Variability in tracheal mucociliary transport is not controlled by beating cilia in lambs in vivo during ventilation with humidified and nonhumidified air.

S J Kelly,V Brodecky,P J Berger,E M Skuza,S Tatkov

doi:10.1152/ajplung.00485.2020

Abstract

Mucociliary transport in the respiratory epithelium depends on beating of cilia to move a mucus layer containing trapped inhaled particles toward the mouth. Little is known about the relationship between cilia beat frequency (CBF) and mucus transport velocity (MTV) in vivo under normal physiological conditions and when inspired air is dry or not fully humidified. This study was designed to use video-microscopy to simultaneously measure CBF and MTV in the tracheal epithelium through an implanted optical window in mechanically ventilated lambs. The inspired air in 6 animals was heated to body temperature and fully saturated with water for 4 hours as a baseline. In another series of experiments, 5 lambs were ventilated with air at different temperatures and humidities and the mucosal surface temperature was monitored with infrared macro-imaging. In the baseline experiments, during ventilation with fully humidified air at body temperature, CBF remained constant, mean 13.9 ± 1.6 Hz but MTV varied considerably between 0.1 and 26.1 mm/min with mean 11.0 ± 3.9 mm/min, resulting in a maximum mucus displacement of 34.2 µm/cilia beat. Fully humidified air at body temperature prevented fluctuations in the surface temperature during breathing indicating a thermodynamic balance in the airways. When lambs were ventilated with dryer air, the mucosal surface temperature and MTV dropped without a significant change in CBF. When inspired air was dry, mainly latent heat (92%) was transferred to air in the trachea, reducing the surface temperature by 5 °C. Reduced humidity of the inspired air lowered the surface temperature and reduced MTV in the epithelium during ventilation.

Highlights

Mucociliary transport in conducting airways is a continuous process in which beating cilia propel mucus containing trapped inhaled particles along the respiratory epithelium [1] until they reach the mouth and are swallowed
In this study we present a technique that, by measuring both cilia beat frequency (CBF) and mucus transport velocity (MTV) simultaneously in vivo when lambs are ventilated with different air conditions, allows investigation of the relationship between CBF and MTV
The key finding from the first series of experiments was the variability in MTV and constant CBF during ventilation with body temperature pressure saturated (BTPS) air over 4 hours

Summary

Introduction

Mucociliary transport in conducting airways is a continuous process in which beating cilia propel mucus containing trapped inhaled particles along the respiratory epithelium [1] until they reach the mouth and are swallowed. Recent advances in the knowledge of cilia and mucus biology [6, 8, 9] highlight the importance of well-controlled interactions between cilia and the airway surface liquid for effective mucociliary transport. These interactions have been studied using a variety of models [10, 11] and in vitro experiments using frog palates [12,13,14], ferret [15], sheep and bovine tracheas [16, 17], and in vivo experiments with pig tracheas [18], mice airways [19, 20], and the human nasal cavity [21]. Environmental physiological conditions during the experiments were not controlled [18, 26, 27], both temperature and humidity of inspired air are known to play an important role in mucociliary transport [28,29,30,31]

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