Biomedical Engineering Reference
In-Depth Information
recoil and to have little relation to peripheral airway inflammation, as
supported by the correlation between reduced expiratory flow and increased
compliance observed in this form of emphysema (62,63,68).
Only a few studies attempted to correlate the pathological abnormal-
ities with the degree of airflow obstruction in COPD. The largest study, per-
formed by Nagai et al. (69), showed that subjects with severe COPD had
both emphysema and peripheral airway abnormalities. Although the relative
contribution of each of these pathologic lesions to the development of air-
flow obstruction was difficult to establish, the contribution of each may vary
according to the stage of the disease. Bronchiolar abnormalities may reveal
their contribution to chronic airflow obstruction only when COPD is mild.
When the disease becomes severe, loss of elastic recoil assumes overwhelm-
ing importance and may mask the effects of bronchiolar disease on causing
airflow obstruction (70).
In both centriacinar and panacinar emphysema, the destructive pro-
cess can be detected microscopically in the alveolar walls of smokers even
when there is no evidence of airspaces enlargement on gross examination.
Several methods have been designed to microscopically quantify emphy-
sema including the mean linear intercept and the destructive index (71).
Both allow an early identification of the disease, before macroscopic emphy-
sema is evident. The functional significance of such early destruction is
demonstrated by the positive correlation observed in smokers between
destructive index and both airflow obstruction and loss of elastic recoil of
the lung.
Since emphysema is defined pathologically, traditionally the presence
and extent of emphysema have been determined by macroscopic or by
microscopic assessment of lung specimens (72). However, these techniques
are time consuming and, more importantly, can hardly be performed in par-
tial lung resections and therefore in living patients. During the last few
years, it has become increasingly clear that high-resolution computed tomo-
graphy (HRCT) is an accurate imaging method for diagnosing emphysema
in vivo (73). Indeed, pioneer studies have shown that the extent of emphy-
sema assessed on HRCT scan correlates significantly with the extent of
emphysema assessed on macroscopic lung sections (74-78). A good correla-
tion has been reported also between HRCT emphysema assessment and
destructive index (76). More recently, Gevenois et al. compared transversal
CT slice and transversal anatomical lung slices showing that both macro-
scopic (79) and microscopic (80) emphysema are well quantified by CT in
smokers (81). These studies show that CT scanning represents a significant
advance in the ability to identify early emphysema in life and to follow its
progression, thus allowing pathogenesis to be better understood and the
effects of treatment to be determined (82). Nevertheless, as pointed out by
Madani et al., this technique is not yet standardized and further studies
are needed (73).
