Measurement of continuous distributions of ventilation-perfusion in non-alveolar lungs.

We modified the multiple inert gas elimination technique, which was originally developed for alveolar lungs, to measure continuous distributions of V/Q in the cross-current lungs of birds. In theory, the method is also applicable to counter-current gas exchangers. The algorithms for inferring essentially continuous V/Q distributions from a limited number of measurements and the least-squares approach for dealing with experimental error are independent of the model of gas exchanger being studied. A Monte-Carlo procedure was used to predict the expected frequency of occurrence of given magnitudes of experimental error for each model. If the observed frequency distribution of error exceeds the predicted, then this indicates an incorrect choice of model (analogous to chi-square tests). Thirty-four data sets from 8 geese indicate that: (1) the assumptions of the technique are adequately met; (2) the alveolar model is not appropriate for birds, but the cross-current model is; and therefore; (3) the cross-current modification of the multiple inert gas elimination technique can be used to assess V/Q inequality in avian lungs.