Coexistence of OSA may compensate for sleep related reduction in neural respiratory drive in patients with COPD

Abstract

BackgroundThe mechanisms underlying sleep-related hypoventilation in patients with coexisting COPD and obstructive sleep apnoea (OSA), an overlap syndrome, are incompletely understood. We compared neural respiratory drive expressed as diaphragm electromyogram (EMGdi) and ventilation during stage 2 sleep in patients with COPD alone and patients with overlap syndrome.MethodsEMGdi and airflow were recorded during full polysomnography in 14 healthy subjects, 14 patients with OSA and 39 consecutive patients with COPD. The ratio of tidal volume to EMGdi was measured to indirectly assess upper airway resistance.ResultsThirty-five patients with COPD, 12 healthy subjects and 14 patients with OSA completed the study. Of 35 patients with COPD, 19 had COPD alone (FEV1 38.5%±16.3%) whereas 16 had an overlap syndrome (FEV1 47.5±16.2%, AHI 20.5±14.1 events/hour). Ventilation (VE) was lower during stage 2 sleep than wakefulness in both patients with COPD alone (8.6±2.0 to 6.5±1.5 L/min, p<0.001) and those with overlap syndrome (8.3±2.0 to 6.1±1.8 L/min). Neural respiratory drive from wakefulness to sleep decreased significantly for patients with COPD alone (29.5±13.3% to 23.0±8.9% of maximal, p<0.01) but it changed little in those with overlap syndrome. The ratio of tidal volume to EMGdi was unchanged from wakefulness to sleep in patients with COPD alone and healthy subjects but was significantly reduced in patients with OSA or overlap syndrome (p<0.05).ConclusionsStage 2 sleep-related hypoventilation in COPD alone is due to reduction of neural respiratory drive, but in overlap syndrome it is due to increased upper airway resistance.

COPD+OSA: can two bad things be good for you?

“…The findings of He et al 7 raise several questions. Why does neural drive during sleep behave differently in the three clinical conditions?…”

“…He et al 7 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.…”

“…In patients with COPD, neural drive decreases by 20%–30% during NREM sleep7 9 and by about 50% during REM sleep 9. Elevated drive during wakefulness9 10 along with sleep-related reduction in hypercapnic chemosensitivity11 underpin this decrease in drive during sleep in COPD 9 10.…”

“…Elevated drive during wakefulness9 10 along with sleep-related reduction in hypercapnic chemosensitivity11 underpin this decrease in drive during sleep in COPD 9 10. In patients with OSA, increased drive during sleep is a physiological response to increased upper airway resistance 7 12. As for patients with overlap syndrome, the data of He et al 7 suggest that the COPD-associated decrease in drive is cancelled out by the OSA-associated increase in it 7.…”

“…In patients with OSA, increased drive during sleep is a physiological response to increased upper airway resistance 7 12. As for patients with overlap syndrome, the data of He et al 7 suggest that the COPD-associated decrease in drive is cancelled out by the OSA-associated increase in it 7. The result is that in patients with overlap syndrome, neural drive during sleep is as high as that recorded during sleep in OSA, yet of the same magnitude recorded during wakefulness in COPD 7.…”