Inclusion Criteria: Inclusion criteria include GOLD stage 3 or 4 for outpatients and for in-patients, criteria will include an admission diagnosis of AECOPD, age greater than 18 years, ability to participate in a supine sleep study, known COPD diagnosed by a pulmonologist (GOLD stage 3 or 4). Informed consent will be obtained from each patient. The study population will be composed of patients admitted to Gagnon 3 from the emergency department (ED) and to 10 CD from the ED. All new admissions to Gagnon 3 at MMC and 10 CD at OMC will be screened daily by study personnel for enrollment using the author's inclusion and exclusions criteria. Permission to approach patients and families will be requested from the attending pulmonologist.  -  Exclusion Criteria: a. List exclusion criteria:  We excluded patients unable or unwilling to participate in the home sleep study, medical problems or medications affecting the diagnostic accuracy/application of WatchPAT One (peripheral vascular disease, peripheral neuropathy, alpha blockade), admission to the ICU, finger deformity which prevented adequate sensor application.  -