Gas Exchange during Exercise in Mild Chronic Obstructive Pulmonary Disease: Correlation with Lung Structure

Abstract

To investigate whether or not the pathologic features in the lungs of patients with chronic obstructive pulmonary disease (COPD) are related to the gas exchange response during exercise, we studied 17 patients (15 men, two women) with mild-to-moderate airflow obstruction (FEV₁/FVC ratio, 59 ± 3%) undergoing resective lung surgery, at rest and during submaximal exercise (71 ± 5% predicted o₂max). During exercise, arterial Po₂ increased (from 81 ± 3 to 86 ± 3 mm Hg, p < 0.05) as a result of an overall improvement in a/ relationships. This improvement included an increase in the mean a/ ratios of both ventilation and blood flow distributions, and a more homogeneous ventilation distribution (logSD V, from 0.66 ± 0.06 to 0.50 ± 0.03; p < 0.01; normal value, ⩽ 0.6). The morphologic evaluation of the resected specimens disclosed a moderate degree of emphysema (emphysema score, 16 ± 4) and mild abnormalities in membranous bronchioles (total pathology score, 107 ± 8). At rest, significant correlations were found between the severity of the pathologic findings and both the degree of hypoxemia and the extent of a/ mismatching. During exercise, no relationship between branchiolar abnormalities and gas exchange measurements was observed, whereas the severity of emphysema was correlated with Pa_{O2 (r = −0.54, p < 0.05). Both the overall increase in and the more efficient distribution of ventilation accounted for the improvement in a/ distributions during exercise. These changes were more pronounced in patients with a greater degree of bronchiolar abnormalities. We conclude that in patients with mild COPD, neither emphysema nor bronchiolar abnormalities preclude an adequate adaptation of ventilation that results in the improvement of gas exchange during exercise.}