A major medical concern is that once oxygen therapy is begun and clinical stability is achieved, further improvements in ABG values may be due to the reparative effect of oxygen itself. We have observed that some patients receiving TT02 therapy who were clinically stable as a prerequisite for therapy and who had been receiving nasal oxygen therapy for months or years demonstrated increases in arterial oxygen tension after six months that were unrelated to changes in clinical stability or to changes in management of their lung disease. To document these observations, data from our TT02 therapy study were analyzed for changes in arterial oxygen tension after six months of continuous oxygen therapy. We found that 20 percent of our patients would not qualify for oxygen therapy after six months if recertification was required at that time. A retrospective analysis of the data reported by Weitzenblum et al confirmed that 25 percent of their patients, who had been observed for at least one year and had three consecutive ABG measurements performed monthly before oxygen therapy was begun, also would not qualify for oxygen therapy after one year of oxygen therapy because of an increase in Pa02 while breathing ambient air.
Neither of these studies defines how oxygen therapy improves cardiopulmonary function, resulting in an increase in arterial oxygen tension. The Weitzenblum et al study found an overall reduction in Ppa and a trend toward a greater reduction in Ppa in those patients who showed the greatest increases in Pa02.