Obstructive Sleep Apnea (OSA) patients are at increased risk of major cardiovascular events, so many patients take aspirin for prevention. Poor responsiveness to aspirin is a major clinical concern because it can potentially worsen the prognosis of OSA patients. However, continuous positive airway pressure (CPAP) therapy that is considered standard of care for OSA treatment may potentially lead to improvement in responsiveness to aspirin. This study will determine whether CPAP therapy decreases patients' aspirin resistance in OSA patients with a new diagnosis or existing moderate to severe OSA who are treated with CPAP and take aspirin for prevention.

Obstructive Sleep Apnea (OSA) is a common sleep-related breathing disorder that afflicts more than 25 million adults in the United States. This number continues to rise yearly due to increased incidence of obesity in the United States. The prevalence of OSA among males and females is also on the rise with 34% of males and 17% of females diagnosed with this disease.

OSA is characterized as intermittent pharyngeal soft-tissue obstruction due to anatomical or positional etiology during sleep. This leads to episodes of hypoxemia and apneas which result in overall sleep fragmentation. The pathophysiology associated with OSA is complex. However, some proposed causes of OSA include hypoxia during sleep which causes increased circulating catecholamines and sympathetic activation, free radical formation leading to oxidative stress, increased cytokine release and endothelial dysfunction. These proposed mechanisms are also associated with increased platelet aggregation and hyperactivity and increase a patient's overall risk for cardiovascular morbidities.

Many patients with cardiovascular co-morbidities are taking aspirin for primary or secondary prevention. With a concomitant diagnosis of OSA, it is thought that these patients who are taking aspirin on a daily basis may become resistant to its effects based on how their OSA is controlled (ie. CPAP vs. Non-CPAP). Although aspirin resistance has been noted to be a "laboratory phenomenon," there have been studies which have shown a three-fold increase in cardiovascularco- morbidities in patients who were found to be aspirin resistant. In this study, it is our goal to determine the prevalence of aspirin resistance in patients who have a diagnosis of OSA and undergoing treatment with CPAP or Non-CPAP methods by measuring Aspirin Resistant Units (ARUs) using light aggregometry. It is our overall objective to determine whether or not OSA is an independent risk factor for aspirin resistance.

OSA patients are at increased risk of major cardiovascular events and aspirin resistance is associated with poor cardiovascular outcomes. Studying aspirin responsiveness in OSA patients may help to elucidate the potential role of platelet function testing, including the possible clinical implications of an aspirin therapy regimen guided by platelet function testing.

Inclusion Criteria for Control Group:

• No OSA (based on home or attended polysomnography) determined by negative sleep study (HSAT or NPSG) REI/AHI < 5 (if a home study was done and found negative or equivocal an attended study is required to rule out sleep apnea)
• Patient is taking aspirin at a dose of 81 mg/day for at least a week last dose taken within 24 hours prior to enrollment.

Inclusion Criteria for "CPAP-Naïve" Cohort:

• Diagnosis of OSA (based on home or attended sleep study) with an REI/AHI ≥ 15 with or without symptoms or REI/AHI ≥ 5 with symptoms of sleep apnea in a patient 18-85 years old.
• Patient is taking aspirin at a dose of 81mg/day for at least a week, last dose taken within 24 hours prior to enrollment.

Inclusion Criteria for "CPAP-treated" Cohort:

• Diagnosis of OSA (based on home or attended sleep study) with an REI/AHI ≥ 15 with or without symptoms or REI/AHI ≥ 5 with symptoms of sleep apnea in a patient 18-85 years old.
• CPAP has been started within the last 2 years
• Patient is taking aspirin at a dose of 81mg/day for at least a week, last dose taken within 24 hours prior to enrollment.

Exclusion Criteria for all cohorts including control group:

• Patient is not able to provide informed consent
• Patient has taken at least one dose of a non-aspirin NSAID within the last 3 days
• Patient has taken at least one dose of another (non-aspirin) anti-platelet agent(s) (clopidogrel, abciximab, eptifibatide, tirofiban, cilostazol, dipyridamole, prasugrel, ticlopidine, ticagrelor) in the last 7 days.
• Patient has taken at least one dose of vitamin K antagonist (warfarin) in the last 7 days or heparin (low molecular weight or unfractionated) in the last 24 hours
• Patient has taken steroids (intravenous, oral, or topical) within the last 2 weeks
• Signs and symptoms of an active infection:
• Temperature ≥ 100.4
• Productive cough
• Rhinorrhea
• Dysuria
• Diarrhea
• Signs and symptoms of a local inflammatory reaction
• Pain
• Warmth
• Erythema
• Swelling
• Any history of a systemic inflammatory disorder
• Any history of diabetes mellitus if no HbA1C measurement obtained within 6 months is available; if HbA1C measurement obtained within 6 months is available, patient will be included.
• Any history of chronic kidney disease
• Pregnant women, and women in labor

Patients who come to the WCHN Pulmonary and Sleep Medicine Clinic either for a follow-up appointment to monitor their therapy for OSA or for an appointment to discuss a new diagnosis of OSA referred by their pulmonologist.