title: Techniques for assessing small airways function: Possible applications in asthma and COPD.
abstract: In recent years special interest has been expressed for the contribution of small airways in the pathophysiology, clinical manifestations and treatment of asthma and COPD. Small airways contribute little to the total respiratory resistance so that extensive damage of small airways may occur before the appearance of any symptoms, and this is the reason why they are characterized as the "silent zone" of airways. Furthermore, the peripheral localization of the small airways and their small diameter constitutes difficult their direct assessment. Thus, they are usually studied indirectly, taking advantage of the effects of their obstruction, such as premature closure, air trapping, heterogeneity of ventilation, and lung volume dependence of airflow limitation. Today, several heterogeneous methods for the assessment of small airways are available. These can be either functional (spirometry, plethysmography, resistance measurements, nitrogen washout, alveolar nitric oxide, frequency dependence of compliance, flow-volume curves breathing mixture of helium-oxygen) or imaging (mainly through high resolution computed tomography). The above-mentioned methods are summarized in Table 1. However, no method is currently considered as the "gold standard" and it seems that combinations of tests are needed. Furthermore, it is not clear whether the small airways are affected in all patients with asthma or COPD and their clinical significance remains under investigation. Well-designed future studies with large numbers of patients are expected to reveal which of the methods for assessing the small airways is the most accurate, reliable and reproducible, for which patients, and which can be used for the evaluation of the effects of treatment.
authors.affiliation: Pulmonary Department, 424 General Army Hospital, Thessaloniki, Greece.
authors.forename: K
authors.initials: K
authors.lastname: Konstantinos Katsoulis
authors.affiliation: Private Practice, Karditsa, Greece.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Kostikas
authors.affiliation: Pulmonary Department, Aristotle University, Thessaloniki, Greece. Electronic address: kontak@auth.gr.
authors.forename: Theodore
authors.initials: T
authors.lastname: Kontakiotis
mesh_terms: D000403:Airway Resistance / Q000502:physiology; D001249:Asthma / Q000000981:diagnostic imaging / Q000503:physiopathology*; D003011:Closing Volume / Q000502:physiology; D005260:Female; D005652:Functional Residual Capacity / Q000502:physiology; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D009991:Oscillometry / Q000379:methods; D010991:Plethysmography; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging / Q000503:physiopathology*; D012119:Respiration; D012129:Respiratory Function Tests / Q000379:methods; D012137:Respiratory System / Q000000981:diagnostic imaging / Q000503:physiopathology*; D013147:Spirometry / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D009569:Nitric Oxide; D009584:Nitrogen
keywords: Alveolar nitric oxide; Dynamic compliance; Helium–oxygen mixture; Nitrogen washout; Oscillometry; Plethysmography