Low exercise capacity tied to greater ventilatory requirements, dyspnoea in mild COPD

Reduced exercise tolerance in patients with diffusing capacity of the lung for carbon monoxide (DL_CO) less than the lower limit of normal (LLN) is associated with higher ventilatory requirements, a faster rate of decline in dynamic inspiratory reserve volume (IRV), and greater dyspnoea during exercise, suggests a recent study.

“These simple measurements should be considered for the clinical evaluation of unexplained exercise intolerance in individuals with ostensibly mild chronic obstructive pulmonary disease (COPD),” the investigators said.

In this retrospective study, the investigators compared the minute ventilation-to-carbon dioxide output (V˙_E/V˙CO₂), dynamic IRV, dyspnoea, and exercise capacity in groups of patients with Global Initiative for Chronic Obstructive Lung Disease stage 1 COPD with (1) a resting DL_CO at or greater than the LLN (Global Lung Function Initiative reference equations [n=44]) or (2) below the LLN (n=33), and age- and sex-matched healthy controls (n=81).

The two COPD groups had similar spirometry and resting lung volumes. V˙_E/V˙CO₂ (nadir and slope) was consistently greater in the DL_CO < LLN than the other groups during exercise (p<0.05 for all). In addition, the DL_CO < LLN group showed lower IRV and higher dyspnoea intensity at standardized submaximal work rates and lower peak work rate and oxygen intake than the other groups (p<0.05 for all).

“The combination of both reduced resting DL_CO and ventilatory efficiency has been linked to exertional dyspnoea and exercise intolerance in COPD, but the underlying mechanisms are poorly understood,” the investigators noted.