MECHANICAL SIMILARITIES OF A HIGH FREQUENCY JET VENTILATOR AND A CONVENTIONAL VENTILATOR

Abstract

The outputs of a Healthdyne Jet (HJ) and a Baby Bird (BB) ventilator were compared by ventilating a neonatal lung model with physiological resistance and compliance. We measured alveolar pressure (Palv), change in lung volume ( ΔLV) and tidal volume (V_T) over the frequency (f) range of each ventilator (80-900 BPM and 20-100 BPM respectively) using a variety of I:E ratios, peak pressures, end expiratory pressures, and flow rates. The relationships of Palv, LV and V_T to f were similar in both ventilators. Palv and LV increased similarly by increasing frequency. This effect was magnified by increasing I:E ratio or flow rate. V_T decreased in both ventilators according to a hyperbolic relationship (x·y=constant). A conventional and jet ventilator have very similar mechanical output and pressure and volume relationships over their frequency ranges. This similarity derives in part from similarity of design and in part from interaction between the ventilator and the ventilated object.

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