Humidification of Base Flow Gas during Adult High-Frequency Oscillatory Ventilation:An Experimental Study Using a Lung Model

In adult high-frequency oscillatory ventilation (HFOV) with an R100 artificial ventilator, exhaled gas from patient s lung may warm the temperature probe and thereby disturb the humidification of base flow (BF) gas. We measured the humidity of BF gas during HFOV with frequencies of 6, 8 and 10Hz, maximum stroke volumes (SV) of 285, 205, and 160ml at the respective frequencies, and, BFs of 20, 30, 40l/min using an original lung model. The R100 device was equipped with a heated humidifier, HummaxⅡ, consisting of a porous hollow fiber in circuit. A 50-cm length of circuit was added between temperature probe (located at 50cm proximal from Y-piece) and the hollow fiber. The lung model was made of a plastic container and a circuit equipped with another HummaxⅡ. The lung model temperature was controlled at 37℃. The HummaxⅡ of the R100 was inactivated in study-1 and was set at 35℃ or 37℃ in study-2. The humidity was measured at the distal end of the added circuit in study-1 and at the proximal end in study-2. In study-1, humidity was detected at 6Hz (SV 285ml) and BF 20l/min, indicating the direct reach of the exhaled gas from the lung model to the temperature probe. In study-2 the absolute humidity of the BF gas decreased by increasing SV and by increasing BF and it was low with setting of 35℃. In this study setting, increasing the SV induced significant reduction of humidification of the BF gas during HFOV with R100.