An empirical model of end-tidal CO2 response to minute ventilation

This paper presents an empirical model of end-tidal CO2 (PETCO2) response to minute ventilation (MV) for use in the closed-loop control of artificial respiration. An affine model structure consisting of a linear dynamic system followed by an affine transform is presented. It is proposed that this derives a low-order, high-fidelity representation of the respiratory process that can describe the positive and inversely proportional relationship between PETCO2 and MV. The efficacy of the model is evaluated using experimental respiratory data from 18 human subjects. The model performed well with a root-mean-squared error (RMSE) of 0.22+/−0.15mmHg and a coefficient of determination (r²) of 0.81+/−0.18 (mean+/−SD) when a 2^nd-order rational transfer function was used as the linear component of the model. The physiologic implication of the model is analyzed by comparison with a traditional compartment model that is widely used in pharmacological modeling.