The Cardiovascular Consequences of Sleep Apnea Plus COPD (Overlap Syndrome)

Inclusion Criteria: * Provision of signed and dated informed consent form. * Stated willingness to comply with all study procedures and availability for the duration of the study. * Persons aged 40-79. * For women, only postmenopausal women will be included * Diagnosed with untreated moderate to severe obstructive sleep apnea (apnea-hypopnea index ≥15 events/hr and ≤80 events/hr) and/or diagnosed with COPD with FEV1/FVC ratio \<0.7 and will be on stable medications as assessed by a board-certified pulmonologist. Exclusion Criteria: * Premenopausal women (i.e. women are pregnant or may become pregnant) or lactation * Presence of specific devices: cardiac implantable electronic device (CIED) such as pacemakers, implantable cardioverter defibrillators (ICDs) and cardiac resynchronization therapy (CRT) devices, metallic foreign bodies, implantable neurostimulation systems, cochlear implants/ear implant, drug infusion pumps (insulin delivery, analgesic drugs, or chemotherapy pumps), metallic fragments such as bullets, shotgun pellets, and metal shrapnel , cerebral artery aneurysm clips, magnetic dental implants, and artificial limb. * Known allergic reactions to components of the study intervention: (if getting contrast, MRI contrast (gadolinium)). * Concurrent severe sleep disorders (such as periodic limb movements, restless legs syndrome, narcolepsy, idiopathic hypersomnia, etc). * Exhibit Cheyne-Stokes respiration or central sleep apnea (\> 25 % of events central) * Take potentially confounding medications or hormones that affect breathing. * Subjects will be excluded if they are deemed medically unstable with active neurological, cardiac, liver, endocrine, and infectious diseases. * We will also exclude participants with pulmonary disease apart from COPD. * We will exclude participants with active cancer treatment. * We will exclude azotemia (estimated glomerular fraction rate \< 30ml/min) as there is some concern about giving gadolinium to these patients (if getting contrast MRI). * people with exposures deemed to be problematic for the research e.g. any smoking in bedroom by participant or household member, major second-hand smoke, e-cigarettes, tetrahydrocannabinol, major drug or alcohol consumption (\>3 oz/day) and other environmental pollution effects (indoor and outdoor). * Individuals who are already on continuous O2 for COPD or PAP treatment for OSA. * Patients with sustained desaturations below 89% during wake time will be excluded for ethical reasons since withholding oxygen in hypoxemic patients would be at odds with standard of care. * Individuals with OSA (AHI range 15-80/hr) will be screened for pathological sleepiness and will be excluded if ESS \>18/24, history of motor vehicle accident or near miss accident, or high-risk occupation. * COPD individuals with arterial PCO2 higher than 52 mmHg will be excluded. * Individuals who are currently incarcerated.