Variations of ventilation and diffusing capacity to perfusion determining the alveolar-arterial O₂ difference: theory

The factors determining the alveolar-arterial O 2 pressure difference, AaD, have been theoretically reinvestigated, taking into account the effect of unequal distribution of pulmonary diffusing capacity, D, to pulmonary perfusion, Q. It is shown that, for a given inspired gas and a given mixed venous blood, the AaD is determined by two parameters, the ratios diffusing capacity :perfusion, D/Q, and alveolar ventilation :perfusion, Va/Q. Two characteristics of both of these ratios, the mean value and the variation, affect the AaD. Submitted on May 23, 1960