Published Online: April 4, 2013
Until recently the small airways have been labelled as the ‘silent zone’ of the lung, due in part to a lack of good measurement tools. The development of techniques measuring airway mechanics and ventilatory heterogeneity of the lung periphery, including Multiple Breath Nitrogen Washout (MBW) and the Forced Oscillation Technique (FOT), have been of great value in characterising small airway function so that increasing evidence implicates the small airways in common respiratory conditions such as asthma and COPD.
In the current issue of The Journal of Allergy and Clinical Immunology (JACI), Thompson et al use the MBW technique to measure the efficiency of gas mixing in the small proximal airways and the very peripheral acinar airways in patients who were admitted to hospital for an exacerbation of asthma and patients with stable asthma. In the patients with an exacerbation of asthma, they also reviewed a subgroup of these patients after intensive treatment with oral corticosteroids. The researchers performed further analysis on all subjects looking for an association between measures of gas mixing from the MBW and treatment requirement as defined by the GINA step criteria.
The researchers demonstrated in all asthma patients studied that gas mixing inefficiency originating in the acinar zone of the lung is a major contributor to airflow obstruction. Importantly, asthma severity as measured by treatment requirement was more closely related to inefficiency of gas mixing occurring in the acinus rather than the small conducting airways. Finally, the efficiency of gas mixing within the acinus of patients with acute severe asthma was partly reversible following intensive (oral) corticosteroid treatment.
The researchers’ finding that the major determinant of asthma severity is located in the acinar lung zone is novel and important. Furthermore, the findings by Thompson et al highlight the importance of targeting steroid or alternative therapies (potentially small particle inhaled corticosteroids) to this zone in patients with asthma.
The Journal of Allergy and Clinical Immunology (JACI) is the official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.