Little SA, MacLeod KJ, Chalmers GW, Love JG, McSharry C, Thomson NC. Am J Med. 2002;112:446–452
Purpose of the Study.
Some patients with chronic asthma develop irreversible airflow obstruction. The aim was to assess whether reported duration of asthma and induced sputum cell counts were associated with pulmonary function in patients with asthma who did not smoke.
Study Population and Methods.
Maximal forced expiratory volume in 1 second (FEV1) was determined after a steroid trial (oral prednisolone, 30 mg/day [n = 9 patients]; or inhaled fluticasone, 2000 μg/day [n = 5]; for 2 weeks) and 2.5 mg of nebulized albuterol. Asthma history was recorded with duration from first diagnosis. All subjects were nonsmokers, or were to have stopped smoking ≥5 years previously and smoked ≤5 pack-years (n = 12). Induced sputum was obtained from 59 subjects for analysis of airway cell counts.
Maximal FEV1 was inversely associated with asthma duration (r = −0.47; P < .0001), age (r = −0.40; P < .0001), and the proportion of sputum neutrophils (r(s) = −0.50; P = .00004). After adjusting for age, both duration of disease and sputum neutrophils were independently associated with maximal FEV1. Neutrophil activation, as measured by sputum myeloperoxidase levels, was positively associated with the proportion of sputum neutrophils (r(s) = 0.45; P = .0004) and inversely associated with maximal FEV1 (r(s) = −0.59; P < .0001).
Long disease duration may be a predisposing factor for the development of irreversible airflow obstruction in patients with chronic asthma. The negative associations of sputum neutrophil count and activation with maximal FEV1 suggest that neutrophils may be involved in the pathophysiology of irreversible airflow obstruction in asthma.
Of course, one doesn’t know if the neutrophils were the cause or the result of long-standing airways obstruction. Nonetheless, the study reminds us that many adults with long-standing asthma may develop irreversible airflow obstruction over time. When that happens, I always worry that some other cardiopulmonary process is going on and start ordering all sorts of expensive tests. For those interested in this subject, the article is accompanied by a thoughtful editorial (Am J Med. 2002;112:498–500).