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Exhaled particles and small airways

Journal article
Authors Björn Bake
Göran Ljungkvist
Evert Ljungström
Anna-Carin Olin
Published in Respiratory Research
Volume 20
ISSN 1465-993X
Publication year 2019
Published at Institute of Medicine, School of Public Health and Community Medicine
Department of Chemistry and Molecular Biology
Institute of Medicine, Department of Internal Medicine and Clinical Nutrition
Language en
Keywords Exhaled particles, Small airways, Airway closure, Airway opening, Surfactant, Proteomics, SP-A, Albumin, DPPC, POPC, surfactant protein-a, breath n-2 test, regional-distribution, endogenous, particles, lung-volumes, obstruction, closure, methadone, size, site, Respiratory System, licemi.j, 1966, journal of applied physiology, v21, p749
Subject categories Respiratory Medicine and Allergy


BackgroundOriginally, studies on exhaled droplets explored properties of airborne transmission of infectious diseases. More recently, the interest focuses on properties of exhaled droplets as biomarkers, enabled by the development of technical equipment and methods for chemical analysis. Because exhaled droplets contain nonvolatile substances, particles is the physical designation. This review aims to outline the development in the area of exhaled particles, particularly regarding biomarkers and the connection with small airways, i e airways with an internal diameter<2mm.Main bodyGeneration mechanisms, sites of origin, number concentrations of exhaled particles and the content of nonvolatile substances are studied. Exhaled particles range in diameter from 0.01 and 1000m depending on generation mechanism and site of origin. Airway reopening is one scientifically substantiated particle generation mechanism. During deep expirations, small airways close and the reopening process produces minute particles. When exhaled, these particles have a diameter of <4m. A size discriminating sampling of particles <4m and determination of the size distribution, allows exhaled particle mass to be estimated. The median mass is represented by particles in the size range of 0.7 to 1.0m. Half an hour of repeated deep expirations result in samples in the order of nanogram to microgram. The source of these samples is the respiratory tract ling fluid of small airways and consists of lipids and proteins, similarly to surfactant. Early clinical studies of e g chronic obstructive pulmonary disease and asthma, reported altered particle formation and particle composition.ConclusionThe physical properties and content of exhaled particles generated by the airway reopening mechanism offers an exciting noninvasive way to obtain samples from the respiratory tract lining fluid of small airways. The biomarker potential is only at the beginning to be explored.

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