Objective <p>Understanding driving pressure is of general interest in lung mechanics, especially in ventilated neonatal and pediatric patients. The aim of this study was to investigate the effects of endotracheal tube size (ETT) and bi-directional linear flow resistors mimicking different degrees of tube and airway obstruction on tracheal pressure (P_tr) during ventilation with decelerating flow.</p> Methods <p>A mechanical lung simulator with unchanged respiratory mechanics like the mimicked compliance and resistance, three ETTs (inner diameters of 7.5&#xa0;mm, 5.5&#xa0;mm, and 3.5&#xa0;mm), and four different linear flow resistors were alternatively connected to a commercial ventilator operating in pressure-controlled mode. Four resistors mimicking various degrees of ETT obstructions were placed consecutively between the Y-piece and the ETT. Varying sequentially ETT size, resistance, and ventilator settings resulted in 90 sets of measurements. Data acquisition, signal processing, and data analysis were performed using Python.</p> Results <p>The results clarify that decreasing ETT sizes and increasing flow resistances cause an increase in the time necessary to reach zero-flow conditions both during in- and expiration. This results in a decrease of P_tr at the end of inspiration and an increase of P_tr at the end of expiration, if inspiratory and expiratory times remain unchanged.</p> Conclusion <p>The degree to which peak inspiratory pressure overestimates P_tr (or plateau pressure) in decelerating flow can be substantial and increases with increasing flow resistance. This highlights the importance of measuring plateau pressure or P_tr to understand pressure dynamics delivered to the lung.</p>