Mechanisms of Exertional Dyspnea in Patients with Mild COPD and a Low Resting DLCO.

Abstract

Patients with mild chronic obstructive pulmonary disease (COPD) and lower resting diffusing capacity for carbon monoxide (DL_CO) often report troublesome dyspnea during exercise although the mechanisms are not clear. We postulated that in such individuals, exertional dyspnea is linked to relatively high inspiratory neural drive (IND) due, in part, to the effects of reduced ventilatory efficiency. This cross-sectional study included 28 patients with GOLD I COPD stratified into two groups with (n = 15) and without (n = 13) DL_CO less than the lower limit of normal (2 (V̇_E/V̇CO₂), and respiratory mechanics during incremental cycle exercise in the three groups. Spirometry and resting lung volumes were similar between COPD groups. During exercise, dyspnea, IND and V̇_E/V̇CO₂ were higher at equivalent work rates (WR) in the DL_COp < 0.05). In patients with DL_COp < 0.05). The dyspnea/IND relationship was similar across groups; therefore, the increased dyspnea at a standardized WR in the low DL_COCOV̇_E/V̇CO₂ at a given work rate. Higher ventilatory requirements in the DL_CO