[Severity of dyspnea during exercise: similarities and differences between patients with COPD or pulmonary fibrosis]

To understand the mechanisms leading to dyspnea during exercise and to identify possible predictive factors, we compared dyspnea at rest (baseline)and during exercise in 27 patients with chronic obstructive pulmonary disease (COPD) and 39 pulmonary fibrosis (PF) patients. We also compared spirometry and blood gases at rest and after exercise,which consisted of a 12-minute walking test (12 WT). Heart rate and oxygen saturation (SaO2) were recorded every two minutes during the 12 WT. Distance walked was also recorded. Although dyspnea changed during the 12 WT in both groups (p < 0.001),the maximum level of dyspnea reached in the two groups was not statistically different. COPD patients walked farther than did PF patients (782 +/- 182 m vs. 618 +/- 225 m, respectively;p = 0.002) and paused less often during the 12 WT than did PF patients(0.18 +/- 0.55 vs. 0.82 +/- 1.55, respectively; p <0.05). After adjusting for diagnosis, age, sex, baseline dyspnea,distance walked and pauses during the 12 WT, we found that only SaO2 was significantly related to severity of dyspnea during exercise. We conclude that there are important differences in degree of dyspnea experienced during exercise by COPD and PF patients and that SaO2 is the only variable that predicts severity of dyspnea.