Gas transport enhancement in high-frequency oscillation

Abstract Gas transport during high-frequency oscillation (HFO) with (HFO +BT ) and without bias tube (HFO −BT ) was investigated in 10 anesthetized supine dogs. The oscillatory volume effectively delivered to the lungs, airway occlusion pressure and lung volume above functional residual capacity (FRC), regulated by a newly deviced pressure control system, as well as the oscillatory frequency (20 Hz) were adjusted to equal levels in HFO +BT and HFO −BT . At a fresh gas flow rate (fgf) of 3 L/min (room air), arterial CO 2 partial pressures (Pa CO 2 ) decreased from 49.9 ± 6.5 mm Hg (mean ± SD) to 40.2 ± 6.3 mm Hg ( P i.e. by 19.2 ± 8.7%, and arterial O 2 partial pressures (Pa O 2 ) increased from 71.5 ± 13.1 mm Hg to 85.6 ± 14.6 mm Hg ( P −BT as compared to HFO +BT . At fgf of 6 L/min, Pa CO 2 decreased less but still significantly ( P O 2 increased from 78.1 ± 12.9 mm Hg to 84.6 ± 16.4 mm Hg i.e. by 8.1 ± 6.4% ( P −BT . The higher gas transport efficiency after removing the bias tube can be explained by two mechanisms: (1) By removing the bias tube, the volume of the bias system decreased from 54 ml in HFO +BT to 1 ml in HFO −BT and rebreathing of exhaust gas from the bias system is therefore eliminated in HFO −BT . (2) In HFO, the inspiratory gas consists of exhaust gas from the previous expiration, fresh gas from the fresh gas flow and gas, which was pulled into the HFO circuit during the preceding expiratory half cycle through the bias system. As at a constant oscillatory volume, effectively delivered to the lungs, the oscillatory volume at the exit of the bias system increased considerably in HFO −BT , the exhaust gas from the previous expiration was more efficiently diluted in HFO −BT .