Characterisation of the unsteady transport of labelled species in permeable capillaries: role of convective dispersion.
A mathematical model of transcapillary exchange has been developed which considers in detail the contribution of Taylor dispersion (i.e., non-uniform velocity and inequalities in radial concentration) to the uptake and wash-out of multiple tracers from single capillaries. A numerical solution to the two-dimensional unsteady-state species continuity equation for a single capillary is obtained (by the use of an array processor) which simulates the convective dispersion of labelled indicators in permeable capillaries. Particular attention is directed toward an analysis of the roles of capillary permeability, transport regime as characterised by the Peclet number, velocity profile and the length of the exchange region on the development of time-concentration profiles and on the importance of convective dispersion. For the physiologic range of parameters consistent with pulmonary capillary transport of multiple indicators (e.g., labelled urea, albumin, etc.), we find that the magnitude of convective dispersion is insufficient to markedly affect the shapes of simulated tracer concentration profiles. The implication in these circumstances is that the use of one-dimensional models, which do not account for Taylor dispersion, does not lead to significant errors in parameter estimates derived from data of multiple indicator dilution.
D002199:Capillary Permeability; D007201:Indicator Dilution Techniques; D008433:Mathematics; D008954:Models, Biological