INCREASE IN TRACHEAL PRESSURE DURING JET VENTILATION

Gas injection is a process that may be used to supplement other modes of artificial ventilation or be used alone. Its main effects include air entrainment and improvement in gas transport. The first effect may be seen best in periodic, axial injection of gas through a tracheal tube, as occurs in high frequency jet ventilation (HFJV) [1, 2]. In this type of jet ventilation, a considerable volume of air is entrained; thus the tidal volume is much larger than the injected volume. The second effect has been essentially described in constant flow ventilation (CFV), an experimental mode of ventilation proposed recently [3, 4], in which a constant flow of gas, injected near the inner walls of the first airway bifurcation by means of a double catheter, provides gas mixing in the apnoeic lung. This results in bidirectional convective streaming in a proximal turbulent jet region. Another application is the use of lateral or perpendicular jets to deliver fresh gas in the tracheal tube during high frequency oscillation (HFO) [5], which has been found to play a beneficial role in oscillatory gas transport [6]. However, fundamental studies are needed for improved understanding of these two effects: the magnitude of the actual tidal volume during HFJV is not known, and the dimensions of the turbulent jet region during CFV are uncertain. In the clinical field, air entrainment phenomena related to gas injection in the airways are so poorly understood as to be confused with the Venturi effect [7]. However, gas injection in the airways obeys a different physical law; the relevant phenomenon is pressure increase in the airways. Although this effect has often been observed during jet ventilation [2, 4, 5], it has not been analysed in physical studies, with the exception o