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measured over two 24 hour periods, there was a gender difference (again higher in boys than
girls) in the first assessment, but not in a second assessment (Napier and Turner 2005).
However other paediatric studies have not confirmed these associations; showing no
correlation observed between NO and height or spirometric data (Baraldi, Azzolin et al.
1999), and no correlation between nasal NO and body mass index (Struben, Wieringa et al.
2005). At the current time the reference ranges for 'normal' are given as one range, with no
gender correction.
9.7.2 Age
Early in the research literature, it was suggested that NO increased with age correlating to
pneumatisation of sinuses (see Figure 9.2) (Lundberg, Farkas-Szallasi et al. 1995). In over
650 healthy children aged4-17 years in three studies, exhaled NO significantly increased with
age in both off-line and online analyses (Franklin, Taplin et al. 1999; Kissoon, Duckworth et
al.2[f]l2; Buchvald, Baraldi et al. 2005). Nasal NO in 340 healthy children aged 6-17 years
also increased with age which would appear appropriate if it does relate to sinus development
(Struben, Wieringa et al. 2005). An increase of exhaled NO was confirmed in a younger age
goup of 2-5 year olds using tidal breathing (Avital, Uwyyed et al. 2003). One study also
demonstrated an increase between 1 and 24 hours of age in 13 healthy newborn infants
(Schedin, Norman et al. 1996). However, again findings have been inconsistent with no
correlation between age and exhaled NO seen in some groups (Baraldi, Azzolin et al. 1999;
Bartley, Fergusson et al. 1999). Despite the findings above, the current practice is to use one
range for normal values with no correction for the age of the subjects. It was however one of
our reasons for choosing a tight age bracket when measuring the exhaled NO in children in
the methodology study (see Chapter 8).
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