An analog computer analysis of regional diffusing capacity in airflow obstruction

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Abstract
Fifteen subjects with airflow obstruction rebreathed a mixture of Ne, CO, and C2H2 in air for 30-45 sec. Five samples were taken from the rebreathing bag on inspiration and the changes of Ne and CO concentration with time in these subjects were analyzed in terms of a two- or three-region electrical analog of the lung by altering the parameters of the model to duplicate, successively, neon mixing and CO absorbtion of each patient. Values thus obtained show that regional diffusing capacity is apparently proportional to regional volume and clearly not proportional to regional ventilation. Because of two-compartment lung oversimplifies nature, because the model cannot deal with stratified inhomogeneity or sequential ventilation without distorting regional volume and ventilation, because diffusing regions may not coincide with ventilating regions, and because CO concentration is insensitive to changes in diffusing capacity in very poorly ventilated regions, proportionality of diffusing capacity to lung volume is not established. Total diffusing capacity can be measured by rebreathing when uneven ventilation is moderate, but not when sever.