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 (VE/VI greater than 1) that occurs during HFO/CW. We examined this factor in 8 anaesthetized, spontaneously breathing dogs by comparing TMCR during the following manoeuvers: 1) 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 VE/VI 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 less than 0.001), in line with previous results.(ABSTRACT TRUNCATED AT 250 WORDS)

Simultaneous measurement of force and respiratory profiles during chest physiotherapy in ventilated children

“…It may be assumed that the early rapid compression force is responsible for the increase in expiratory airflow and that the oscillatory component is more important in terms of altering the mucus properties. An increase in mucus transport has been linked to increased airway oscillation, which is believed to decrease the viscosity of mucus and increase the expiratory air flow (Chang et al 1988, Gross et al 1985, King et al 1990. The exact relationship between applied force and resultant flow changes will be determined by a number of factors including the timing of applied force during the respiratory cycle, age of the child and underlying pathophysiology which will need to be explored thoroughly in future clinical studies.…”

Identifying and Understanding Risk Factors for Instability and Adverse Events Associated With Chest Physiotherapy in Ventilated Children

“…High frequency chest wall oscillation provided at the mouth by a pistol pump did not improve tracheal mucus clearance rate in mechanically ventilated dogs (King et al, 1984). However in a follow up study mucus transport rates increased by 99% (+/-11) during high frequency oscillation with an expiratory flow bias compared to control (King et al, 1990). The Metaneb is a new generation IPV device, which provides a simultaneous combination of positive pressure, continuous high frequency oscillations and aerosol delivery (Ferguson and Wright, 2017).…”

“…Factors favouring two phase gas liquid flow transport in-vivo include: the inclined orientation of airway branches which may reduce the influence of gravity, and the presence of the PCL which will aid movement of the mucus layer (Kim et al, 1987, Kim et al, 1986b. Animal studies have demonstrated cephalad movement of mucus in situations with an expiratory flow bias (Benjamin et al, 1989, King et al, 1990)…”

“…In early studies the use of a mechanical cuff to deliver CWV demonstrated an increase in peripheral mucus clearance index in mechanically ventilated dogs and a 2.4 times improvement in tracheal mucus clearance rate in a lung model (Gross et al, 1985, King et al, 1990. However in practice CWV are a manual 'hands-on' therapy.…”