Supine hyperinflation and expiratory flow limitation are associated with respiratory arousals and nocturnal hypoventilation in COPD.

INTRODUCTION

Subjective sleep disturbance is common in chronic obstructive pulmonary disease (COPD) and is related to hyperinflation when supine and tidal expiratory flow limitation (EFL). We hypothesised that abnormalities in supine lung mechanics disturb sleep and impair gas exchange in COPD. We aimed to assess relationships between supine lung derecruitment, EFL and hyperinflation, and polysomnographic measures of sleep disturbance and gas exchange in COPD.

METHODS

In this prospective, observational study, supine oscillometry was performed in stable COPD patients to assess lung derecruitment (reactance at 5 Hz (Xrs5) z-score) and EFL (difference between mean inspiratory and expiratory reactance (∆Xrs5)). Hyperinflation was assessed by supine inspiratory capacity (ICsupine) z-score. In-laboratory polysomnography was used to assess sleep disturbance, measured by Apnoea-Hypopnoea Index (AHI), Oxygen Desaturation Index (ODI) and AHI during rapid eye movement sleep (AHI REM). Monitoring of transcutaneous carbon dioxide (TcCO2), and measurements of partial pressure of arterial carbon dioxide (PaCO2) and HCO3 - were performed in a subgroup.

RESULTS

28 COPD patients were enrolled (13 female, mean age (SD) 67.5 (8.71) years and mean forced expiratory volume in 1second (FEV1) z-scores (SD) -2.61 (1.06)). Worse Xrs5(supine) correlated with greater respiratory arousals (AHI rs =0.47, p=0.01; ODI rs=-0.58, p=0.001), as did greater ∆Xrs5(supine) (AHI REM rs=0.53, p=0.005). Xrs5(supine) correlated with peripheral oxygen saturation nadir (rs=0.43, p=0.02). ICsupine correlated negatively with hypoventilation (PaCO2 rs=-0.77, p=0.001; HCO3 - rs=-0.78, p=0.001, n=15), as did Xrs5(supine) (rise in TcCO2 rs=-0.65, p=0.009).

CONCLUSION

Lung derecruitment, EFL and supine hyperinflation likely contribute to sleep disturbance and sleep-related gas exchange impairment in COPD.