A component of normal care at this point is daily injections with a drug called Neupogen. In order to accommodate the needed time for normal clinical procedures with the anticipated time-course for hyperbaric oxygen therapy-induced stem cell mobilization, the study protocol will begin on Thursday with Neupogen injection plus a 90 minute exposure to hyperbaric oxygen at a pressure of 2.4 atmospheres absolute (the normal protocol followed by the Hyperbaric Oxygen [HBO2] Therapy Service for daily treatments of elective patients). Neupogen plus HBO2 will be repeated again on Friday, and on Saturday and Sunday Neupogen injections again administered.