Biomedical Engineering Reference
In-Depth Information
Figure 6
Airway mucus hypersecretion in COPD. Mucus occupying ratio (MOR)
is significantly greater in both central and distal airways of patients who die with a
diagnosis of chronic bronchitis compared with those with emphysema or controls
without respiratory disease. L, luminal perimeter; Sb
1
, size of bronchus before com-
puter-based image analysis conversion to Sb
2
(Br, bronchial radius); S
m
, size of
stained area of mucus. Redrawn after 22.
morphologically normal. Gland size in COPD correlates with the amount of
luminal mucus and daily volume of sputum (25). Although not necessarily
causal, the latter observation suggests a strong relationship between gland
hypertrophy and mucus hypersecretion in COPD.
The above features of hypersecretion are not common to all COPD
patients. Not every patient expectorates, and there is overlap in gland size
with healthy nonsmokers, and also between sputum producers and nonpro-
ducers (24,26,28-30). Goblet cell hyperplasia is not noted in all patients
(22,27). Interestingly, although goblet cell hyperplasia is associated with
degree of airway inflammation, gland size is not (24). Thus, although
considered a general feature of COPD, mucus hypersecretion does not
characterize all patients.
The mucin composition of airway mucus may be abnormal in COPD.
Mucins in sputum are less acidic than normal (31), which may relate to
disease-related alterations in glycosylation. MUC5AC and a low charge
glycoform of MUC5B are the major mucin species in patients with COPD
(32-35). Intriguingly, the low charge glycoform appears to be relatively
increased above normal levels (36), a potentially significant observation that
requires confirmation, or otherwise, in a greater number of samples. It is
possible that the change in MUC5B glycoforms, coupled with the reduc-
