In vivo validation of pulsatile flow and differential pressure estimation models in a left ventricular assist device.

Implantation of sensors to measure hemodynamic parameters such as pulsatile pump flow and differential pressure (head) in an implantable rotary pump (IRBP) requires regular in situ calibration due to measurement drift. In addition, risks associated with sensor failure and thrombus formation makes the long-term implantation in patients problematic. In our laboratory, two stable and novel dynamical models for non-invasive pulsatile flow and head estimation were proposed and tested in vitro using mock circulatory loop experiments with varying hematocrit (HCT). Noninvasive measurements of power and pump speed were used as inputs to the flow model while the estimated flow was used together with the pump rotational speed as inputs to the head estimation model. In this paper, we evaluated the performance of the proposed models using in vivo experimental data obtained from greyhound dogs (N=5). Linear regression analysis between estimated and measured pulsatile flows resulted in a highly significant correlation (R(2) = 0.946) and mean absolute error (e) of 0.810 L/min, while for head, R(2) = 0.951 and e = 10.13 mmHg were obtained.