Inclusion Criteria:  Adult patients requiring an unplanned hospitalization or emergency room visit due to an acute hypercapnic respiratory failure exacerbation (AHRF), not on home noninvasive or invasive ventilation, neuromuscular disease (e.g., spinal cord injury) or central nervous system disorders (e.g., cerebral vascular accident, Alzheimer), absence of tracheotomy, and non-morbidly obese.  Exclusion Criteria:  Patients with AHRF due to drug overdose Ventilatory support (noninvasive or invasive ventilation) is needed before or during the sleep studies or if an acute deterioration (e.g., cerebral vascular accident, cardiac arrest) happens before or during the sleep studies.