What Is New In Small Airways Research
Ves Dimov, MD
Allergist/Immunologist at Cleveland Clinic
Clinical Associate Professor
FAU Charles E. Schmidt College of Medicine
Small airways disease is highly prevalent in asthma (50-60%), even in patients with milder disease
This systematic literature review co-authored by PJ Barnes evaluated the prevalence of small airways disease in adult asthma. Small airways dysfunction and inflammation contribute to clinical impact of asthma, yet conventional methods of assessing airways function cannot reliably evaluate its presence.
15 publications were identified determining the prevalence of small airways disease in asthma. Methods of assessments included:
- impulse oscillometry
- body plethysmography
- multiple-breath nitrogen washout
- high-resolution computed tomography
The prevalence of small airways disease was 50-60% among patients with asthma. Small airways disease was present across all asthma severities, with evidence of distal airway disease even in the absence of proximal airway obstruction.
Source: Usmani OS, Singh D, Spinola M, Bizzi A, Barnes PJ. The prevalence of small airways disease in adult asthma: A systematic literature review. Respiratory Medicine 2016; 116:19-27. (doi:10.1016/j.rmed.2016.05.006)
Image source: Wikipedia, Flow-volume loop, public domain.
Significant inflammation in the small airways is found in all severities of asthma
Asthma is an inflammatory condition of both the small and large airways. Small airways have gained increasing attention as studies have shown significant inflammation in the small airways in all severities of asthma. Noninvasive methods to reliably measure small airways are being actively explored. Recent changes in asthma inhalers have led to alterations in drug formulations and development of extrafine particles that may improve delivery to the distal airways.
Source: Finkas LK, Martin R. Role of Small Airways in Asthma. Immunology and Allergy Clinics of North America 2016; 36(3): 473-482. (doi:10.1016/j.iac.2016.03.009)
FeNO combined with impulse oscillometry can better evaluate small airway function in asthmatic patients
This study investigated the relation between fractional exhaled nitric oxide (FeNO), impulse oscillometry (IOS) and small airway function in 140 asthmatic patients (71 of them had small airway dysfunction).
Levels of FeNO, reactance area (AX), resonant frequency (Fres) and blood eosinophils were increased in small airway dysfunction group. FeNO, AX and Fres correlated with FEF25-75% values. A receiver operating characteristic (ROC) analysis showed that the combination of FeNO, AX and Fres had a greater area under the ROC curve (AUC) than each of them individually.
FeNO combined with IOS can better evaluate the small airway function in asthmatic patients.
References: Liu L, Liu W, Liu C, Wang D, Zhao J et al. Study on small airway function in asthmatics with fractional exhaled nitric oxide and impulse oscillometry. Clinical Respiratory Journal 2016; published online ahead of print, September 28. (doi:10.1111/crj.12548)