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piece methods. The main difference between these techniques is an increased flow of
Z2lmlstmin, and the adult technical studies revealed that with increasing flow there was a
decreasing level of exhaled NO obtained. In this case, an increase in flow of 52Vo led to a
reduction of exhaled NO of 407o.
The study was not designed to look at age-related differences in exhaled NO, as had been
suggested by Lundberg et al as occurring with possible development and pneumatisation of
the sinuses (Lundberg, Farkas-Szallasi et al. 1995). The children studied were in a nalrow age
range to try and standardise the results and to limit other extraneous effects. The age was
chosen as those likely to be able to do lung function tests and therefore complete the exhaled
No testing successfully. However the results in these 'normal' children were significantly
lower than the results obtained from the twelve healthy adults studied initially except for the
comparison of t-piece measurement in males. The children had mean exhaled No level
4g.6ppb compared to 84.8ppb in adults via direct measurement and mean NO 29'7ppb
compared to 41.2ppb in t-piece measurement. The boys had a mean exhaled NO of 43'lppb
(direct) and 25.6ppb (t-piece) compared to 71.7ppb (direct) and 33'2ppb (t-piece) of male
adults. The girls had a mean exhaled NO of 55.2ppb (direct) and 33.8ppb (t-piece) compared
to 92.4ppb (direct) and 50.7ppb (t-piece) of female adults. The differences werc more
significant for the direct than the t-piece technique. There was no difference within this close
two year age band, though it was noticeable that the nine year old children found it more
difficult to control expiration within the prescribed limits than the older children did' This
niurow and young age bracket was also chosen to try and enrol children that were prepubertal
following suggestions that exhaled No may vary through the menstrual cycle (Kharitonov'
Logan-sinclair et al. 1gg4). This ruled out a confounding factor if it was later discovered that
pubertal change had effects on exhaled No in either male or females, although, in fact' this
remains unknown. In both the children and the adults there was no significant difference in
exhaled NO between the genders.
There were significant differences between the duration of exhalation with the mean being
32.9 seconds for the children and 56.2 seconds for the adults in the direct measurements, and
2g.6 seconds for the children and 53.5 seconds for the adults in the t-piece measurements'
Three children had long exhalations of greater than 50 seconds for all of their direct method
exhalations and longer than 40 seconds for all the t-piece method exhalations and all had the
higher levels of peak coz measured. Interestingly, these three had swimming training and
were on representative teams either at the school and/or swim clubs'
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