Dr. Sally E. Wenzel, MD, editor of the American Thoracic Society CME Monograph Series (May, 2000) emphasizes that the traditional definition of asthma as "a chronic disturbance of the contractile function of airway smooth muscle" is now "a chronic inflammatory condition of the airways". In the following report, Dr. Richard J. Martin presents evidence that the majority of pulmonary inflammation associated with asthma in humans is found in the alveolar region and small airways.

Asthma is defined by three characteristics: reversible airway obstruction, bronchial hyper-responsiveness, and inflammation. Relatively new information on the distribution of asthma-associated inflammation in humans is available due to technical advances in bronchoscopy procedures allowing smaller distal airways to be observed and measured. Previously all data were from studies of the proximal large and medium sized airways.

By measuring peripheral airway resistance in humans, it is known that mild asymptomatic subjects have a significant increase in peripheral airway resistance in spite of near normal lung function. It is possible to examine the alveolar region with the use of transbronchial biopsies. These biopsies reveal a great influx of inflammatory cells into the alveolar region of asthmatics; many of the inflammatory cells are eosinophils and degranulated eosinophils. Since asthma often worsens during the night, studies of asthmatics during the day versus night are performed. There appears to be more alveolar region inflammation during the night and a corresponding decrease in lung function in nocturnal asthmatics.

The clinical implications of this new knowledge concerning the location of inflammation in asthmatics relate to current treatments for asthma. Most of these treatments involve the use of metered dose inhalers to deliver steroids or other drugs. Currently only 10 to 15% of the total dose delivered by a MDI filled with steroid is delivered to the small airways and alveolar area. In addition, inhaled steroids only improve lung function by 15% in asthmatics. Often normal lung function is not regained.

The author urges the development of better, more efficient methods of delivery of aerosol to the peripheral lung for more effective treatment of asthma.

An improved treatment method is presented in another article in this monograph series¹.  In this study, the authors demonstrate that a steroid aerosol of extra-fine particles (MMAD ~1.1 um) penetrates the peripheral lung more efficiently than does a traditional aerosol (3.5 -4.0 um).

1 - Tashkin, D. P., Golden, J.G., Kleerup, E.C., May 2000. Evaluation of Small Airways and the Impact of Inhaled Steroids - Size Does Matter. American Thoracic Society Continuing Medical Education Series Monograph Series. Pgs. 7-15.

By: Susan G. Shami, ScD