Simulation of Gas Transport in an Intravenacaval Blood-Gas Exchange device (IVOX)©

Abstract

A mathematical model of a novel intravascular hollow-fiber gas exchange device, called IVOX©, is developed using a Krogh cylinderlike approach wherein a unit structure is assumed to comprise of a single fiber with gas flowing through its lumen and surrounded by another coaxial cylinder of blood flowing in the opposite direction. Species mass balances on O2 and CO2 result in a nonlinear coupled set of convective-difTusion parabolic partial differential equations that are solved numerically using an alternating direction implicit finite-difference method. Computed results indicate the presence of a large resistance to gas transport on the external (blood) side of the hollow fiber exchanger. Increasing gas flow through the device was found to favor CO2 removal but not O2 addition to blood. On the other hand, increasing blood flow over the device favored both CO2 removal as well as O2 addition. Neglecting the vacuum pressure gradient on the gas side results in an underestimate of CO2 transport but an overestimate of O2 transport. The exchange rates of CO2 and O2 were found to increase directly with the transmural Pco2 gradient imposed across the device. This strongly suggests that CO2 removal may be enhanced in a clinical setting under conditions of permissive hypercapnia (controlling respiratory acidosis by bicarbonate infusion). Fiber crimping was studied indirectly; improved blood mixing produced by the crimped fibers was mimicked by increasing species diffusivity in blood. The resulting lowered blood-side resistance favored species transfer.