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Review
. 2019 Nov 20;28(154):190046.
doi: 10.1183/16000617.0046-2019. Print 2019 Dec 31.

Lung clearance index: assessment and utility in children with asthma

Amy G L Nuttall  1   2 , Werner Velásquez  3 , Caroline S Beardsmore  1   2 , Erol A Gaillard  4   2
Affiliations
Review

Lung clearance index: assessment and utility in children with asthma

Amy G L Nuttall et al. Eur Respir Rev. .

Abstract

There is increasing evidence that ventilation heterogeneity and small airway disease are significant factors in asthma, with evidence suggesting that the small airways are involved from an early stage in childhood asthma. Spirometry is commonly used to monitor lung function in asthmatics; however, it is not sensitive to small airway disease. There has been renewed interest in multibreath washout (MBW) tests, with recognition of the lung clearance index (LCI) as a global index of abnormality in gas mixing of the lungs that therefore also reflects small airway disease. This review summarises the technical and practical aspects of the MBW/LCI in children, and the differences between commercially available equipment. Children with severe asthma are more likely to have an abnormal LCI, whereas most children with mild-to-moderate asthma have an LCI within the normal range, but slightly higher than age-matched healthy controls. Monitoring children with asthma with MBW alongside standard spirometry may provide useful additional information.

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Conflict of interest statement

Conflict of interest: A.G.L. Nuttall has nothing to disclose. Conflict of interest: W. Velásquez has nothing to disclose. Conflict of interest: C.S. Beardsmore has nothing to disclose. Conflict of interest: E.A. Gaillard reports grants from Chiesi Ltd, Gilead and Circassia, non-financial support and other funding from Medimmune, travel grants from Vertex, and consultancy fees from Boehringer Ingelheim and Anaxsys, outside the submitted work.

Figures

FIGURE 1
FIGURE 1
a) Nitrogen concentration and volume tracings as a function of time during a multibreath washout test obtained during histamine provocation. b) Illustration of alveolar slope in nitrogen versus expired volume for breaths 1 and 20 plotted in an equivalent scaling with respect to mean nitrogen expired concentration of breaths 1 and 20, respectively. Reproduced from [38] with permission from the publisher.
FIGURE 2
FIGURE 2
Schematic plot of normalised phase III slopes (SnIII) against turnover as washout progresses. The axis TO (turnovers) represents breath number. The solid line (labelled total) represents the combined effect of acinar and conducting inhomogeneity. The slope of the linear portion of this line (Scond; usual index of ventilatory inhomogeneity in the conducting airways) is conventionally calculated from data points between 1.5 and 6 turnovers [39]. The simple dashed line (CDI; convection dependent inhomogeneity) is a transposition of the slope so that it passes through the origin, thereby representing purely the inhomogeneity in the conducting airways. Diffusion–convection dependent inhomogeneity (DCDI) initially contributes more to overall inhomegeneity (rises for first five breaths), but remains unchanged subequently. The index of ventilatory inhomogeneity within the acinar airways (Sacin) is calculated by identifying the normalised phase III slope of the first breath and subtracting Scond from this value. Reproduced from [39] with permission from the publisher.
FIGURE 3
FIGURE 3
An example set-up of equipment for multibreath washout testing.
See this image and copyright information in PMC

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