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Some of these studies, particularly the early studies, may have included subjects on
inhaled or oral corticosteroids and not differentiated them within the study groups.
NO may degrade within the mucus giving low levels reaching the airway lumen for
measurement.
Pseudomonas aeruginosa produces a pigment pyocinen which in vitro has been shown
to inactivate NO (Wanen,I-oi et al. 1990).
While the true reason is likely to be a combination of these factors, the obstruction to
diffusion of NO into the airway and trapping of NO within the mucus, probably plays the
major role. The low nasal NO level seems a consistent finding in this population, and in adults
oral NO also appears to be low, with a possible correlation between higher lung function and
higher NO levels.
9.11 Nitric oxide levels in bronchiectasis
An initial paper suggested both elevated levels exhaled NO and a correlation between this and
the chest CT scan score in 20 patients with bronchiectasis, but neither were seen in another 19
on IHCS treatment (Kharitonov, Wells et al. 1995). Subsequent papers have not confirmed
these findings in 16 (Ho, Innes et al. 1998), 3l (Horvath, Loukides et al' 2003) and 109
(Tsang, Irung et a\.2}}2)patients with bronchiectasis measured at a time of disease stability'
Those with pseudomonas aeruginosa infection (25 of 109) did have significantly lower levels
of exhaled NO although their sputum NO concentration was the same' There was no
correlation between the levels of exhaled No and FEVI, FVC or the number of bronchiectatic
lobes involved (Tsang, lrung et al. 2o02). similar to findings in cF, it is surprising not to
find elevated NO in such an inflammatory and infective disease. The mucus layer may well be
a barrier to detection of the production of NO, and in an inflamed environment the presence of
reactive oxygen species may result in interaction with this highly reactive molecule resulting
in effective removal of NO to form other compounds, such as perioxynitrite. The use of NO
here is likely to be as a screen in bronchiectasis - if low nasal No levels are obtained, then CF
and PCD testing must be undertaken.
g.l2 Nitric oxide levels in upper resoiratory tract infections
The effect that upper respiratory tract infections (URTI) have on exhaled NO levels has also
been studied. In 18 non-asthmatic adults during an URTI, increased exhaled NO levels to
315ppb were noted, decreasing to 87ppb during recovery at two to three weeks which became
similar to aged matched healthy controls (Kharitonov, Yates et al. 1995). When 79 COPD
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