Doses and agents used for chemotherapy will be determined by a patient's primary treating hematologist according to standard treatment guidelines (Neupogen and plerixafor). The experimental intervention will be inclusion of daily HBO2 (2.4 ATA for 90 minutes) administered for 3-5 days. Assessment of blood progenitor cell mobilization will follow standard clinical evaluations and protocols. No additional interventions will be performed. The only addition to standard clinical analysis will be obtaining an extra 4 ml tube of blood at each phlebotomy session for studies to be performed in the PI's lab including analysis of progenitor cell sub-types, content of hypoxia inducible factors and activity of nitric oxide synthase-3 in platelets following published methods (3).