of neck inspiratory muscles during sleep in COPD patients. This retrospective post hoc cohort analysis was based on a previously published study. Respiratory cycles were determined based on inspiratory peaks. The area under the curve (AUC) and peak values of EMG signals from neck inspiratory muscles (EMGNIM) were extracted for each respiratory cycle and normalized using awake EMGNIM. Polysomnographic data from 26 patients and 9 healthy volunteers were analysed. Contrary to healthy volunteers, COPD patients show a clear EMGNIM activity time-locked to inspiration. The normalized EMGNIM AUC was lower during N2 (48% [30-80], p < 0.001), N3 (47% [27-68], p < 0.001), and REM (38% [21-56], p < 0.001) sleep stages. Similar results were observed for EMGNIM peak. We found that the AUC and peak of EMGNIM in all sleep stages were negatively correlated with the total sleep time, sleep efficiency, and N3 sleep duration (min). Coherence analyses show that the EMGNIM correlate with EEG activity for COPD patients, even during sleep. This correlation is particularly strong for beta and gamma frequencies and Granger Causality suggests the relationship is driven by brain activity. Automatic analysis of EMG signals is feasible and clinically useful for prolonged recording periods across various vigilance states. Respiratory adaptions to COPD are preserved during sleep and could be cortically-mediated.