Investigation of cardiorespiratory abnormalities through computer simulation

Abstract

The basic physiologic functions which were simulated on the digital computer are multiple alveolar ventilation through a branching bronchial structure, the distribution of alveolar ventilation across the lung based on airway resistance and alveolar compliance, O 2 and CO 2 exchange with and transport in the blood, ventilation control based on arterial blood P a co 2, P a o 2 and pH a , and peripheral metabolic exchange of O 2, CO 2, and acid or base. The simulation output is a set continuous-time variables corresponding to clinical measurements, namely: volume, rate and composition of expired gas, composition of arterial and venous blood, indicator dilution across the heart and lung, and intraplural pressure used to obtain dynamic lung compliance and resistance. The simulation was used to investigate the observability (based on the clinical measurements) of changes in ventilation and perfusion distributions and to evaluate the ability of the lung to control acid-base balance with normal and reduced lung compliance for a range of metabolic CO 2 production and acid or base, compatible with those observed in critically ill patients in decompensated septic shock.