The primary object is to determine the feasibility of treating patients diagnosed with either CIC/PBS or rUTI with daily hyperbaric oxygen for a total of 40 treatment sessions during an 8-10 week time period. We wish to better understand the demand and degree of adherence for daily HBOT in these two patient populations to inform future planning and design of randomized, sham controlled and double-blind studies. Given the refractory nature of these two diagnoses, a secondary objective of this study is to determine if there is symptomatic improvement following HBOT compared to pretreatment symptoms using standardized patient symptomology questionnaires' (Global Response Assessment-GRA and Patient's Overall Rating of Improvement in Symptoms-PORIS questionnaires).

Patient selection will be carried out by the respective co-investigators based on standard disease definitions. CIC/PBS is defined as urinary tract pain or discomfort and dysuria that is present of \> 6 months and is not due to acute urinary tract infection, stones or other pathology. These patients will be identified and recruited by Dr. C. Lowell Parsons, Co-investigator for the study. rUTI is defined as greater than 2 urinary tract infections in 6 month or greater than 3 urinary tract infections in one year. These patient will be identified and recruited by Dr. Emily Lukacz, Co-investigator. Each study will enroll 20 individuals. The study design is an observational pilot study to determine feasibility and limited efficacy. Thus the primary outcomes will be the number of patients that enroll in the study relative to the number offered enrollment and the percentage of individuals completing the prescribed 40 treatment sessions. For the secondary outcome, limited efficacy, each patient's pre-treatment clinical status will be compared to their post treatment clinical status. Thus for the CIC/PBS study both the global response assessment (GRA) and the patient's overall rating of improvement of symptoms (PORIS) will be obtained and comparison between the pre and post treatment scores will be performed. For the UTI study, the time in days to subsequent acute urinary tract infection and total number of acute UTI's during one year following completion of HBOT will be recorded and compared to that individual's prior clinical history. The dosing algorithm to be used is based on the current standard of care for the treatment of radiation cystitis for which 2.4 ATA x 90 minutes is provided daily, 5 days per week. The total duration of treatment can range from 30-60 minutes depending upon the individual patients severity of illness and response to therapy. Patients are routinely reassessed after every 10-20 treatments. Therefore we are planning to provide 2.4 ATA x 90 minutes with 2 air breaks daily, x 5 days per week x 8 weeks total for both CIC/PBS and rUTI patient population. We will allow the 40 treatments to be administered over an 8-10 week time period to provide some degree of scheduling flexibility for patients.

For this feasibility study we will determine the demand as measured by the number of patients accepting the treatment vs the total number of patients offered enrollment. We will determine the percentage successful completion of the 40 prescribed treatment sessions as the primary outcome variable. The results of the symptom questionnaires obtained at the conclusion for HBOT and by follow up telephone survey at 1, 6 and 12 months following completion of HBOT will be the secondary outcome variable. Finally, adverse events will be gathered on this patient population as per routine clinical practice. The incidence and severity of otic barotrauma, hyperoxic myopia, confinement anxiety and generalized seizures will be determined and compared to the same events experienced by the general hyperbaric patient population being treated during the same period of time.

Symptom Survey Instruments Global Response Assessment (GRA) The GRA measures overall improvement with therapy. It is now used as the primary end point in clinical trials of therapies for CIC/PBS. The assessment asks: "As compared to when you started the study \[treatment\], how would you rate your interstitial cystitis symptoms now?" The seven point scale is centered at zero (no change): markedly worse; moderately worse; slightly worse; no change; slightly improved; moderately improved; and markedly improved. Responders will be defined as those individuals with scores falling in the moderately and markedly improved categories.

Patient's Overall Rating of Improvement of Symptoms (PORIS) The PORIS has three questions that address the overall change in CIC/PBS, pain, and urgency after treatment as worse, no better (0% improvement), slightly improved (25%), moderately improved (50%), greatly improved (75%), or symptoms gone (100% improvement). Responders will be defined as those individuals with scores falling into the moderately or greatly improved or no symptoms categories.