Biomedical Engineering Reference
In-Depth Information
These data showed that the natural history of asthma is more favorable than
COPD once fixed chronic airflow obstruction has occurred.
A pivotal multicenter trial was conducted by Kerstjens et al. (7) who
compared the response to bronchodilators (terbutaline or ipratropium bro-
mide) or corticosteroid treatment in 274 patients with airways hyperrespon-
siveness and airflow limitation who were 18-60 years old. The 56% of
patients had allergies and the mean FEV
1
was 64% of the predicted value.
The mean FEV
1
increased by 10.3% of the predicted value in the corticoster-
oid group within 3 months and remained stable thereafter, whereas it did
not change in the other two groups. In the corticosteroid group, patients
who did not smoke, who had allergies, or who were
<
40 years old benefited
more from their treatment than did those who smoked, did not have aller-
gies, or were over 40. This study suggested that the addition of an inhaled
corticosteroid, but not of an additional bronchodilator (inhaled anticholi-
nergic agent) to maintenance treatment with a beta 2-agonist (terbutaline)
substantially reduced airways obstruction, but only in patients with a
history of allergy and
=
or asthma.
III. PATHOPHYSIOLOGY
A. COPD
In COPD, the structural changes occurring in both the large and small
airways, and in the lung parenchyma may be related to the characteristic
clinical manifestations and lung function changes of the disease, e.g. symp-
toms (i.e. chronic cough and sputum production), airflow limitation, gas-
exchange abnormalities, pulmonary hypertension, and cor pulmonale (2).
Inflammation of the submucosal glands and hyperplasia of goblet cells
may contribute to symptoms, such as chronic sputum production, although
these pathological abnormalities are not present in all patients with chronic
sputum and may be present in subjects without symptoms. The various
pathological changes in the central airways responsible for the symptoms
of chronic cough and sputum production may continue to be present
throughout the course of the disease. Thus, these pathological changes
may be present either on their own or in combination with the changes in
the peripheral airways and lung parenchyma described below.
Fixed or poorly reversible expiratory airflow limitation is the hallmark
functional abnormality of COPD. Several pathological characteristics may
contribute to airflow limitation. Airway remodeling and emphysema are
most likely responsible for the fixed, poorly reversible component of airflow
limitation, whereas airway smooth-muscle contraction, airway inflamma-
tion, and intraluminal accumulation of mucus and plasma exudate may
be responsible for the small part of airflow limitation that is still reversible
either spontaneously or with treatment (1) (Table 1).
