Control processes in human respiration

Cannings, Ross (1977) Control processes in human respiration. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

This thesis attempts to define an optimum control strategy for human respiration by modelling the chemical, mechanical and neural processes within the system. Each aspect of respiration is considered in turn, so that ultimately, a unified system approach may be adopted to gain insight into the controlling mechanisms.The mechanics of the ventilatory pump are viewed in terms of a diaphragmatic breathing model which makes it possible to describe the low level mechanical control loops using simple feedback models. A study of the optimum breathing patterns and frequencies is also performed. The results from these studies, in conjunction with recent experimental evidence, allow the mechanics of respiration to be represented in terms of the neural output of the respiratory centre and enable a realistic sub-optimal mechanical control policy to be proposed. This is felt to be of considerable importance when modelling system performance as a whole.Chemical features of the system are described by the well established chemostat principle, which is ~tended to allow the inclusion of breath by breath effects and hence form a link between the chemical and mechanical aspects of respiration. The behaviour of the chemostat is extensively analysed in relation to the requirements of a breathing optimization study. It is demonstrated that an analytic solution to the system equations only exists under a very restricted set of mechanical conditions and that formulation of the optimization problem in terms of the Maximum Principle results in a complex two point boundary value problem. However various performance criteria can be tested by making use of the sub-optimal mechanical control policy. Hard and soft constraints are employed to describe the allowable variations in blood gas chemistry, and ultimately it is suggested that steady state system operation can be formulated in terms of a small class of performance criteria.

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