Biomedical Engineering Reference
In-Depth Information
lumen size, in pulmonary muscular arteries (4-8) (Fig. 1). This enlargement
is apparent when comparing COPD patients with nonsmokers of similar age
(6), thereby ruling out a potential effect of aging (9). Intimal enlargement
occurs in arteries of different sizes, although it is more pronounced in small
arteries with an external diameter less than 500 mm (4,5).
Muscularization of small arterioles, which in normal conditions lack
a definite muscular layer, is another characteristic feature of pulmonary
vessels in patients with mild-to-moderate COPD. Morphometric studies
have shown an increased number of pulmonary muscular arteries with small
diameters (
<
200 mm) as compared with control subjects (10).
Changes in the media of pulmonary muscular arteries are less conspic-
uous and the majority of morphometric studies have failed to show differ-
ences in the thickness of the muscular layer when comparing patients with
mild-to-moderate COPD with control subjects (4-7) (Fig. 1). Therefore,
muscular hypertrophy is not a characteristic feature of pulmonary vascular
remodeling in mild COPD.
The degree of pulmonary vascular changes in mild-to-moderate
COPD correlates with the severity of emphysema and small airway abnorm-
alities (4,7,8).
B.
Severe COPD
In a classic post-mortem study conducted in patients with end-stage COPD
and cor pulmonale, Wilkinson et al. (11) showed prominent changes in
pulmonary muscular arteries consisting of an active deposition of longitudi-
nal muscle, fibrosis, and elastosis of the intima. In the arterioles, they
showed the development of a medial coat of circular smooth muscle,
bounded by a new elastic lamina. There was also deposition of longitudinal
muscle and fibrosis of the intima (11,12).
In another post-mortem study conducted in patients with COPD and
pulmonary hypertension who died while enrolled in the National Institutes
of Health Nocturnal Oxygen Therapy Trial (NOTT) study, Wright et al.
(12) showed a significant increase of intimal thickness in pulmonary muscular
arteries, compared with control subjects. The degree of intimal enlargement
was unrelated to the severity of pulmonary hypertension. The thickness of
the tunica media was slightly increased in patients with moderate-to-severe
pulmonary hypertension. Interestingly, the degree of pulmonary hypertension
was not related to changes in vascular structure since in patients with mild and
severe pulmonary hypertension intimal andmedial thickness were similar (12).
The study of lung tissue specimens obtained at lung volume reduction
surgery (LVRS) has provided the opportunity to evaluate pulmonary vessels
in patients with severe emphysema, who had functional measurements
obtained before surgery, thus allowing to establish structure-function corre-
lations in patients with advanced COPD. Yet, the morphologic assessment
is restricted to tissue in the vicinity of areas of emphysematous destruction.
