An analysis of sequential physiologic changes in hypoxic cor pulmonale during long-term oxygen therapy.

Physiologic changes were studied retrospectively in 37 patients with hypoxic cor pulmonale who died during long-term oxygen therapy (LTOT). The subjects were assessed during periods of clinical stability for each year on LTOT. At the onset of treatment, their mean age (+/- SEM) was 60.0 +/- 1.3 years, and at the time of death, they were aged 65.0 +/- 1.3 years. The median duration of LTOT was five years. For each year leading up to death, mean values of FEV1, PaO2, and PaCO2 were obtained. A rate of decline of FEV1 of 73 +/- 10 ml/yr was observed, and this was accompanied by a decline in PaO2 of 0.47 +/- 0.01 kPa/yr. Patients died with a mean FEV1 of 0.55 +/- 0.04 L and a PaO2 of 5.1 +/- 0.2 kPa. A small rise in PaCO2 occurred, on average 0.25 +/- 0.09 kPa/yr, throughout the study, but accelerating in many cases during the three years before death. Hypoxic cor pulmonale appears to be associated with a rapid deterioration in airway function, a steady decline in PaO2, and a slow rise in PaCO2 during the years leading up to death. These physiologic changes measured in a stable clinical state while breathing air appear to occur in spite of LTOT. The LTOT may merely prevent death from episodes of severe hypoxemia while the pathophysiologic changes in the lung progress. Hence the benefit to be expected from LTOT is only temporary. Generally, those patients with lower levels of FEV1 will obtain diminishing clinical benefit, inversely related to the severity of airflow obstruction at the time of commencement of LTOT.