4. a reduction in the number of nocturnal arousals may improve the quality of sleep. Nevertheless, none of these mechanisms has been proven and currently there is no evidence that noninvasive positive pressure ventilation (NIPPV) should be given to stable patients with COPD. While several randomised controlled trials (RCT’s) on NIPPV have been published with different outcomes, a recent meta-analysis did not show beneficial effects on blood gasses, lung function, respiratory muscle function and walking distance.