Efficacy of Conventional and High-Frequency Ventilation at Altitude

摘要

High-frequency ventilation (HFV) is a promising mode of ventilatory support and could be useful in aeromedical evacuation. There have been no studies to date to examine the feasibility of maintaining gas exchange with HFV at reduced barometric pressure. This report investigates (1) The role of molecular diffusion in gas transport during HFV, and (2) The ability to maintain gas exchange with HFV at simulated altitude in healthy and in diseased lungs. The role of molecular diffusion was tested by determining the rate of pulmonary uptake of six tracer gases with low aqueous solubility but different molecular weights during conventional and high-frequency ventilation. The inspired gas and the subsequent rate of appearance of these gases in arterial blood were monitored. With conventional mechanical ventilation (CMV), there was separation of the gases with appearance in arterial blood occurring in order of increasing molecular weight. With HFV, there was a slight molecular weight effect, but substantially less than that seen with CMV. These findings indicate that the role of molecular diffusion during HFV is minimal, but a significantly greater effect of diffusion is present during CMV. Keywords: Aerodynamical evacuation; Ventilatory requirements; Air evacuation; Mechanical ventilation; High-frequency ventilation; Respirators. (KT)