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Chapter 6 – High Frequency Percussive Ventilator characterization
point demarks a switch from an initial model in which inhaling is induced to a second model
in which exhalation occurs freely. The two models are different each other about the estimate
of inhaled and exhaled resistance; in this way, it is possible to obtain a significant adaptation
to the experimental data, without loss of accuracy in parameters estimate [Barbini P. et al
2001]. We will not consider the second model, concerning the expiratory phase, because
clinical parameters of our interest are mainly related to the inspiratory phase. A second
operation concerns the estimation of resistance and elastance values by using the method
previously described applied on data acquired during the inspiratory period of the analyzed
respiratory cycle. Such values are updated every respiratory cycle and utilized to construct the
pressure curve generated by the model using the measured flow as input. This estimated
pressure curve is compared to the corresponding measured pressure curve in order to verify
the validity of the model. The mean square error is used to measure the differences between
measured and modelled pressures. This procedure runs during the expiratory phase,
visualizing the estimated curve superimposed to the measured one in the inhalation phase.
The operations are repeated for each respiration cycle.
The figure 6.2 shows the ANSI-C implementation of described algorithm.
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