Comparison of the ventilation characteristics in two adult oscillators: a lung model study.

BACKGROUND: Two recent large randomized controlled trials did not show the superiority of high-frequency oscillatory ventilation (HFOV) in adults with ARDS. These two trials had differing results, and possible causes could be the different oscillators used and their different settings, including inspiratory time % (IT%). The aims of this study were to obtain basic data about the ventilation characteristics in two adult oscillators and to elucidate the effect of the oscillator and IT% on ventilation efficiency.

METHODS: The Metran R100 or SensorMedics 3100B was connected to an original lung model internally equipped with a simulated bronchial tree. The actual stroke volume (aSV) was measured with a flow sensor placed at the Y-piece. Carbon dioxide (CO2 ) was continuously insufflated into the lung model ([Formula: see text]CO2 ), and the partial pressure of CO2 (PCO2 ) in the lung model was monitored. Alveolar ventilation ([Formula: see text]A; L/min) was estimated as [Formula: see text]CO2 divided by the stabilized value of PCO2 . [Formula: see text]A was evaluated with several stroke volume settings in the R100 (IT = 50%) or several airway pressure amplitude settings in the 3100B (IT = 33%, 50%) at a frequency of 6 and 8 Hz, a mean airway pressure of 25 cmH2 O, and a bias flow of 30 L/min. Assuming that [Formula: see text]A = frequencya  × aSVb , values of a and b were determined. Ventilation efficiency was calculated as [Formula: see text]A divided by actual minute ventilation.

RESULTS: The relationship between aSV and [Formula: see text]A or ventilation efficiency were different depending on the oscillator and IT%. The values of a and b were 0 < a < 1 and 1 < b < 2 and were different for three conditions at both frequencies. [Formula: see text]A and ventilation efficiency were highest with R100 (IT = 50%) and lowest with 3100B (IT = 33%) for high aSV ranges at both frequencies.

CONCLUSIONS: In this lung model study, ventilation characteristics were different depending on the oscillator and IT%. Ventilation efficiency was highest with R100 (IT = 50%) and lowest with 3100B (IT = 33%) for high aSV ranges.