High frequency jet ventilation (HFJV) experiments were performed in healthy anaesthetized mongrel dogs via a multilumen tracheal jet tube to examine the influence of gas flow, ventilatory frequency and inspiration time (as a percentage of the total ventilatory cycle) on gas exchange. We compared arterial PO2, PCO2 and cardiac output during periods of adequate intermittent positive pressure ventilation (IPPV) and periods of HFJV. Reducing gas flow by decreasing the number of activated valves and increasing the frequency to greater than 4 Hz resulted in less than optimal arterial PO2 and PCO2 compared with IPPV. This indicates that convection during HFJV is probably essential for efficient gas exchange. Inspiration time proved to be important in determining efficacy of ventilation for a fixed ventilator minute volume. Cardiac output during all HFJV settings was equal to or greater than cardiac output during IPPV, even as those HFJV settings that resulted in a positive end-expiratory pressure.

During distal high frequency jet ventilation (HFJV) in anaesthetized healthy dogs gas flows were recorded at the proximal end of the open tracheal jet tube. Spirometer measurements of minute volumes with and without entrainment were made. During the inspiratory or insumation period, leakage of jet gas (bypass) could occur depending on the ventilator setting. From the gas flow recordings and the spirometer measurements, jet-, entrainment-and bypass minute volumes were determined. From these the effective minute volume, that is the minute volume of fresh gas entering the lungs, was calculated, as well as tidal volume. The results show that entrainment volumes are relatively small in an open system of distal HFJV and that at the same time bypass can (nearly) completely eliminate the effect of entrainment on tidal volume.

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To investigate the influence of changes in thorax and lung compliance on ventilation during distal High Frequency Jet Ventilation (HFJV), similar ventilator settings were compared before and after changing the compliance in two groups of anaesthetized mongrel dogs. Each period of distal HFJV was preceded by adequate Intermittent Positive Pressure Ventilation (IPPV) to assure a start with baseline values. In Group 1 (n = 7), thorax compliance was changed by chest strapping, while in Group 2 (n = 7) lung compliance was changed by inducing acute lung injury by injection of oleic acid into the right atrium. Gas flow distribution in the ventilatory circuit during distal HFJV was determined before and after the changes in compliance were induced. Comparing similar ventilator settings during distal HFJV in the same dog, a decrease in lung or thorax compliance led to changes in gas flow distribution in the ventilatory circuit. Entrainment was decreased and bypass increased with a negative effect on the gas volume entering the lungs and on gas exchange. The results indicate that distal HFJV should be regarded as pressure-limited ventilation.