A mathematical model and digital computer simulation of the human cardiovascular system and its controls are developed to simulate transient responses to bicycle ergometer exercise. The purpose of the model is to provide a method to analyze cardiovascular control hypotheses which cannot be tested easily in an animal or human. Complex cardiovascular control hypotheses are modeled for the control of heart period, peripheral flow resistances, venous tone, and other controlled variables. Control models are based on the use of proportional neurogenic controllers and linearized systems. Metabolic control models utilize simple mathematical models of oxygen uptake, oxygen deficit, and accumulating metabolites to simulate a transient metabolic state and indicate other chemical factors. Equations describing pulsatile blood flows, pressures, and volumes for 28 model sections of the uncontrolled cardiovascular circulatory system are solved. The circulatory system model is combined with the models of the controlling systems to simulate transient responses to exercise. Other characteristics of the combined model include gravity effects, muscle pumping, venous tone, venous valves, respiratory frequency, and intrathoracic pressure effects. Transient response characteristics and steady model values are presented and compared with experimental data. It is concluded that the neurogenic proportional controller hypothesis, combined with the metabolic control factors, can simulate sub-maximal exercise responses.

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