Effects of Obstructive Sleep Apnea and/or Cigarette Smoking on Endothelial Function

Inclusion Criteria: * No acute illness * No hospitalization in past 4 weeks * Absence of medical comorbidity such as hypertension, ischemic heart disease, diabetes and hyperlipidemia, renal impairment, vasculitis or Raynaud's syndrome, peripheral vascular disease especially Buerger's disease, aortic disease (aortic aneurysm or dilatation), cancer, thrombocytopenia, coagulation disorder or other chronic medical illness Exclusion Criteria: * Mentally incapacitated