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flow and to minimize nasal contamination. The tidal breathing method is less invasive and a
simpler collection method but it is not always possible to control flow or nasal NO
contamination. The most reproducible recordings have come from the second and third
exhalation phases, and with use of sedation in the infants. The results so far have
demonstrated a difference with gender, as suggested in some studies of older age groups, and
confirmed the effect of expiratory flow on NO. Antenatal effects include a decrease in infants
of smoking or caffeine ingesting mothers, though the effect of maternal (and patemal) atopy
has been either nil or resulted in an increased levels of NO. Higher levels of NO were
demonstrated in wheezy infants although the relation between this and those who develop
asthma versus those who have viral induced wheeze of infancy which is likely to disappear
between three and six years is not yet determined. The effect of a viral upper respiratory tract
infection is less consistent on NO levels. As with infant lung function, the measurement of
NO in this age group remains the premise of research groups and is not widely used in the
clinical arena.
9.18 Chapter summarv
Following early experiments throughout the 1990s, it was recognised that standardisation of
the method of measuring NO was required to allow better interpretation of results and
comparison between research groups. These began with a meeting in Stockholm in 1996 and
from 1997 to 2005 four documents were generated involving the ERS and the ATS detailing
standard procedures and then updating and refining these procedures as more data became
available (Kharitonov, Alving et al. 1997; American Thoracic Society and Association. 1999;
Baraldi, de Jongste et al.20O2l American Thoracic Society and European Respiratory Society
2005). What became increasingly apparent from very early in the research was the importance
of getting consistent and reproducible results. The most important factors to control were
expiratory flow and nasal contamination. Standard practices for single, tidal breathing,
reservoir collections and nasal measurements have been developed for both adults and
children. In addition, the use of different expiratory flows to assess NO from different lung
compartments has also been explored. This is important when wanting to demonstrate
inflammation in certain compartments in certain diseases, for example the airway
compartment in asthma and the alveolar compartment in interstitial lung diseases. In the latter
type of diseases, this technique should always be employed in the future to enable meaningful
results to be obtained.
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