Effect of alveolar volume and sequential filling on the diffusing capacityof the lungs: II. Experiment

The diffusing capacity of the lung, DL, is a critical physiological paramet er, yet the currently accepted clinical model (Jones-Meade) assumes a well- mixed alveolar region, and a constant DL independent of alveolar volume, VA , despite experimental evidence to the contrary. We have formulated a new m athematical model [Tsoukias, N.M, Wilson, A.F., George, S.C., 2000. Respir. Physiol 120, 231-249] that considers variable alveolar mixing through a si ngle parameter, k (0 < k < 1), and a DL that is a positive function of VA ( DL = a + bVA or DL = alpha VA(beta)). The goal of this study is to determin e the suitability of this model to determine the unknown parameters a: b, a lpha, beta, and k from experimental data in normal subjects. The model pred icts that the normal lung fills, in part, sequentially (k = 0.51 +/- 0.35). The following average values in all seven subjects were obtained: DLNo=48. VA(2/3) ml/min/mmHg and DLCO = 20 + 0.7.VA ml/min/mmHg (STPD) where VA is e xpressed in L (STPD). We conclude that the mathematical model is suitable f or identifying the unknown parameters and thus can be used to characterize the degree of alveolar mixing (or sequential filling) as well as the volume dependence of Dr. (C) 2000 Elsevier Science B.V. All rights reserved.