Evolution of Physiological Variables in Patients with Chronic Obstructive Pulmonary Disease before and during Long-Term Oxygen Therapy

In 24 patients with severe chronic obstructive pulmonary disease (COPD), we investigated the evolution of pulmonary volumes, arterial blood gases (ABG) and mean pulmonary artery pressure (PAP), before (T₀-T₁) and during (T₁-T₂) long-term oxygen therapy (LTO). LTO was initiated at T₁ on usual criteria (PaO₂ persistently ≤55 mm Hg) and was given during ≥16 h/day. The T₀-T₁ period ranged from 12 to 186 months (mean 53 ± 41 months) and the T₁-T₂ period from 12 to 120 months (mean 44 ± 30 months). There was a significant worsening of the obstructive pattern (FEV₁ decreasing from 1,084 ± 326 to 879 ± 318 ml, p < 0.005) and of ABG (PaO₂ decreasing from 58.2 ± 9.2 to 51.6 ± 6.5 mm Hg, p < 0.01) before the onset of LTO, whereas there was a rather good stability of ABG during LTO and the changes in pulmonary volumes were modest and statistically nonsignificant (FEV₁ decreased from 879 ± 318 to 809 ± 247 ml). PAP tended to increase from T₀ to T₁ and to decrease from T₁ to T₂, but these changes only reached the level of statistical significance when they were expressed as changes per year ( + 1.0 ± 2.7 vs. –1.3 ± 4.5 mm Hg, p < 0.05). The evolution of physiological variables was nearly identical in subgroups of patients who had died (n = 13) or were still alive (n = 11) at the time of data collection (T₃) and this held particularly true for PAP. However, FΕV₁ at T₂ was significantly lower (p < 0.01) in patients who died. It is concluded that the progressive deterioration of pulmonary volumes, ABG and PAP, which is observed before the onset of LTO is reduced (lung volumes), stopped (ABG) or reversed (PAP) during LTO. In COPD patients under LTO, prognosis is not related to the evolution of PAP or ABG (in ambient air) but rather to the worsening of bronchial obstruction