In this small pilot study, participants (patients and healthy volunteers) will have blood drawn before and after the study intervention (hyperbaric chamber session or normal pressure oxygen breathing. This blood will be analyzed for neutrophil oxidative burst and cytokine analysis.

The investigators are interested in studying the influence of hyperbaric oxygen on neutrophils (a kind of white blood cell) and cytokines (cell proteins). Hyperbaric oxygen can enhance the way the immune system works, but the investigators don't fully know how that happens. the investigators are doing this study to learn more about this question.

Cohort 1: Diabetic hyperbaric patients with active, chronic infection

Inclusion Criteria:

• Adult patients (ages 18-65) presenting for an anticipated course of at least 4 hyperbaric oxygen sessions for chronic clinical indications (possible indications include diabetic lower extremity wounds or refractory osteomyelitis)
• Diabetes mellitus
• Current antibiotic use for active infection

Exclusion Criteria:

• Prior treatment with hyperbaric oxygen within the last 30 days
• Consistent vitamin C or vitamin E supplementation in the past year
• Active tobacco use
• Pregnancy

Cohort 2: Hyperbaric patients without diabetes or active infection

Inclusion Criteria:

- Adult patients (ages 18-65) presenting for an anticipated course of at least 4 hyperbaric oxygen sessions for chronic clinical indications (possible indications include crush injury, acute peripheral arterial insufficiency, or radiation necrosis)

Exclusion Criteria:

• Prior treatment with hyperbaric oxygen within the last 30 days
• Consistent vitamin C or vitamin E supplementation in the past year
• Active tobacco use
• Pregnancy
• Diabetes mellitus
• Known or suspected viral or bacterial infection

Cohort 3: Critically ill hyperbaric patients with acute infection

Inclusion Criteria:

- Adult patients (ages 18-65) admitted to the intensive care unit for acute, life-threatening infection where hyperbaric oxygen is clinically indicated for at least 4 sessions (possible indications include gas gangrene or necrotizing fasciitis)

Exclusion Criteria:

• Prior treatment with hyperbaric oxygen within the last 30 days
• Consistent vitamin C or vitamin E supplementation in the past year
• Active tobacco use
• Pregnancy

Cohort 4:

Carbon monoxide-poisoned patients

Inclusion Criteria:

- Adult patients (ages 18-65) presenting for hyperbaric oxygen for acute carbon monoxide poisoning (up to 3 sessions)

Exclusion Criteria:

• Prior treatment with hyperbaric oxygen within the last 30 days
• Consistent vitamin C or vitamin E supplementation in the past year
• Active tobacco use
• Pregnancy
• Time interval between removal from carbon monoxide source and first hyperbaric oxygen session >12 hours

Cohort 5: Diabetic research subjects also undergoing glucose tolerance testing

Inclusion Criteria:

• Co-enrollment in glucose tolerance testing study
• Meet inclusion/exclusion profile for that study

Exclusion Criteria:

• Prior treatment with hyperbaric oxygen within the last 30 days
• Consistent vitamin C or vitamin E supplementation in the past year
• Active tobacco use

Cohort 6: Brain injury research subjects

Inclusion Criteria:

• Co-enrollment in brain injury study
• Meet inclusion/exclusion profile for that study

Exclusion Criteria:

• Known or suspected viral or bacterial infection
• Consistent vitamin C or vitamin E supplementation in the past year
• Active tobacco use

Cohort 7: Hyperbaric chamber inside attendants

Inclusion Criteria:

- Employees (ages 18-65) medically cleared to work as hyperbaric chamber inside attendants, reporting for a regular duty day

Exclusion Criteria:

• Known or suspected viral or bacterial infection
• Consistent vitamin C or vitamin E supplementation in the past year
• Active tobacco use
• Prior work in the hyperbaric chamber in the last 72 hours

Cohort 8: Healthy volunteers to receive hyperbaric oxygen

Inclusion Criteria:

• Healthy volunteers (ages 18-65)
• Medical clearance for hyperbaric oxygen exposure

Exclusion criteria:

• Hyperbaric oxygen exposure within the last 30 days
• Active chronic medical condition
• Use in the past 30 days of any over-the-counter or prescription medication or dietary supplement beyond a general multivitamin
• Active tobacco use
• History of significant health problems, including metabolic bone disease, skeletal muscle pathologies, cardiac or peripheral cardiovascular system abnormalities, clotting disorders, coronary artery disease, peripheral vascular disease, stroke, cancer, high cholesterol or triglycerides, high blood pressure, diabetes mellitus, or impaired liver/kidney function.
• Morbidly obese (body mass index > 40 kg/m2)
• Pregnancy
• Known or suspected viral or bacterial infection

Cohort 9: Healthy volunteers to breathe 100% oxygen at atmospheric pressure

Inclusion Criteria:

- Healthy volunteers (ages 18-65)

Exclusion criteria:

• Hyperbaric oxygen exposure within the last 30 days
• Active chronic medical condition
• Use in the past 30 days of any over-the-counter or prescription medication or dietary supplement beyond a general multivitamin
• Active tobacco use
• History of significant health problems, including metabolic bone disease, skeletal muscle pathologies, cardiac or peripheral cardiovascular system abnormalities, clotting disorders, coronary artery disease, peripheral vascular disease, stroke, cancer, high cholesterol or triglycerides, high blood pressure, diabetes mellitus, or impaired liver/kidney function.
• Morbidly obese (body mass index > 40 kg/m2)
• Pregnancy
• Known or suspected viral or bacterial infection