RESEARCH PLAN: The investigators will study if elderly Veterans with OSA and comorbid COPD have increased neurocognitive deficits and sleepiness with reduced quality of life compared to patients with either OSA or COPD alone (Aim 3) and whether treatment with PAP/NIPPV and supplemental oxygen compared to CPAP alone in elderly Veterans with moderate-to-severe OSA and concomitant moderate-to-severe COPD will improve cognitive function, sleepiness and quality of life (QoL).