Describing function approximation for biomedical engineering applications

The paper focuses on the determination of suitable approximations for sigmoid-type nonlinear characteristics, which are common to physiological systems, particularly cardiovascular regulatory systems. These sigmoid nonlinearities have been implicated in the development of limit cycle oscillations in blood pressure. Approximations of the sigmoid are required since the describing function is not calculable for all the representations of the sigmoid characteristic. We present a new approximation, which gives a better overall approximation of the sigmoid and, hence, can assist the use of describing functions in the diagnostic analysis of cardiovascular function.