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



EMGdiand 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 EMGdiwas measured to indirectly assess upper airway resistance.



Thirty-five patients with COPD, 12 healthy subjects and 14 patients with OSA completed the study. Of 35 patients with COPD, 19 had COPD alone (FEV138.5%±16.3%) whereas 16 had an overlap syndrome (FEV147.5±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 EMGdiwas 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).



Stage 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.
State Key Laboratory of Respiratory Disease, Guangzhou Medical University, Guangzhou, China.
Bai-Ting
BT
He
Jiangsu Provincial Official Hospital, Nanjing, China.
Gan
G
Lu
State Key Laboratory of Respiratory Disease, Guangzhou Medical University, Guangzhou, China.
Si-Chang
SC
Xiao
Department of Respiratory Medicine, Second Affiliated Hospital of Soochow University, Suzhou, China.
Rui
R
Chen
Faculty of Life Sciences and Medicine, King's College London, London, UK.
Joerg
J
Steier
Faculty of Life Sciences and Medicine, King's College London, London, UK.
John
J
Moxham
NIHR Respiratory Biomedical Research Unit, The Royal Brompton and Harefield NHS Foundation Trust and Imperial College, Royal Brompton Hospital, London, UK.
Michael I
MI
Polkey
State Key Laboratory of Respiratory Disease, Guangzhou Medical University, Guangzhou, China.
Yuan-Ming
YM
Luo
D003964:Diaphragm / Q000503:physiopathology*; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017286:Polysomnography; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications* / Q000503:physiopathology*; D012129:Respiratory Function Tests; D012137:Respiratory System / Q000503:physiopathology; D020181:Sleep Apnea, Obstructive / Q000150:complications* / Q000503:physiopathology*; D013577:Syndrome
COPD ÀÜ Mechanisms; Respiratory Muscles; Sleep apnoea