Tracheal mucus clearance in high-frequency oscillation: Effect of peak flow rate bias

Abstract

We have reported previously that high-frequency oscillation of the chest wall (HFO/CW) enhances the tracheal mucus clearance rate (TMCR) in dogs. This enhancement of TMCR may be due in part to the expiratory bias in peak flow rate (V̇/V̇I>1) that occurs during HFO/CW. We examined this factor in 8 anaesthetized, spontaneously breathing dogs by comparing TMCR during the following manoeuvers: HFO/CW, applied by means of a thoracic cuff; 2) symmetric high-frequency oscillation via the airway opening (HFO/AO), applied by means of a piston pump driven by sinusoidal signal; 3) HFO/AO with an expiratory bias in peak flow, and 4) HFO/AO with an inspiratory bias in peak flow. All manoeuvers were of 5 min duration and were performed at 13 Hz and an oscillatory tidal volume of 1.5 ml·kg-1. In the latter two manoeuvers, the piston pump was driven by a nonsinusoidal signal such that peak V̇E/V̇(I) was greater than and less than unity, respectively. A high-impedance, cross-current flow of warmed, humidified air was provided at the tracheal tube. The order of manoeuvers 2, 3 and 4 was randomized, while manoeuver 1 was repeated at the end. TMCR was determined by direct bronchoscopic visualization of charcoal particle transport. Each HFO manoeuver was bracketed by a control period of spontaneous breathing. We found that TMCR during HFO/CW was 2.4 x control (p<0.001), in line with previous results. TMCR was not enhanced over control in any of the three HFO/AO manoeuvers; however, during HFO/AO with an expiratory peak flow bias, TMCR was consistently greater than during symmetric HFO/AO, or during HFO/AO with an inspiratory bias (p<0.01). The increase in TMCR due to expiratory-flow-bias HFO/AO (symmetric HFO/AO) was approximately 30% of the increase in TMCR due to HFO/CW.