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 iden tify possible predictive factors, we compared dyspnea at rest (baseline) an d during exercise in 27 patients with chronic obstructive pulmonary disease (COPD) and 39 pulmonary fibrosis (PF) patients. We also compared spirometr y and blood gases at rest and after exercise, which consisted of a 12-minut e walking test (12WT). Heart rate and oxygen saturation (SaO(2)) were recor ded every two minutes during the 12WT. Distance walked was also recorded. A lthough dyspnea changed during the 12WT in both groups (p<0.001), the maxim um level of dyspnea reached in the two groups was not statistically differe nt. COPD patients walked farther than did PF patients (782 <plus/minus>182 in vs. 618 +/- 225 in, respectively; p=0.002) and paused less often during the 12WT 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, distan ce walked and pauses during the 12WT, we found that only SaO(2) was signifi cantly related to severity of dyspnea during exercise. We conclude that the re are important differences in degree of dyspnea experienced during exerci se by COPD and PF patients and that SaO(2) is the only variable that predic ts severity of dyspnea.