Optimization of Axial Pump Characteristic Dimensions and Induced Hemolysis for Mechanical Circulatory Support Devices

Abstract

The application of axial pumps as ventricular assist devices (VADs) requires significant modifications to the size and characteristics of industrial pumps due to the difference in flow fields of industrial and medical pumps. Industrial pumps operate in the region of Reynolds number Re = 10, whereas axial blood pumps operate in Re < 10. The common pump design technique is to rely on the performance of previously designed pumps using the concept of fluid dynamic similarity. Such data are available for industrial pumps as specific speed-specific diameter (ns-ds) graphs. The difference between the flow fields of industrial and medical pumps makes the industrial ns-ds graphs unsuitable for medical pumps and consequently several clinically available axial blood pumps operate with low efficiencies. In this article, numerical and experimental techniques were used to design 62 axial pump impellers with different design characteristics suitable for VADs and mechanical circulatory support devices (MCSDs). The impellers were manufactured and experimentally tested in various operating conditions of flow, pressure, and rotational speed. The hemocompatibility of the impellers was numerically investigated by modeling shear stress and hemolysis. The highest efficiency of each pump impeller was plotted on an ns-ds diagram. The nondimensional results presented in this article enable preliminary design of efficient and hemocompatible axial flow pumps for VADs and MCSDs.

Hemolytic Performance in Two Generations of the Sputnik Left Ventricular Assist Device: A Combined Numerical and Experimental Study

“…RBP designers mainly face two requirements at this course: highly efficient hydraulic performance and minimization of the impact on blood cells for improved hemocompatibility. Geometric parameters and number of impeller blades [ 28 , 32 , 33 , 34 , 35 , 36 , 37 , 39 ], size of clearance gap between impeller blades and flow path housing [ 28 , 29 , 38 ], distance between trailing edge of impeller blades and leading edge of diffuser blades, clearance gap between diffuser blades and impeller central hub [ 27 , 29 , 31 ], and number of diffuser blades [ 30 , 31 ] were shown to be design parameters influencing the hydraulic efficiency and the predictions of blood damage. These parameters were studied for different basic designs of both axial and centrifugal RBPs with the only one parameter varied and others fixed.…”

“…When the fluid accelerated by the impeller runs on stationary blades of the diffuser, kinetic energy is converted into potential pressure energy, while the direction of flow is aligned along the central axis of flow path. In general, occurrence and amount of hemolysis are influenced by various changes in geometric parameters of flow path [ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ], for example, by changes in size of clearance gap between impeller blades and flow path housing. Smaller gaps induce increased values of shear stress, and larger gaps induce lesser values of shear stress, but increase the exposure time due to appearance of leakages, back flows and recirculation zones [ 27 , 28 , 29 , 38 ].…”

Haemolysis induced by mechanical circulatory support devices: unsolved problems

“…The critical haemolysis level of this impeller configuration is only exceeded at speeds above 7,000 L/min. 2 Corresponding investigations in centrifugal pumps show that these have a considerably higher efficiency than axial pumps. The most favourable outlet angle of the impeller blades for these pumps is either 15° or 30°.…”

“…In a healthy person, the concentration of free haemoglobin in blood caused by natural haemolysis is about 0.5-2.0 mg/100 L. A level of 10 mg/100 L is currently assumed to be tolerable for humans. 1,2 If the damage level of RBCs is higher, the production rate of new RBCs cannot substitute the losses. Premature erythrocyte loss can be caused by unnatural haemolysis as a result of increased mechanical stress on the RBC, resulting in increased permeability of the cell membrane for haemoglobin or rupturing of the cell membrane.…”

The Discrete-Continuous, Global Optimisation of an Axial Flow Blood Pump

“…Frazier et al [12] modified an existing axial-flow pump by increasing its inducer-impeller inlet angle hence increasing its pressure responsivity. Korakianitis et al [13] tested the performance of sixty two axial pump impellers with varying outlet angles and number of blades, i.e. only two design variables.…”