Age Dependence Of Small Airways Ventilation Heterogeneity

<span style="font-family: 'Times','serif'; font-size: 12pt; mso-ansi-language: EN-US; mso-fareast-font-family: Times; mso-bidi-font-family: 'Times New Roman'; mso-fareast-language: IT; mso-bidi-language: AR-SA;" lang="EN-US">Functional closure of small airways can occur during tidal breathing above functional residual capacity (FRC) both in asthma and COPD patients, especially during exacerbations. Such event has several noxious consequences on gas exchange, airway hyperresponsiveness and mechanical stress and strain within lung tissue and airway wall, mostly due to increase in ventilation heterogeneity. The availability of simple functional tests based on sequential measurements of lung volumes (i.e.: FRC), by plethysmography and dilutional techniques may reveal and monitor easily tidal airway closure that can be and should be treated with the aim of abolishing or at least reducing this dangerous condition.</span>

Download Full-text

Lung clearance index: assessment and utility in children with asthma

European Respiratory Review ◽

10.1183/16000617.0046-2019 ◽

2019 ◽

Vol 28 (154) ◽

pp. 190046 ◽

Cited By ~ 7

Author(s):

Amy G. L. Nuttall ◽

Werner Velásquez ◽

Caroline S. Beardsmore ◽

Erol A. Gaillard

Keyword(s):

Early Stage ◽

Airway Disease ◽

Small Airway ◽

Small Airways ◽

Lung Clearance ◽

Additional Information ◽

Small Airway Disease ◽

Lung Clearance Index ◽

Children With Asthma ◽

Ventilation Heterogeneity

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.

Download Full-text

Modelling resistance and reactance with heterogeneous airway narrowing in mild to severe asthma

Canadian Journal of Physiology and Pharmacology ◽

10.1139/cjpp-2014-0436 ◽

2015 ◽

Vol 93 (3) ◽

pp. 207-214 ◽

Cited By ~ 18

Author(s):

Swati A. Bhatawadekar ◽

Del Leary ◽

Geoffrey N. Maksym

Keyword(s):

Frequency Dependence ◽

Severe Asthma ◽

Respiratory System ◽

Upper Airway ◽

Airway Disease ◽

Small Airway ◽

Small Airways ◽

Airway Narrowing ◽

Ventilation Heterogeneity

Ventilation heterogeneity is an important marker of small airway dysfunction in asthma. The frequency dependence of respiratory system resistance (Rrs) from oscillometry is used as a measure of this heterogeneity. However, this has not been quantitatively assessed or compared with other outcomes from oscillometry, including respiratory system reactance (Xrs) and the associated elastance (Ers). Here, we used a multibranch model of the human lung, including an upper airway shunt, to match previously reported respiratory mechanics in mild to severe asthma. We imposed heterogeneity by narrowing a proportion of the peripheral airways to account for patient Ers at 5 Hz, and then narrowed central airways to account for the remaining Rrs at 18 Hz. The model required >75% of the small airways to be occluded to reproduce severe asthma. While the model produced frequency dependence in Rrs, it was upward-shifted below 5 Hz compared with in-vivo results, indicating that other factors, including more distributed airway narrowing or central airway wall compliance, are required. However, Ers quantitatively reflected the imposed heterogeneity better than the frequency dependence of Rrs, independent of the frequency range for the estimation, and thus was a more robust measure of small-airway function. Thus, Ers appears to have greater potential as a clinical measure of early small-airway disease in asthma.

Download Full-text

Relationships between the lung clearance index and conductive and acinar ventilation heterogeneity

Journal of Applied Physiology ◽

10.1152/japplphysiol.01221.2011 ◽

2012 ◽

Vol 112 (5) ◽

pp. 782-790 ◽

Cited By ~ 44

Author(s):

Sylvia Verbanck ◽

Manuel Paiva ◽

Daniel Schuermans ◽

Shane Hanon ◽

Walter Vincken ◽

...

