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ecruit blood vessels in the lung. Studies have also suggested that a normal NO reading at the
beginning of exercise predicted that no exercise-induced bronchospasm occurred.
Low nasal NO appears to be helpful in screening for PCD and possibly CF. It is particularly
important to measure this in children with established bronchiectasis and detecting a low NO
level early in assessment for recurrent respiratory illnesses would be additionally beneficial
and would indicate that these diseases must be investigated and excluded. The low NO levels
seen in PCD remain unexplained, while those in CF and other conditions such as sinusitis
would appear to be secondary to sinus obstruction. Oral NO levels are also low in PCD, but
the nasal NO measurements (using a cut point of 250ppb) have minimal overlap with normal
children. Oral NO levels become low in CF with age and disease progression, probably with
entrapment of NO within thick mucus and therefore likely to interact with other compounds,
so the NO does not reach the air to be exhaled. NO levels are increased in acute infections in
both normal subjects and those with COPD, and increase during times of higher pollution and
also associated with respiratory symptoms. However 'smoking' remains a confounding factor
here -
again rendering the measurement of NO as useless. In interstitial lung disease, levels of
NO co-relate with severity, in particular that assessed by the diffusion co-efficient, but only
when measured in the alveolar compartment. The measurement of NO has been undertaken in
infants and here while the parameters are still being worked through, it appears that the results
are already low in those with PCD and CF, and high in children with wheeze, though it is still
to be clarified whether this will result in detecting asthma versus infant viral associated
wheeze, and whether it matters, as it may just detect disease that will respond to steroids.
The advantages of using NO measurement rather than (or in addition to) other parameters is
obvious. It is much easier to perform, especially in children, than lung function testing or
induced sputum for eosinophils or any of the blood measurements such as total IgE. In
addition it is quicker, with immediate results, and potentially can be done away off hospital
site. While it still needs an understanding of the test and qualified personnel, it can be taught
and undertaken more easily than the other investigations.
So where do I see it as cunently being MOST useful:
l. Nasal (and oral) measurement as a screen for PCD. If nasal levels are low - ensure
investigation for PCD and CF are carried out. While we do have a newborn screening
for CF here in New Zealand,87o of children are not detected.
2. As confirmation of asthma in steroid natve patients - when NO levels should be high.
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