Flexible Impeller Blades in an Axial Flow Pump for Intravascular Cavopulmonary Assistance of the Fontan Physiology

Abstract

An intravascular axial flow blood pump has suitable hydraulic characteristics for use to augment pressure in the cavopulmonary circulation in Fontan patients. This study presents the experimental hydraulic performance testing of six flexible-bladed and one rigid-bladed pump prototypes for mechanical cavopulmonary assist. Unique in design, six of these prototypes were manufactured using varying grades of polyurethane material to reduce blade hardness. The hydraulic performance of these prototypes were measured and quantitatively compared to a rigid-bladed prototype through a regression analysis. To shield the vessel wall from the rotating impeller blades, two novel protective cage designs were also evaluated for additional energy augmentation. The pumps with no protective cage produced pressure rises of 1-12 mmHg for flow rates of 0.5-4 L/min at rotational speeds of 4000-7000 rpm. The flexible-bladed prototypes generated pressure rises within 12% of the rigidbladed pump design. The most flexible prototype (F-15) was able to generate pressure rises within 4.1% of the rigidbladed impeller. The partially twisted and fully twisted protective cage designs also functioned as desired by augmenting energy transfer in range of 5-15 mmHg, respectively. This study dispels the assumption that rigid-impeller blades are absolutely necessary to maintain the pressure generation of rotary blood pumps and demonstrates the potential of uniquely shaped cage filaments to augment the energy transfer of an axial flow blood pump for mechanical cavopulmonary assistance. The successful development of this blood pump will provide clinicians with a therapeutic option for mechanically supporting the failing Fontan physiology in adolescent and adult patients.

Pressure–Flow Experimental Performance of New Intravascular Blood Pump Designs for Fontan Patients

“…As a comparison technique, we performed a nondimensional regression analysis of the pressure–flow performance data for each individual impeller prototype . This procedure has been used extensively in the assessment of earlier pump designs . The discrete data points for pressure and flow were condensed into two nondimensional coefficients for each prototype tested for the rotational speeds evaluated.…”

Design of Axial Blood Pumps for Patients With Dysfunctional Fontan Physiology: Computational Studies and Performance Testing

“…In an effort to quantitatively compare the performance data, we carried out a nondimensional regression analysis on the pressure and flow data in order to compare the overall performance between the impeller prototypes (7,15). This procedure has been previously developed (7,16,17). The individual discrete data points for pressure and flow are consolidated into two nondimensional coefficients for each prototype tested.…”

Design Method of a Foldable Ventricular Assist Device for Minimally Invasive Implantation

“…These foldable impellers can be achieved by mechanical and/or material means (5)(6)(7). Mechanically folded structures adapt joints and links to facilitate the folding process, whereas utilization of elastic materials allows the structure to be bent or twisted without permanent deformation.…”

“…However, the elastic materials are generally insufficient to withstand the hydrodynamic loads during operation, resulting in an impaired pump efficiency (7). A nonlinear material can exhibit a high, linear elastic modulus at small operational loads and a lower elastic modulus at high stress such that large, recoverable strains can be achieved during folding.…”

“…Nevertheless, a blade should always be optimized for sufficient output and optimal hemodynamic performance. This optimization can lead to a highly curved blade geometry that makes it challenging to fold without compromising the hydraulic efficiency (7,8). Once a blade design for a foldable device is confirmed, it is then critical to investigate its foldability by evaluating the resulting stress and strain during operating and folded states.…”