Keyword(s):

Compartment Model ◽

Normal Subjects ◽

Bronchial Tree ◽

Small Airways ◽

Lung Clearance ◽

Lung Clearance Index ◽

Asthma Patients ◽

Ventilation Heterogeneity ◽

Multiple Breath Washout ◽

Washout Curves

The lung clearance index (LCI) derived from a multiple breath washout test has regained considerable popularity in recent years, alternatively being promoted as an early detection tool or a marker of small airways function. In this study, we systematically investigated the link between LCI and indexes of acinar and conductive airways ventilation heterogeneity (Sacin, Scond) to assess potential contributions from both lung zones. Relationships were examined in 55 normal subjects after provocation, where only Scond is known to be markedly increased, and in 55 asthma patients after bronchodilation, in whom both Scond and Sacin ranged between normal and abnormal. LCI was correlated to Scond in both groups ( R = 0.37–0.43; P < 0.01 for both); in the asthma group, LCI was also tightly correlated to Sacin ( R = 0.70; P < 0.001). Potential mechanisms operational at various levels of the bronchial tree were identified by considering washout curvilinearity in addition to LCI to distinguish specific ventilation and dead space effects (also illustrated by simple 2-compartment model simulations). Although the asthma data clearly demonstrate that LCI can reflect very peripheral ventilation heterogeneities, the normal provocation data also convincingly show that LCI increases may be the exclusive result of far more proximal ventilation heterogeneities. Because LCI potentially includes heterogeneities at all length scales, it is suggested that ventilation imaging in combination with LCI measurement at the mouth could identify the scale of relevant ventilation heterogeneities. In the meantime, interpretations of LCI results in the clinic based on washout curves collected at the mouth should be handled with caution.

Download Full-text

The validity of shortened multiple breath washout testing using sulphur hexafluoride in the assessment of patients with COPD

ERJ Open Research ◽

10.1183/23120541.00379-2020 ◽

2021 ◽

pp. 00379-2020

Author(s):

Neil Greening ◽

John Owers-Bradley ◽

Sally Singh ◽

Salman Siddiqui

Keyword(s):

Chronic Obstructive ◽

Small Airways ◽

Clinical Use ◽

Clinical Markers ◽

Sulphur Hexafluoride ◽

Obstructive Pulmonary Disease ◽

Lung Clearance Index ◽

Ventilation Heterogeneity ◽

Multiple Breath Washout ◽

End Tidal

IntroductionChronic Obstructive Pulmonary Disease (COPD) affects the small airways and is associated with ventilation heterogeneity. There is little data on the Multiple Breath Washout (MBW) in patients with COPD particularly the variability over eight weeks, using a shortened sulphur hexafluoride (SF6) washout. This work evaluated the repeatability of the LCI1/40 and LCI1/20 among subjects with COPD and compared to spirometry and clinical markers.MethodsThe MBW was performed on patients with COPD to determine ventilation heterogeneity globally (Lung Clearance Index (LCI)), at conductive (Scond) and acinar (Sacin) levels. The LCI was repeated in triplicate and measured at a traditional 1/40th washout and retrofitted to a shortened 1/20th end tidal SF6 concentration washout. Tests were repeated after 20 min and eight weeks to determine within and between visit repeatability and compared with spirometry.Results84 subjects were recruited to perform LCI and spirometry with 20 subjects performing the repeatability protocol. There were weak correlations between FEV1 percent predicted and LCI1/40th r=−0.311 (p=0.02), and LCI1/20th r=−0.40 (p<0.01). The LCI demonstrated excellent within and good between visit repeatability for both a 1/40th and 1/20th washout (ICC≥0.80). There was a statistically significant strong correlation between LCI1/40th and a shortened LCI1/20 0.86 (p<0.01).ConclusionsThe LCI is repeatable within and between visits. There are weak correlations with measures of spirometry. A shortened LCI1/20th starting concentration correlates highly with a 1/40th washout which may encourage clinical use.

Download Full-text