Role of hypoxemia and pulmonary mechanics in exercise limitation in interstitial lung disease.

We have previously shown that respiratory factors (arterial hypoxemia and/or pulmonary mechanics) contribute to limit maximal incremental exercise in interstitial lung disease (ILD). In this study, we tested the hypothesis that arterial hypoxemia, not pulmonary mechanics, primarily limits maximal exercise in subjects with ILD. Seven subjects with ILD underwent two incremental exercise tests in random order. Test 1: breathing room air (RA); Test 2: breathing 60% O2 with added external dead space (O2VD). Added VD was used to prevent the fall in minute ventilation (VI) while breathing O2. All subjects demonstrated impaired exercise performance (maximal oxygen uptake [VO2], 56 +/- 13% predicted) while breathing RA. There was a significant increase in peak VI (RA, 64.9 +/- 22.3 L/min versus O2VD, 71.0 +/- 20.6; p < 0.05), maximal work rate (RA, 99 +/- 12 watts versus O2VD, 109 +/- 15 watts; p < 0.01), exercise duration (RA, 383 +/- 67 s versus O2VD; 426 +/- 72 s; p < 0.0005) and maximal VO2 (RA, 1.25 +/- 0.21 ...