ENGINEERING ANALYSIS OF TWO BLOOD TRANSPORT PROBLEMS: I. OSCILLATORY AND PULSATILE FLOW OF BLOOD IN SMALL GLASS TUBES. II. OXYGEN TRANSPORT IN A RED BLOOD CELL

Engineering analysis is applied to two problems: (1) an experimental study of time-dependent blood flow and (2) a theoretical study of oxygen (O(,2)) transport in a red blood cell (RBC). Since in vivo blood flow is time-dependent, the ability to predict unsteady blood flow from steady-flow rheological data for blood is of interest. Oscillatory and pulsatile flow of blood and related suspensions was studied in 400 (mu)m and 218 (mu)m glass tubes at 37(DEGREES)C. The flow was sinusoidally driven with a frequency of 0.5 Hz to 3.0 Hz, and the resulting pressure gradient in the tube was measured. The pressure and flow data were compared to a predicted relation obtained from solving the momentum equation subject to rheological data; these data were acquired from steady-flow viscometers at a hematocrit (RBC concentration) value equal to the average tube hematocrit. For a given pressure-gradient amplitude for oscillatory flow, the predicted flowrate amplitude is smaller than that found by experiment. The discrepancy is attributable to a residual Fahraeus-Lindqvist effect not compensated for by using the average tube hematocrit in the predictions. In addition, the discrepancy depends on the RBC suspending medium and the hematocrit, and is less than about 10 percent for RBC in plasma. Pulsatile flow was more predictable than oscillatory flow, indicating possible differences in the Fahraeus-Lindqvist effect for the two cases. Viscoelastic fluid effects were negligible. The second problem deals with O(,2) transport in a red cell. A significant fraction of intracapillary resistance to O(,2) transport occurs in the red cell and is not well understood. A simple model is used to study the interaction of diffusion, facilitated diffusion, and reaction kinetics during the O(,2) unloading of a red cell. The nonequilibrium region adjacent to the RBC membrane is elucidated using boundary layer analysis, and the O(,2) transport equations are solved numerically using double orthogonal collocation. The minimum time required to unload O(,2) from a red cell is calculated and depends strongly on the plasma surrounding the cell. The minimum release time is comparable to some estimates of capillary transit time in working skeletal muscle. The present model is compared to the standard Krogh model for O(,2) transport