PULMONARY VASCULAR ABNORMALITIES AND VENTILATION-PERFUSION RELATIONSHIPS IN MILD CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

Morphologic changes in pulmonary muscular arteries may modify the mech anisms that regulate the pulmonary vascular tone and contribute to mai ntaining an adequate ventilation-perfusion (VA/Q) matching in patients with chronic obstructive pulmonary disease (COPD). To analyze the rel ationships between the abnormalities of pulmonary muscular arteries an d the degree of VA/Q inequality, and to assess the effect of these abn ormalities on the changes in VA/Q relationships induced by oxygen brea thing, we studied a group of patients with mild COPD undergoing resect ive lung surgery. According to the degree of airflow obstruction and t he increase in VA/Q mismatch produced by 100% O-2, breathing (Delta lo gSD Q), patients were divided into three groups: (A) patients with nor mal lung function, (B) patients with airflow obstruction and a high re sponse to oxygen (Delta logSD Q > 0.4), and (C) patients with airflow obstruction and a low response to oxygen (Delta logSD Q < 0.4). Pulmon ary arteries in Groups B and C showed narrower lumens and thicker wall s than in Group A, These morphologic changes were produced mainly by a n enlargement of the intimal layer and were more pronounced in Group C than in Group B. The assessment of intimal area as a function of arte ry diameter showed that the increase in intima in Group C took place p redominantly in arteries with small diameters (< 500 mu m). The mean i ntimal area on each subject correlated with both the Pa-O2 value (r = -0.46, p < 0.05) and the overall index of VA/Q mismatching (r = 0.51, p < 0.05). We conclude that in patients with mild COPD the enlargement of the intimal layer in pulmonary muscular arteries is associated wit h a higher degree of VA/Q inequality, and that intimal thickening in s mall arteries seems to reduce the response of the pulmonary circulatio n to different oxygen concentrations.