Acoustic reflectometry for estimation of lung gas-phase volume during partial liquid ventilation in sheep

Abstract

Acoustic reflectometry was studied as a possible tool to measure the lung gas-phase volume during partial liquid ventilation (PLVSM). With IRB approval, healthy sheep (weight 10–22 kg) (n=3) were anesthetized, intubated, mechanically ventilated in the supine position, and underwent a low-lying tracheostomy. A base-line functional residual capacity (FRC) via a N2 washout technique was measured. Perflubron (LiquiVent®, Alliance Pharmaceutical Corp., San Diego, CA) was instilled through the tracheostomy tube in successive aliquots, each consisting of 20% of measured FRC, up to 100% FRC. A Hood Labs acoustic reflectometer was used to obtain lung gas volume determinations for the FRC measurement and after perflubron instillations. The acoustic reflectometer was used to generate a cross-sectional area versus axial length curve. The subglottic lung gas-phase volume was calculated by integrating area over length. The reduction in the subglottic lung gas-phase volumes for each animal exhibited a strong linear correlation with the amount of perflubron instilled. Linear least-squares regression models run on the individual sheep data were all significant, with the largest p value being 0.0067. Acoustic reflectometry may be of use in the monitoring of lung gas-phase volume in PLV and respiratory disease.