RESPIRATORY ANALOG-COMPUTER MODEL

An analogue computer model has been constructed to simulate the dynami c behaviour of the human cardiorespiratory system for studying the eff ect of changes in different system-variables-as alveolar ventilation, functional residual capacity (FRC) of the human lung and the cardiac o utput-on the partial pressure of carbon dioxide in the arterial and mi xed venous blood (pCO(2a),pCO(2v)). The respiratory analogue computer model (RACM) simulates reliably well-known clinical physiological as w ell as pathological phenomena. Reducing FRC or breath rate an oscillat ion of pCO(2a) has been developed, but the mean value has not been cha nged. In alveolar hypoventilation the pCO(2) of blood increases in goo d conformity with the clinical experience. Reducing cardiac output a c haracteristic dissociation appeared: pCO(2v) and pCO(2a) diverged from each other by increasing pCO(2v) and decreasing PCO2a. Since in gener al clinical practice of intensive care only arterial blood gas values are checked regularly, the conclusion that the patient's condition is improving by decreasing pCO(2a) is a serious misinterpretation in this case, because peripheral tissues are in balance with the increasing v enous carbon dioxide tension, and consequently cannot get rid of this toxic agent. The computer-model-based conclusion has led to the practi ce of sampling both arterial and venous carbon dioxide tensions for be tter slate assessment of seriously ill patients.