Determinant factors of pulmonary function and respiratory muscle strength on exertional dyspnea in patients with chronic obstructive pulmonary disease (COPD)

The effects of pulmonary function and respiratory muscle strength on exertional dyspnea in patients with chronic obstructive pulmonary disease (COPD) have not been fully elucidated. We examined the relationships between pulmonary function, static respiratory pressure, and dyspneic sensation during exercise in 48 patients with COPD. Dyspneic sensation during exercise was quantitated by a Borg scale slope (BSS, BS/VO2) and the threshold load of dyspnea (TLD). BSS was negatively correlated with VC, FEV1, V 25, RV/TLC (%). DLCO and PImax, whereas TLD was positively correlated with VC, FEV1, V 25, FRC and RV/TLC. Linear regression analysis revealed that FEV 1 and FRC were independent predictors for TLD, and that RV/TLC (%) was an independent predictor for BSS. These results suggest that an increase of air trapping as indicated by RV/TLC may be a major factor contributing to both decreased TLD and increased BSS, resulting in an increased sensation of dyspnea during exercise in patients with COPD.