CO2 CONTROL OF BREATHING - PARAMETER-ESTIMATION AND STABILITY EVALUATION

A method is developed to evaluate system stability for the CO2 control of breathing in individuals by using data from the dynamics of CO2 re breathing and elimination. The theoretical basis of the method is a ph ysiological model of the CO2 respiratory control system and an explici t stability index (SI). The SI is algebraically related to the model p arameters: system volume (V-s), cardiac output (Q), circulatory transi t time (t(s)), and controller gain (G). A sequential optimization sche me is shown to yield estimates of the model parameters by comparing th e alveolar ventilation and PCO2 of the model output with corresponding experimental data. Model simulation of CO2 rebreathing and eliminatio n with different parameter values demonstrate that all parameters exce pt t(s) have significant effect an the outputs. Least-squares estimati on of the parameters using model-generated data with added noise showe d good precision for all parameters (except t(s)). This analysis is pe rformed with parameter values chosen to produce overdamped and underda mped responses that would occur in normal and abnormal respiratory con trol systems, respectively. It is anticipated that SI values of the (o verdamped) normal and (underdamped) abnormal systems differ by much mo re than the variation produced by imprecision of the parameter estimat es. For this circumstance, the method is expected to be sensitive enou gh to distinguish normal from abnormal CO2 respiratory control of indi vidual subjects.