The purpose of this study is to determine if hyperbaric oxygen therapy is safe in the setting of stem cell transplantation. This study will also determine if hyperbaric oxygen therapy improves engraftment, graft versus host disease, neutrophil count, and incidence and severity of mucositis (inflammation of the mouth or gut) and infection. This study has two cohorts. The first cohort is subjects with acute myeloid leukemia (AML) or Myelodysplastic Syndrome (MDS). The second cohort is subjects with chronic myelomonocytic leukemia (CMML), atypical chronic myeloid leukemia (aCML), chronic monocytic leukemia, chronic neutrophilic leukemia (CNL), myelofibrosis, and myelodysplastic/myeloproliferative (MDS/MPN) overlap syndrome. The first cohort has completed the recruitment so only the second cohort will be recruited.

Inclusion Criteria:

• Voluntary written informed consent
• Men or women, age ≥ 18 years of age, with upper limit of 75 years old.
• Subjects with acute myeloid leukemia (AML) or Myelodysplastic Syndrome (MDS) for cohort 1.
• Subjects with chronic myelomonocytic leukemia (CMML), atypical chronic myeloid leukemia (aCML), CML, chronic neutrophilic leukemia (CNL), myelofibrosis, and myelodysplastic/myeloproliferative (MDS/MPN) overlap syndrome for cohort 2.
• Karnofsky performance status (KPS) of ≥ 70%
• Patients should have New York Heart Association (NYHA) Functional Classification, Class I (ordinary physical activity does not cause undue fatigue, palpitation, dyspnea, or anginal pain) or Class II (ordinary physical activity results in fatigue, palpitation, dyspnea, or anginal pain).
• Adequate hepatic, renal, cardiac and pulmonary function to be eligible for transplant. Minimum criteria include: Hepatic: ALT, AST < 4x IULN and serum total bilirubin ≤ 2.0 mg/dL; Renal: serum creatinine: ≤ 2.0 mg/dL; Left ventricular ejection fraction ≥ 45% measured by 2D-ECHO or MUGA scan; EKG with no clinically significant arrhythmia; FEV1, FVC and DLCO ≥ 50% of predicted value (corrected to serum hemoglobin)
• Women of child-bearing potential and men with partners of child-bearing potential must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry, for the duration of study participation, and for 30 days following completion of therapy. Should a woman or partner become pregnant or suspect she is pregnant while participating in this study, she should inform her treating physician and the investigator immediately.
• A woman of child-bearing potential is any female (regardless of sexual orientation, having undergone a tubal ligation, or remaining celibate by choice) who meets the following criteria: Has not undergone a hysterectomy or bilateral oophorectomy; or Has not been naturally postmenopausal for at least 12 consecutive months (i.e., has had menses at any time in the preceding 12 consecutive months)
• Women of child-bearing potential should have a negative urine or serum pregnancy test within 4 weeks of starting preparative regimen

Exclusion Criteria:

• Pregnant or breastfeeding
• Severe chronic obstructive pulmonary disease requiring oxygen supplementation
• History of spontaneous pneumothorax, prior chest surgery requiring thoracotomy or direct chest irradiation to the lungs
• Evidence of pneumothorax or significant pulmonary fibrosis on chest imaging within 60 days of transplant.
• Active malignancy excluding AML, MDS, CMML, aCML CML, CNL, MF and MDS/MPN overlap syndrome.
• Active ear/sinus infection. Patients with chronic sinusitis or sinus headaches are excluded unless cleared by ear, nose, and throat specialist.
• Recent sinus surgery (within the last 5 years).
• Ear surgery excluding myringotomy or ear tubes
• Subjects must agree to refrain from active tobacco or e-cigarette use 72 hours prior to transplant until complete transplant recovery. Nicotine replacement therapy is allowed.
• Claustrophobia
• History of recurrent seizures within 5 years of study enrollment.
• Uncontrolled asthma
• Uncontrolled viral or bacterial infection at the time of study enrollment
• Active or recent (prior 6 months) invasive fungal infection without interdisciplinary (ID) consult and approval
• Patients who had intrathecal chemotherapy within 2 weeks of starting preparative regimen or cranial irradiation within 4 weeks of starting preparative regimen

All individual participant data collected during the trial will be shared after deidentification, including dictionaries.

Data will be available immediately following publication. No end date.

Anyone who wishes to access the data for any type of analyses.