Identification of cardiac afterload dynamics from data

The prospect of ex vivo functional evaluation of donor hearts is considered. Particularly, the dynamics of a synthetic cardiac afterload model are compared to those of normal physiology. A method for identification of continuous-time transfer functions from sampled data is developed and verified against results from the literature. The method relies on exact gradients and Hessians obtained through automatic differentiation. This also enables straightforward sensitivity analyses. Such analyses reveal that the 4-element Windkessel model is not practically identifiable from representative data while the 3-element model underfits the data. Direct comparison of aortic pressure-flow relations, without relying on matching of fitted Windkessel model parameters, is therefore suggested as an alternative for comparing afterload dynamics. Copyright (C) 2021 The Authors.