Biomedical Engineering Reference
In-Depth Information
thus whether (1) asthmatics indeed develop fixed airflow limitation, and if
so, (2) whether the pathological basis of fixed airflow limitation occurring
in asthmatics is similar to the development of fixed airflow limitation occur-
ring in COPD.
Recent data from a longitudinal epidemiological study conducted in
the general population, the Copenhagen City Heart Study, have recently
provided an answer to this important question (3). Data were analyzed in
terms of changes over time in the forced expiratory volume in one second
(FEV
1
) in adults with self-reported asthma and adults without asthma (3).
The study, conducted between 1976 and 1994, evaluated measurements of
lung function from 17,506 subjects, of whom 1095 had asthma, over a 15-
year period. The decline in FEV
1
among subjects with asthma was greater
than among those without the disease. Among both men and women, and
among both smokers and nonsmokers, subjects with asthma had greater
declines in FEV
1
over time than those without asthma. This study demon-
strated that in a sample of the general population, people who identified
themselves as having asthma have substantially greater declines in FEV
1
over
time than those who do not (3), suggesting that asthma, similarly to COPD,
may indeed be associated with the development of fixed airflow limitation
albeit at a lesser extent. Thus, asthma similarly to COPD, but obviously
through different mechanisms, may indeed be associated with an increased
decline of lung function that can cause fixed airflow limitation (3,20,21).
Patients with fixed airflow limitation are often grouped under the gen-
eral heading of COPD, and some international guidelines (22) recommend
classifying asthma with fixed airflow limitation as COPD. However,
although asthmatic patients with fixed airflow limitation are often diagnosed
as COPD, the differential diagnosis between asthma and COPD in patients
with fixed airflow limitation may be important as the natural history (6) as
well as the response to treatment (7) are different, depending on whether
fixed airflow limitation is due to asthma or COPD. The course and prog-
nosis in subjects selected from the general population having chronic airflow
obstruction (FEVI
<
60% predicted) at the time of their enrollment was
analyzed in a longitudinal epidemiological study (6). Mortality and the rate
of change in lung function were analyzed in relation to the initial clinical
characteristics of the subjects. Subjects with symptoms and signs of asthma
had a higher survival rate and a much lower rate of decline in pulmonary
function than subjects with clinical characteristics compatible with an
emphysematous form of COPD. The 10-year mortality among nonatopic
smokers without a history of asthma was close to 60%, whereas it was only
15% in atopic subjects or nonsmokers with known asthma. The mean over-
all rate of decline in FEV
1
was 70mL per year in COPD patients, but less
than 5mL per year in subjects with symptoms and signs of asthma. Patients
who did not clearly fit into either COPD neither asthmatic subjects had
intermediate values for survival and decline in pulmonary function (6).
