Airway pressure measurement during high frequency oscillatory ventilation.

We developed a method to measure accurately pressures at the airway opening (Pao) and in the trachea (Ptr) in neonates during high frequency oscillatory ventilation (HFOV) from 15-30 Hz. All component parts of the pressure-measuring system were tested as a unit against a reference transducer in a closed chamber in which sinusoidal pressure waves could be generated. The resulting waveforms were displayed on an oscilloscope and measured. Ptr was measured through the intramural lumen of a Hi-Lo jet tracheal tube (National Catheter Co., Argyle, NY) opening 1 cm above the distal tip. Pressure readings from uncorrected waveforms indicated a discrepancy between measured and actual pressures, as high as 100% at frequencies of 100 Hz. When the resonance of the system was damped with a CorrecTORR (Norton Health Care Products, Akron, OH), the ratio of test to reference transducer output was flat +/- 5% from 0-160 Hz for the Pao system and flat +/- 4% from 0-100 Hz for the Ptr system. Ptr system accuracy was verified in an excised rabbit lung and the systems were used clinically in neonatal HFOV. We conclude that Pao and Ptr can be measured accurately during HFOV by this method.