Influence of inspiratory-expiratory ratio on total resistance estimate in simulated mechanical ventilation

The effects of changing the inspiratory-expiratory ratio in mechanical ventilation on real-time estimates of total respiratory resistance were investigated by a computer simulation approach. An essential physiologically based model of breathing mechanics with six lumped parameters accounting for the main nonlinear viscoelastic properties of tracheobronchial airways was used for reproducing respiratory data in normal and airway obstructed conditions. Standard clinical ventilator setting was considered with a tidal volume of 600 ml and a respiratory frequency of 15 breaths/minute. Total inspiratory and expiratory resistances and elastances were estimated on-line using the time-varying one-compartment first-order model of the respiratory mechanics. Greater expiratory resistances were found in agreement with literature. The on-line approach supplied trustworthy estimates of both end-inspiratory and end-expiratory resistances. The percentage difference between these two values can give information about important physiopathological aspects related to series localization of airway obstructions and it seems not to be very sensitive to changes in the inspiratory-expiratory ratio.