Fluid-structure Interaction Analysis of Implantable Axial Flow Blood Pump Impeller for Fontan Patients

摘要

Infants who are born with cardiac defects that are characterized as a single ventricle physiology face numerous physiological complications, such as early-onset congestive heart failure, thrombosis, arrhythmias, and protein losing enteropathy. Clinical treatment and management costs for this cohort of patients exceed $1 billion/year. It is theorized a systemic pressure boost of 1-5mmHg is sufficient to alleviate many of these complications, and there is a growing interest in the use of blood pumps as a bridge therapy to heart transplantation. Currently available blood pumps have limited use in these patients because they are large and designed for adults. A major constraint of current pumps is the diameter, rigid fixed-blade designs and off-design operation due to the rigid designs, which leads to irregular flow patterns, inefficient performance, and blood damage. The presented study investigates the use of flexible blade designs to begin working toward the design of a minimally invasive blood pump with blade pitch adjusting capabilities. Using one-way fluid-structure interaction (FSI) computational studies, the implications of blade deformation on pump performance and blood damage was investigated for flexible impellers made from biocompatible materials such as nitinol, polyurethane, and silicone. It was found that rotational speed is the largest determinant of impeller deformation and the maximum deformation occurred at the blade trailing edge. The models predicted the maximum impeller deformation for nitinol to be 40nm, Bionate 80A polyurethane to be 106um, and silicone to be 2.8 mm, all occurring at 9000 RPM from 15 kPa of fluid pressure on the trailing edge of the impeller blade. The effects of silicone deformation on pump performance was significant, particularly at rotational speeds above 5000 RPM where a decrease in pressure generation of more than 10% was observed for all rotational speeds. Despite the loss, pressure generation still exceeded the level required to alleviate Fontan complications and with proper characterization the loss could be overcome through optimization of operating conditions. The estimated blood damage observed for all materials tested at all operational conditions remained below a level acceptable for blood pumps. The contributing effect of significant impeller deformation on blood damage was inconsistent and requires additional investigation because deformation did reduce blood damage metrics in some circumstances, something that could be leveraged in the future with further study. These results support the continued development of an axial-flow, mechanical assist device as a new clinical therapeutic option for patients with dysfunctional or failing single ventricle physiology.