The BathRC model: a method to estimate flow restrictor size for dual ventilation of dissimilar patients

Andrew R Plummer; Jonathan l du Bois; Siu Man Lee; Patrick Magee; Jens Roesner; Harinderjit S Gill

To illustrate the change in behaviour and model fit at a different condition, Tests 4 and 5 use an inspiration pressure rise (Pinsp) of 15 instead of 25 cmH20. Comparing lung 1 flow without and with the fixed restrictor -Test 4 ( Figure 13 ) and Test 5 ( Figure 14) -shows the expected reduction in flow and a tidal volume drop of 20%, again associated with a small increase in lung 2 tidal volume (6%). An issue which can be seen in the flow plots in Figures 13a and 14a is the lung 1 flow measurement at around 4 s, where the flow sudden becomes zero. This is a low-flow drop out characteristic of that specific flow meter, but the influence on results is thought to be small. Table 2 , the RC model predicts the tidal volumes reasonably well for this range of conditions. For lung 1, in the five tests the measured tidal volume deviates from the predicted by 2.4%, -3.6%, 3.5%, -5.6% and-9.3% respectively. For lung 2, the measured tidal volume deviates from the predicted by 1.4%, 4.9%, 6.3%, -4.4% and 1.4% respectively. The largest absolute error is 31 mL. For comparison, in [1] a tidal volume change of up to ±100 mL total for both patients together after their transfer from single to dual ventilation with nominally the same settings is considered acceptable.