Introduction:Slecp hypoventilation is proposed to contribute to daytime hypercapnia in severe COPD. We sought to assess factors predictive of severity of sleep hypoventilation, and whether severity was predictive of night-to-moming change in pCC 2. Methods: Full polysomnography including transcutaneous C02 (TcC02) was performed in 78 subjects with stable severe COPD (mean (± SD) FEV1 24±10 % predicted, Pa02 on air 51.8±9.2 mmHg, PaC02 55.4i7.4 mmHg ) without sleep apnea (AHI 20/h). All were on long term 02 therapy, and were studied on their usual 02 flow rate. Evening and morning ABG were measured and TcC02 sensor drift corrected by correlation with simultaneous PaCU2. Detailed lung function assessment was performed and BMI calculated. Severity of sleep hypoventilation was assessed by i) % of total sleep time spent at TcCO2 >10mmHg above baseline (%TST>10) ii) maximal increment in TcCO2 above baseline (maxincr), iii) slope of rise in TcCO2 on entry into REM (REMslo). Results: BMI (but not lung function or baseline ABG) was correlated with Maxincr (r=0.3) and remained in the model on multivariate analysis. REMslo correlated weakly with pO2 on air, with pCO2 and with O2 flow rate. Only O2 flow remained in the model on multivariate analysis. None of the variables was predictive of TST%>10. PaCO2 rose significantly between evening and morning (59.8±IO,3 to 65.0 ±12.2 p<0.001). The evening to morning increase in PaCO2 correlated with baseline PaC02 on air (r=0.38), with %TST>10 (r=0.56), and with maxincr (r=0.56) (both p0.0001), but not with REMslo. On multivariate analysis only pCO2 on air and TST%>10 remained in the model. Conclusion: These results suggest sleep hypoventilation in hypercapnic COPD increases with increasing BMI and, in REM sleep, with increasing FIO2. Sleep hypoventilation is associated with a rise in night-to-morning PaCO2 Analysis is proceeding to determine the influence of inspiratory flow limitation and alcohol consumption on sleep hypoventilation.
|Issue number||SUPPL. 1|
|Publication status||Published - 1 Dec 2001|