Gas transport enhancement in high-frequency oscillation

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 CO2 partial pressures (PaCO2) decreased from 49.9 +/- 6.5 mm Hg (mean +/- SD) to 40.2 +/- 6.3 mm Hg (P less than 0.01) i.e. by 19.2 +/- 8.7%, and arterial O2 partial pressures (PaO2) increased from 71.5 +/- 13.1 mm Hg to 85.6 +/- 14.6 mm Hg (P less than 0.01) or by 20.5 +/- 12.0% in HFO-BT as compared to HFO+BT. At a fgf of 6 L/min, PaCO2 decreased less but still significantly (P less than 0.025) from 42.1 +/- 6.5 mm Hg to 37.8 +/- 6.8 mm Hg (10.4 +/- 5.6%) and PaO2 increased from 78.1 +/- 12.9 mm Hg to 84.6 +/- 16.4 mm Hg i.e. by 8.1 +/- 6.4% (P less than 0.05) in HFO-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.(ABSTRACT TRUNCATED AT 250 WORDS)