Influence of endotracheal tube bore on tidal volume during high frequency oscillatory ventilation: A model lung study

Background: In adults, the influence of endotracheal tube bore on tidal Volume (V-T) during high-frequency osciallatory ventilation (HFOV) has been little studied. Material/Methods: Via full-length 6, 7, 8, and 9 min internal diameter (ID) endotracheal tubes (ETFs), a model lung (TTL, Michigan Instruments, MI) was ventilated using a high-frequency oscillator designed for adult patients (R100; Metran, Japan). Oscillation settings were: frequency, 5, 7, and 9 Hz; mean airway pressure, 15 cmH(2)O; oxygen inspiratory fraction, 0.21. At each setting: oscillator pressure swing was set at maximum; and each test combination was conducted with the modelling compliance set at 20 and 50 mL/cmH(2)O. During the trials, a position sensor attached to the model-lung upper surface provided analog electrical signals for lung movement that were converted to V-T evaluation data. Pressure and volume signals were digitized using an analog-to-digital converter and recorded in a computer. At each setting, three waveforms were analyzed and the average value used. Results: At each setting, measured V-T was proportional to ETT internal cross-sectional area (CSA). Regression analysis of VT showed correlation with the CSA, as expressed by formula, y=2.173x where x is CSA and y is V-T (R-2=0.99, p<0.001) at 5 Hz and compliance of 50 cmH(2)O. Conclusions: In an adult-simulating model lung, V-T during HFOV varies in proportion to ETT CSA.