LAUSR

To provide an in vitro estimation of the pressure drop across tracheal tubes (ΔP TT ) in the face of given pulsatile frequencies and peak pressures (P work ) delivered by a high-frequency percussive ventilator (HFPV) applied to a lung model. Tracheal tubes (TT) 6.5, 7.5 and 8.0 were connected to a test lung simulating the respiratory system resistive (R = 5, 20, 50 cmH 2 O/L/s) and elastic (C = 10, 20, and 50 mL/cmH 2 O) loads. The model was ventilated by HFPV with a pulse inspiratory peak pressure (work pressure P work ) augmented in 5-cmH 2 O steps from 20 to 45 cmH 2 O, yielding 6 diverse airflows. The percussive frequency ( f ) was set to 300, 500 and 700 cycles/min, respectively. Pressure (Paw and Ptr) and flow (V’) measurements were performed for all 162 possible combinations of loads, frequencies, and work pressures for each TT size, thus yielding 486 determinations. For each respiratory cycle ΔP TT was calculated by subtracting each peak Ptr from its corresponding peak Paw. A non-linear model was constructed to assess the relationships between single parameters. Performance of the produced model was measured in terms of root mean square error (RMSE) and the coefficient of determination (r 2 ). ΔP TT was predicted by P work (exponential Gaussian relationship), resistance (quadratic and linear terms), frequency (quadratic and linear terms) and tube diameter (linear term), but not by compliance. RMSE of the model on the testing dataset was 1.17 cmH 2 O, r 2 was 0.79 and estimation error was lower than 1 cmH 2 O in 68% of cases. As a result, even without a flow value, the physician would be able to evaluate ΔP TT pressure. If the present results of our bench study could be clinically confirmed, the use of a nonconventional ventilatory strategy as HFPV, would be safer and easier.