Changes in pulmonary gas exchange in chronic obstructive bronchopneumopathies and their modifications induced by therapy

In order to assess the mechanisms of gas exchange disturbances (i.e. to what extent shunting and diffusion impairment contribute to hypoxemia) in chronic obstructive pulmonary disease (COPD) and respiratory failure, ventilation-perfusion relationships (V/Q) by the multiple inert gas elimination technique were obtained in 16 patients with respiratory failure breakthrough. In 6 instances the study was repeated after long-term treatment with the aim to analyze V/Q changes after therapy. Initially, patients showed severe hypoxemia and hypercapnia and they presented signs of marked bronchoconstriction. A great dispersion of V and Q distribution was present as indicated by the marked increase of the second moment of V and Q distributions. Interestingly, few patients presented a unimodal distribution of both V and Q, whereas most-patients had bimodal distributions where the ventilation was distributed in a mode such that high V/Q areas were present between 10 and 100 of V/Q ratio and blood flow was displaced leftward or toward lower V/Q values. No correlations were found between V and Q distribution and clinical types A or B of COPD. Significant relationships were found between measured and calculated arterial PO2 (r = 0.90, p less than 0.001) and between measured PO2 and the sum of the fractional perfusion to regions with V/Q ratio less than 0.1, suggesting that V/Q inequality and shunting, instead of the impairment of diffusion equilibration, can account for all the hypoxemia. Finally, the reduced inhomogeneity of ventilation after treatment, especially in the fraction located in high V/Q regions is mostly related to some functional and reversible damages in COPD.