Mathematical simulation of the human circulatory system

A digital model of the human circulatory system has been developed which simulates pulsatile blood flow and gas transport and exchange. The model was designed specifically to study short term G stress encountered in modern aerial combat manuevers and incorporates a realistic representation of the nonlinear elastic characteristics of circulatory elements and the related pressure dependent flow resistance characteristic of these elements. One form for the pressure-volume relationship used in the model was shown to fit in vivo data for arteries, veins, and left atrium. The resistance-pressure relationship which follows using the Poiseuille-Hagen formula was shown to fit lung data. The oxygen saturation curve and the carbon dioxide dissociation curve were represented by published equations. The systemic circulation is partitioned into four zones: head, upper torso, lower torso, and legs; while the pulmonary circulation is partitioned into six zones with a corresponding distribution of ventilation. This model has been shown to properly simulate experimental human data for passive breathing in a prone subject. The computed carbon dioxide and oxygen partial pressures vary realistically around measured average partial pressures from human subjects. The computed blood pressure-time, volume-time, and flow-time curves match corresponding curves for human data. Under sinusoidal variations G[lowered z], the model predicts realistic variations of body segment volumes, flows and pressures.