Hydrogen gas may decrease the degree or incidence of brain injury following ischemia. The purpose of this study is to determine the safety and tolerability of inhaled hydrogen gas at the dose exposures required for a clinical efficacy study in healthy adult participants. Participants will breathe a gas mixture that contains a low concentration of hydrogen gas in air through a high flow nasal cannula. Investigators will test for any changes in breathing and neurologic status, as well as lab tests during and following the exposure period.

Inhaled hydrogen gas (H2) has been shown to have significant protective effects on ischemic organs. Clinical trials abroad have shown promise that treatment of patients suffering from stroke, cardiac arrest, or heart attacks may benefit from inhaling hydrogen gas during the early recovery period.

The purpose of this study is to determine the safety and tolerability of inhaled hydrogen gas at the dose exposures required for a clinical efficacy study in healthy adult volunteers.

Study design. Eight (8) healthy adult participants will be recruited from the greater Boston area for this study. Consenting participants will be admitted to the hospital and will undergo a series of screens (questionnaires, examination, tests) to ensure suitability to participate. Eligible and consenting participants will then undergo exposure to 2.4% H2 in medical air via high flow nasal cannula for either 24 (n=2), 48 (n=2) or 72 (n=4) hours. Participants will be screened for adverse effects as follows: vital signs every 8 hours, nursing assessment of symptoms (codified based on the National Cancer Institute's Common Terminology Criteria for Adverse Events, CTCAE) every 8 hours, bedside spirometry daily, mini-mental state exam daily, physician physical exam daily, and serum testing (blood count, chemistry, liver and coagulation profile, venous blood gas) following exposure period.

Inclusion Criteria:

1. Age 18 to 35
2. Able to remain inpatient for duration of admission (24-72 hours)

Exclusion Criteria:

1. History of any chronic illness, including respiratory disorders such as asthma, chronic obstructive pulmonary disease, prior acute lung injury or acute respiratory distress syndrome;
2. Inflammatory disorders, such as lupus erythematosus, inflammatory bowel disease;
3. Heritable disorders, such as trisomy 21, cystic fibrosis;
4. Mitochondrial disorders;
5. Currently smoking cigarettes or have a history of smoking cigarettes;
6. The regular use of prescription medications (except for contraceptive medications) within 30 days of enrollment;
7. Any lifetime inpatient hospitalization for respiratory illness;
8. Pregnancy.

Each duration group will be 50% male and 50% female.

The data will be shared only with the FDA and members of the DSMB and IRB.