Computer simulations of oxygen transport by hemoglobin solutions with differing oxygen affinities in arteriolar‐sized, artificial vessels

Abstract

Oxygen transport in blood flowing through an arteriole is characterized by an immobile hemoglobin (Hb) phase contained within erythrocytes and a plasma phase through which dissolved O2 must diffuse to reach tissue. The dissolved O2 gradients drive lateral O2 transport, and the amount of O2 in plasma is much smaller than the O2 bound to Hb within red cells. Acellular Hb solutions, designed to subsidize O2 supply during blood loss, have a variety of equilibrium O2 binding properties and molecular diffusivities that are 5 50 times smaller than that of dissolved O2. Since acellular Hbs are used at concentrations 10–100 times larger than local dissolved O2 concentrations, lateral O2 transport is “facilitated” due to outward diffusion of oxyhemoglobin. Simulations of O2 delivery in arteriolar-sized, gas permeable tubes were performed for different Hb solutions to quantify the effect of facilitated diffusion by integrating radial HbO2 fluxes. At a given [Hb], cell-free Hbs deliver O2 in a qualitatively different manner than an erythrocyte suspension at the same intracellular [Hb]. Hbs with low O2 affinities (P50>16 mmHg) and larger diffusivities (D=10−6 cm2/s) offload O2 faster than blood at the same [Hb]. There is a small difference in O2 offloading for Hbs with P50=16 or 33 mmHg. Hbs with higher oxygen affinity (P50<10 mmHg) and smaller diffusivity (D=10−7 cm2/s) release O2 slower than blood at the same [Hb]. The delivery of O2 for a mixture containing high-O2 affinity, small-diffusivity Hb and red cells is qualitatively similar to that of red cells alone.