Figure 1. The experimental setup used in this study inserted between the Y piece of the ventilator circuit and the endotracheal tube. 1 = Y piece of the ventilator circuit; 2 = pneumotachograph; 3 = heat and moisture exchange filter; 4 = entry or proximal pressure; 5 = exit or distal pressure measured with a catheter placed within the endotracheal tube; 6 = pressure transducer.