Abstracts From the 17thCongress of the ISRBP

Abstract

Objective: The preload sensitivity of a RBP is an important feature for a device to alter outflow in response to changing patient physiologic conditions, as per the Frank-Starling response of the natural heart. Since RBP’s are pre/afterload dependant, a constant afterload and RPM could result in a change in outflow with a change in preload, with the gradient determining the inherent preload sensitivity. This study investigated the preload vs outflow gradient of a number of RBP types to determine which has the greatest preload sensitivity, and compared it to that of the natural heart. Method: An in-vitro mock circulation loop was used to record the change in outflow from a centrifugal, mixed flow, and axial flow rotary blood pump while varying LA preload values and keeping either afterload, or downstream peripheral resistance constant. Each pump was initially configured to produce haemodynamics of 100mmHg and 5L/min, with a LAP of 10mmHg. While maintaining pump speed and an afterload of 100mmHg, LAP was varied by +/-10mmHg, and resulting outflow recorded. Result: The centrifugal pump with straight vanes exhibited the greatest preload sensitivity; with the highest gradient of ?Q vs ?P recorded (0.22 l/min/mmHg) while maintaining constant afterload of 100mmHg. This gradient increased as flow rates reduced, and decreased as flows increased above design conditions. The mixed flow (0.18 l/min/mmHg), and axial flow pump (0.07 l/min/mmHg) both maintained unchanging gradients for all flow rates. Conclusion: The PQ characteristic curve of the RBP influences the preload sensitivity. A flatter P-Q curve increased the gradient of ?Q to ?Pin and thus preload sensitivity, which was emphasised during flow rates below the design point of the device. However, these did not match the gradient of the natural left heart at the design point. Therefore some form of speed control should be included to increase sensitivity to preload changes.