Blood flow and gas transport at the fiber level in an artificial lung.

Time-dependent blood flow and gas transport in an artificial lung are investigated to understand the influence of factors related to device design and operation. Maximum gas transport efficiency, minimum device pressure drop (a measure of resistance), and small local shear stresses (a measure of potential blood cell trauma) are desired. The artificial lung is computationally modeled at the fiber level as a single cylinder and cylinder arrays. Blood is pumped into the device by the right ventricle, in some instances passing through a compliance chamber first. The flow leaving the compliance chamber is modeled as pulsatile, consisting of a sinusoidal perturbation superimposed on steady flow. The right ventricular flow is modeled to depict the rapid flow acceleration and then deceleration during systole followed by zero flow during diastole. Both a Newtonian fluid and blood modeled as a Casson fluid coupled with the hemoglobin gas binding properties are considered. Oxygenation experiments to water for a fiber bundle are investigated for steady and right ventricular flow. It was computationally observed that pulsatile flow yielded slightly smaller gas transport than steady flow, while right ventricular flow (studied for the cylinder array) resulted in markedly smaller gas transport, with the difference increasing with Reynolds number, Re. The experiments yielded similar qualitative results. The maximum pressure drop across the cylinder array (or similarly single cylinder drag force) and the maximum shear stress are lowest for steady flow, increasing for pulsatile flow, and increasing greatly for right ventricular flow while the average pressure drop and shear stress are nearly equivalent for all three flow types. The Sherwood number, pressure drop, and shear stress increase with Re and, for a cylinder array (as investigated for blood), decreasing porosity and AR > 1 (AR = aspect ratio). In general, for any fiber array geometry or likewise for a single cylinder, high (low) Sherwood numbers correlate with high (low) pressure drop and shear stresses creating a need for a compromise. Specifically, device porosity, aspect ratio, and operating Re must be carefully selected. In addition, dampening artificial lung inlet flow is expected to improve performance.Ph.D.Applied SciencesBiomedical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126609/2/3253560.pd