Respiratory and inert gas exchange during high-frequency ventilation

Abstract

Pulmonary gas exchange during high-frequency low-tidal volume ventilation (HFV) (10 Hz, 4.8 ml/kg) was compared to conventional ventilation (CV) and an identical inspired fresh gas flow in pentobarbital-anesthetized dogs. Comparing respiratory and infused inert gas exchange during HFV and CV, the efficiency of oxygenation was not different but the Bohr physiological dead space ratio was greater on HFV (61.5 .+-. 2.2 vs. 50.6 .+-. 1.4%). Elimination of the most soluble inert gas (acetone) was markedly enhanced by HFV. The increased elimination of the soluble infused inert gases during HFV compared to CV may be related to the extensive intraregional gas mixing that allows the conducting airways to serve as a capacitance for the soluble inert gases. Comparing gas exchange during HFV with 3 different density carrier gases (He, N2 and Ar), the efficiency of elimination of CO2 or the i.v. infused inert gases was greatest with He-O2. Alveolar-arterial partial pressure difference for O2 on He-O2 exceeded that on N2-O2 by 5.4 torr during HFV. The finding agrees with similar observations during CV, suggesting that this aspect of gas exchange is not substantially altered by HFV.