Determination of rheology and surface tension of airway surface liquid: a review of clinical relevance and measurement techniques

Abstract

By airway surface liquid, we mean a thin fluid continuum consisting of the airway lining layer and the alveolar lining layer, which not only serves as a protective barrier against foreign particles but also contributes to maintaining normal respiratory mechanics. In recent years, measurements of the rheological properties of airway surface liquid have attracted considerable clinical attention due to new advances in microrheology instruments and methods. This article reviews the clinical relevance of measurements of airway surface liquid viscoelasticity and surface tension from four main aspects: maintaining the stability of the airways and alveoli, preventing ventilator-induced lung injury, optimizing surfactant replacement therapy for respiratory syndrome distress, and characterizing the barrier properties of airway mucus to improve drug and gene delivery. Primary measuring techniques and methods suitable for determining the viscoelasticity and surface tension of airway surface liquid are then introduced with respect to principles, advantages and limitations. Cone and plate viscometers and particle tracking microrheometers are the most commonly used instruments for measuring the bulk viscosity and microviscosity of airway surface liquid, respectively, and pendant drop methods are particularly suitable for the measurement of airway surface liquid surface tension in vitro. Currently, in vivo and in situ measurements of the viscoelasticity and surface tension of the airway surface liquid in humans still presents many challenges.

Potential effect of pulmonary fluid viscosity on positive end-expiratory pressure and regional distribution of lung ventilation in acute respiratory distress syndrome

“…The cone and plate rheometer is the most commonly used device in the literature for measurement of pulmonary fluid viscosity (Lai et al 2009;Chen et al 2019). The current measurement is agreement with literature data on properties of pulmonary fluid macrorheology (Table 2).…”

Effects of the Lower Airway Secretions on Airway Opening Pressures and Suction Pressures in Critically Ill COVID-19 Patients: A Computational Simulation

“…The properties of these simulated lower airway secretions are comparable with those of healthy and diseased respiratory secretions. 3 , 18 One type of secretion simulants, such as sodium carboxymethyl cellulose (SCMC) and polyethylene oxide (PEO), 21 behaved like a pseudoplastic fluid and was therefore described by the power-law relationship, , where and m are the shear stress and the consistency of fluid, is the shear rate, and n is a measure of the degree of shear-thinning; the other type of secretion simulants, for example ghee, grease, peanut butter and mayonnaise, showed the behavior of a yield pseudoplastic fluid and was described by the Hershcel-Buckley model, , where is the yield stress.…”

Observations of, and Insights into, Cystic Fibrosis Mucus Heterogeneity in the Pre-Modulator Era: Sputum Characteristics, DNA and Glycoprotein Content, and Solubilization Time

“…CF mucus is more adherent, viscous, dehydrated, and impairs normal mucociliary escalator clearance [1,4,9,10,16,17,28,30,32,40,42,[49][50][51]. Alterations in, and macromolecular complexity of, CF secretions create physical and chemical barriers to the immune system, to regional ventilation, to antibiotic and mucolytic agents, and to potential gene therapy vehicles [4,37,48,50,[52][53][54][55][56]. CF mucus is a rich mixture of plasma proteins, inflammatory cells, DNA, bacteria, and bacterial products, with alveolar and tracheobronchial epithelial and submucosal gland secretions.…”

“…CF airway mucus is typically purulent, i.e., DNA content >0.025% of mucus dry weight, with the elevated DNA content affecting mucus viscosity, elasticity, and transport [37][38][39]45,47,52]. CF airway mucous glycoproteins may also be hypersecreted, defectively expanded, and/or hyperconcentrated, also impacting mucus character and MCC [4,17,18,28,31,36,40,42,51,56].…”