Clinical Research Directory

Inclusion Criteria: * 18 - 64 years-old volunteers. * Body Mass Index (BMI) 18 - 30 kg/m2. * Absence of current systemic and/or respiratory diseases. * Capacity to consent to the study. Exclusion Criteria: * Evidence of any physical, mental, and/or medical conditions that would make the proposed studies relatively more hazardous. * Systemic and/or respiratory disease with or without any functional limitation. * Left ventricle ejection fraction \< 30%. * Baseline MetHb ≥ 3% * Other conditions of increased risk for MetHb formation: genetic diseases (e.g., glucose-6-phosphate dehydrogenase deficiency, cytochrome b5 reductase deficiency, sickle cell disease), significant anemia or baseline elevation in MetHb. * History of transient ischemic attack or stroke. * Active smoking and tobacco chewers. Volunteers may be enrolled if they quit smoking for more than 1 year and less than 10 pack years total. * Any vaping/e-cigarettes use * Excess alcohol use: more than ½ L/day of wine consumption or equivalent * Current use of any recreational drugs (including the use of medical marijuana) or use of recreational drugs over the past year. * Pregnancy determined by blood pregnancy test detecting presence of human chorionic gonadotropin (hCG). * Less than six weeks postpartum. * Any current medication uses except oral contraceptives. * Lower respiratory infection within the last 30 days. * Claustrophobia (inability to wear a facemask) or other active psychiatric conditions or unwillingness to cooperate with the investigators and other medical teams. * Currently enrolled in another research study. * Facial abnormalities that would preclude proper use of a face mask.