Biomedical Engineering Reference
In-Depth Information
long subclinical course before they became symptomatic. It also led to the
hypothesis that small airways were the lungs quiet zone where disease might
be detected and reversed before serious airway obstruction occurred.
Although tests were developed that could detect functional abnormalities
in the small airways (10) they are no longer used in epidemiological studies
because the abnormalities they detect are present in most smokers and do
not predict the minority that will go on to develop COPD (11).
Figure 3 summarizes a classic study by Fletcher et al. (11) who made
longitudinal measurements of lung function on a group of working men
living in London. The lower curved line shows the rapid decline in lung
function experienced by a minority of approximately 15% of the cigarette
smoking population. The upper curved line represents the minimal decline
observed in nonsmokers and the middle two lines represent the decline in
FEV
1
observed in the majority of the smoking population that is less suscep-
tible to the cigarette smoking habit. The horizontal lines represent the five
stages of severity of COPD recommended by Global initiative on obstructive
lung disease (12). Class 0 consists of persons that have normal lung function
with respect to these tests but are at risk for COPD either because of their
smoking history or the presence of symptoms. Those where FEV
1
remains
in the normal range above 80% of the predicted value but the FEV
1
=
FVC
falls below 70% are assigned to the mild disease (Gold Stage 1). In moderate
COPD (GOLD-2) the FEV
1
ranges from 80% to 50%, severe disease
(GOLD-3) from 50% to 30%, and very severe (GOLD-4) below 30% of
the predicted value.
Figure 3
Shows the rate of decline in FEV
1
of men followed longitudinally by
Fletcher et al. (see Ref. 15) where a subgroup of heavy smokers lost FEV
1
very
rapidly. The horizontal lines indicate the boundaries of the GOLD classification of
COPD severity (see text and Ref. 12).
