Biomedical Engineering Reference
In-Depth Information
Thus, although the clinical, functional, and inflammatory characteris-
tics are usually markedly different in COPD and asthma, in clinical practice
the differential diagnosis between the two respiratory conditions may
become complex, particularly in the elderly or when there are overlapping
features. Indeed, it is easy to diagnose COPD in a 60-year-old life-long smo-
ker with dyspnea, chronic cough, and sputum, and fixed airflow limitation.
Similarly, it is quite easy to diagnose asthma in a young atopic nonsmoking
individual, with recurrent episodes of dyspnea, wheezing or chest tightness,
and variable and reversible airflow limitation. However, it might become
difficult to differentiate between COPD and asthma in adults over 60 with
confounding features, e.g., (1) smoking asthmatics, subjects with adult onset
asthma, (2) life-long nonsmokers who present with fixed airflow limitation
and no history of asthma, (3) smokers with a clear story of COPD but also
a significant degree of reversibility of the airflow limitation, (4) nonsmoking
asthmatics with fixed airflow limitation, (5) subjects who report both
diseases. In these cases, the differential diagnosis between COPD and
asthma may be difficult but nonetheless important, as the natural history
(Ref. 6) and the response to pharmacological treatment (Ref. 7) are different
in the two disease states.
Epidemiologic studies have shown that there is a significant overlap
between COPD and asthma. Subjects who report both diseases have lower
lung function and more respiratory symptoms than subjects with just one or
the other (8). Asthma may be associated with reduced lung function in up to
20% of adults (8), and significant reversibility of airflow limitation to ster-
oids have also been reported to occur in a significant proportion of subjects
with COPD and no history of atopy or asthma (9). Data from epidemiolo-
gical studies show that up to 12% of subjects with COPD are nonsmokers
(with a predominance of females) and there is evidence of increasing inci-
dence with increasing age (10-12). Over 20% of asthmatics are current smo-
kers and the 22-43% of adult asthmatics are exsmokers (13,14). Current
asthmatic smokers, compared with never smokers, have more severe asthma
symptoms, an accelerated decline in lung function, increase in hospitaliza-
tion rates for asthma, and increased mortality following a near fatal asthma
attack (15). Moreover, some data show that active smoking impairs the
efficacy of systemic and
=
or inhaled corticosteroid treatment in chronic
asthma (16,17).
II. ASTHMA WITH FIXED AIRFLOW LIMITATION
Although it has been reported that asthma may be associated with the devel-
opment of fixed airflow limitation (18) and respiratory failure (19), the nat-
ural history of asthma is not well defined. In particular, it is unclear whether
asthma is associated with progressive decline of lung function over time, and
