A comparative study of respiratory models in control of ventilation

The aim of this work is to evaluate responses and characteristics of three respiratory models (RS1, RS2 and RS13) in the presence of the following stimuli: exercise, hypercapnia and hypoxia. A comparative study among the three closed-loop systems is performed in simulation: RS1 has a controller to minimize the mechanical and chemical work rate of breathing. RS2 and RS3 fit better to physiological systems with peripheral and central components. The steady state response is evaluated at different levels of stimulus by means of the variables: ventilation, PaCO₂ and PaO₂. In general, the stimulus and variable that produces more differences among models are exercise and ventilation, respectively. The best model to indicate the homeostasis during the exercise is RS1 but it is not possible to analyze hypoxia because there is no feedback of PaO₂. In the transient response, a settling time of several seconds is found in RS1 and a more realistic value around some minutes is obtained in the other models. Besides, whereas there are no overshoots in the responses of RS1, they appear in PaO₂ with RS2 and RS3 models because an exponential feedback of PaO₂ is considered. The influence of these time constants and gains on the transient response is analyzed to obtain the maximum values to keep the system stable. Finally, the sensitivity of the system response with the dead space is studied during exercise