Motivated by a problem from pharmacology, we consider a general two parameter slow-fast system in which the critical set consists of a one dimensional manifold and a two dimensional manifold, intersecting transversally at the origin. Using geometric desingularisation, we show that for a subset of the parameter set there is an exchange of stabilities between the attracting components of the critical set and the direction of the continuation can be expressed in terms of the parameters.
MotivationWe consider the pharmacological model of dimerisation where a receptor binds to two ligand molecules. The dimerisation model is an adaptation of the well studied target mediated drug disposition model (TMDD) in which the receptor binds to one ligand molecule, see [5] for more details. In both models, it is assumed that the binding is the fastest process. This gives a separation of time scales, which allows us to use geometric singular perturbation theory to analyse these models. For the TMDD model, the critical set reduces to two intersecting one dimensional manifolds. Using the results in [3], it can be shown that the slow manifold connects the two attracting branches of the critical set. For the dimerisation model, the critical set reduces to an incoming one dimensional manifold and an outgoing two dimensional manifold that intersect. By analysing this type of intersection using geometric desingularisation, we will show the existence of a transfer to the two dimensional manifold and determine the direction of the orbit on this manifold away from the intersection, in terms of the model parameters.
The General ProblemThe canonical form for the problem of interest is given bẏThe critical set is the union of the one dimensional manifold {x 2 = y, x 1 = 0 : y ∈ R} and the two dimensional manifold {x 2 = −y : x 1 , y ∈ R}. The incoming manifold S − a = {x 2 = y, x 1 = 0 : y < 0} is attracting.