DEAD SPACE LOADING AND EXERCISE LIMITATION IN PATIENTS WITH INTERSTITIAL LUNG-DISEASE

Study design: We tested the hypothesis that maximal exercise performan ce in subjects with interstitial lung disease (ILD) is limited by resp iratory factors. Assuming this is so, ventilatory stimulation by added dead space (VD) should impair exercise capacity. Methods: Six subject s with ILD each underwent three maximal incremental exercise studies o n a bicycle ergometer; control 1, added VD, and control 2. During, the VD study, external VD (500 ml) was added to the circuit, and results obtained were compared with the mean results from the control studies. Results: Exercise duration (TLIM) was significantly less in the VD st udy when compared to the control study (369 +/- 50 vs 439 +/- 55, p < 0.05), as was work rate (102 +/- 13 vs 125 +/- 14 W, p < 0.05) and pea k oxygen uptake per minute (Vo(2)) (1.08 +/- 0.09 vs 1.43 +/- 0.14 L/m in, p < 0.05). At end-exercise, the Borg scale was higher in the VD st udy when compared to the control study (6 +/- 1 vs 5 +/- 1, p < 0.05), while no significant difference in minute ventilation (VI) or oxygen desaturation was noted. When compared to the control study at matched times during exercise, the addition of VD resulted in a significant in crease in VI, while no significant change was noted in Vo(2), carbon d ioxide output (Vco(2)), or heart rate (HR). Conclusion: The decrease o bserved in TLIM, work rate, and peak Vo(2) with added VD, associated w ith a lack of change in VI or oxygen desaturation at end-exercise, sug gests that exercise limitation in ILD isprimarily due to respiratory f actors.