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COPD and obstructive sleep apnoea (OSA), two highly prevalent disorders,1 are both associated with substantial sleep-related hypoventilation.2 Sleep-related hypoventilation in these patients is of greater magnitude than that recorded in healthy subjects. These observations raise the possibility that patients concurrently affected by COPD and OSA, also known as overlap syndrome, may develop worse sleep-related hypoventilation than patients with COPD or OSA alone. When sufficiently severe, sleep-related hypoventilation can reset the chemoreceptor threshold with resultant daytime hypercapnia.3 This (hypothetical) chain of events could explain why, despite less severe airway obstruction, the prevalence of daytime hypercapnia in patients with overlap syndrome is greater than that in patients with COPD4 or OSA alone.5 More profound hypercapnia and nocturnal hypoxaemia might also explain the reported increase in mortality in overlap syndrome compared with COPD.6
He et al7 advance our understanding of the mechanisms of sleep-related hypoventilation in overlap syndrome. Specifically, and for the first time, the investigators compare the neural respiratory drive and ventilation during non-rapid eye movement (NREM) sleep in overlap syndrome against drive and ventilation in COPD alone, OSA alone and in healthy subjects. Neural respiratory drive was quantified as the amplitude of the diaphragm electromyogram signal (EMGdi) recorded with oesophageal electrodes.8 To assess upper airway resistance, the investigators computed the ratio of tidal volume to EMGdi.9
As expected, minute ventilation during sleep decreased in all participants: 10% in healthy subjects, 24% in COPD, 21% in OSA and ‘only’ 27% in patients with overlap syndrome. This lack of synergy between COPD and OSA in worsening sleep hypoventilation resulted from the unique response …
Contributors Both authors confirm that they have fulfilled the following criteria: substantial contribution to the conception of the editorial and drafting and revising it critically for important intellectual content and final approval of the version to be published. Both authors agree to be accountable for all aspects of the editorial.
Funding VA Research Service.
Competing interests FL’s research laboratory has received research grants from the National Institutes of Health, VA Research Service, Liberate Medical LLC, and the National Science Foundation. RLO's research laboratory has received research grants from the National Institutes of Health. In addition, RLO has received honoraria and travel reimbursement from ResMed and Itamar Medical (each <$5000).
Provenance and peer review Commissioned; internally peer reviewed.
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