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

Morphologic changes in pulmonary muscular arteries may modify the mechanisms that regulate the pulmonary vascular tone and contribute to maintaining an adequate ventilation-perfusion (VA/Q) matching in patients with chronic obstructive pulmonary disease (COPD). To analyze the relationships between the abnormalities of pulmonary muscular arteries and the degree of VA/Q inequality, and to assess the effect of these abnormalities on the changes in VA/Q relationships induced by oxygen breathing, we studied a group of patients with mild COPD undergoing resective lung surgery. According to the degree of airflow obstruction and the increase in VA/Q mismatch produced by 100% O-2, breathing (Delta logSD Q), patients were divided into three groups: (A) patients with normal lung function, (B) patients with airflow obstruction and a high response to oxygen (Delta logSD Q > 0.4), and (C) patients with airflow obstruction and a low response to oxygen (Delta logSD Q < 0.4). Pulmonary arteries in Groups B and C showed narrower lumens and thicker walls than in Group A, These morphologic changes were produced mainly by an 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 artery diameter showed that the increase in intima in Group C took place predominantly in arteries with small diameters (< 500 mu m). The mean intimal 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 with a higher degree of VA/Q inequality, and that intimal thickening in small arteries seems to reduce the response of the pulmonary circulation to different oxygen concentrations.