Measurements of differential diffusion in a liquid-filled lung model

 A noninvasive method for obtaining quantitative images of differential diffusion in liquid-filled lung models is presented. The method utilizes planar fluorescence imaging to obtain differences in concentration fields and was tested on an oscillatory flow of water in a Y-shaped tube. Differences as large as 36% were measured between the concentration fields of two dyes having a factor of 15 difference in their diffusion coefficient. The method is applicable to the study of differential diffusion in any internal flow. The relevance to recent clinical studies of liquid phase respiration (Greenspan et al. 1990) is discussed. Received: 6 September 1996/Accepted: 7 April 1997