Modeling of the expiratory flow pattern of spontaneously breathing cats

A mathematical model was developed describing the entire expiratory flow pattern during spontaneous, tidal breathing in the absence of expiratory muscle activity. It provides estimates for the time constants of the respiratory system (τRSmodel) and of the decay of continuing inspiratory muscle activity in early expiration (τmusmodel). In ten anesthetized, tracheostomized cats flow, tracheal pressure and diaphragmatic EMG were measured during normal expirations and expirations with four different added resistances. No significant differences were found between τRSmodel (0.21-0.49 sec) obtained by fitting the model to the flow data and τRS obtained from the straight part of the expiratory flow-volume curve. τmusmodel (0.050-0.052 sec) was comparable to similar time constants obtained from the integrated diaphragmatic EMG or from end-inspiratory, tracheal occlusion pressure. Fitted peak flow and time to peak tidal expiratory flow were not significantly different from those measured. In conclusion, for spontaneously breathing, anesthetized cats our model provides a close fit of the expiratory flow and parameter estimates were comparable with independently measured values.

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