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a mean value of 32.9 seconds for the direct method (SD 1 !.4, range 15'8-65'8s) and a mean
value of 28.6 seconds for the t-piece method (SD 7.8, range 14'8-48s)' The mouthpiece was
standardised at 4.OmmHg in both techniques and the flow to 225mlslmin in the t-piece
method by voluntary control using visual feedback to the children. There was still some
variation around this depending on how successful the children were at maintaining the
pressure and flow as requested during a slow exhalation from total lung capacity which is
shown in Table 8.1.
Table 8.1: Coefficients of variation of peak NO, peak COzand mouth pressure measurements made
by both the direct and t-piece systems, and of flow made by the t-piece system
Direct method:
Peak NO in PPb
CQ2"/" totalgases
T-piece method:
Peak NO in pPb
CO2"/o totalgases
Mouth pressure in
Flow in mls/min
comparisons were made within this group of children of other factors that could result in
ainvay inflammation which may give higher results of exhaled No. Regarding a personal
history of atopy; the question sent home to the parents was:
Has he/she ever had eczema?
Has he/she ever had hay fever?
25.9
0.44
22.4
29.9
0.44
12.5
14
Yes/l'{o
Yes/No
Does he/she have eczemalha.yfever now? YesA'{o
2.6-67.4
0.41-0.81
4.5-57.0
0.5-65
0.41-0.81
2.9-36.1
1.8-30.3
There were eleven children that had a personal past or current history of allergic rhinitis
compared to 28 children who did not. At the time of testing none had current nasal symptoms
but three did have current eczema and were using appropriate topical creams including
hydrocortisone cream. There was no significant difference in the exhaled No levels in the
atopic children at 34.5ppb (sD 11.8) compared to non-atopic children at 45'6ppb (sD 38'5)
via the direct method or via the t-piece method measured at29'6ppb (SD 24) versus 24'8ppb
(SD 26.2) respectively. We also looked at whether family history of atopy had any effect on
the exhaled No levels in the children. The question sent home to the families was:
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