Le alterazioni degli scambi gassosi polmonari nelle broncopneumopatie croniche ostruttive e loro modificazioni indotte dalla terapia

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 relationshìps (V/Q) by the multiple inert gas elimination technique were obtained in 16 patients with respiratory failure breakthrough. In 6 istances the study was repeated after long-term treatment with the aim to anaIyze V/Q changes after therapy. Initially, patients showed severe hypoxemia and hypercapnia and they presented signs of markedbronchoconstriction. 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 pa- tients had bimodal distributions where the ventilation was distributed in a mode such that high V/Q areas were present between IO and lDOof V/Q ratio and biood fiow 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 P02 (r = 0.90, p < 0.001) and between measured P02 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 impairrnent of diffusion equilibration, can account for all the hypo- xemia. Finally, the reduced inhomogeneity of ventilation after treatment, expecially in the fraction located in high V Q regions is mostly related to some functional and reversible damages in