Gaseous homeostasis and the circle system. Description of a model.

A model has been constructed of a subject breathing from a circle system. The subject model is based on the circulation-time model of anaesthetic uptake described by Mapleson. This is a multi-compartmental model of body tissues in which gas exchange in each compartment is calculated at each heart beat. The lung compartment of Mapleson's model has been modified to allow for an unlimited number of gases to be present in the inspired gas mixture. The circle system model assumes total absorption of all expired carbon dioxide and full mixing of all gases within the system. The volume of gas in the system and its composition is calculated for each respiratory cycle. The subject model can be considered as being either attached to a non-rebreathing system, when inspired gas composition is under the control of the operator, or attached to the circle system, when the operator has control of fresh gas flow and composition. The model has been realized as a computer program written in Pascal.