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significantly between research groups, partly because of different techniques utilised. I-anz et
al reported a mean exhaled NO of 14ppb (+/- 2ppb) in seven children with single exhalations
from total lung capacity into a reservoir bag that was then fed through the NO analyser (lanz,
Irung et al. 1997). They also showed that there was no difference in the NO levels when re-
measured five days later (Lanz, I-eung et al. 1997). Using a similar method of slow exhalation
into a reservoir and then put through the analyser, Nelson et al reported a much lower mean
exhaled NO of 5.05ppb (+/- 0.4ppb) in 2I children (Nelson, Sears et al. 1997). Baraldi et al
showed that NO reached a steady plateau when measured during tidal breathing after one to
two minutes and reported mean levels of 5.4ppb in 16 children (Baraldi, Azzolin et ^1. 1997).
Lundberg et al also measured plateau oral exhaled NO levels with tidal breathing and reached
a similar figure of 4.8ppb (SD 1.1) in 19 children (Lundberg, Nordvall et al. 1996). Balfour-
Lynn et al measured NO from single exhalations taking the point of NO when the end tidal
COz reached a plateau in an attempt to compare alveolar levels for both oral and nasal
measurement. The 57 control children had a mean oral exhaled NO of 4.8 ppb (range l.l to
23ppb), and mean nasal NO of 1024 ppb (range 158 - 2502ppb) @alfour-Lynn, Laverty et al.
1996). Two studies measured controls across wide age ranges that incorporated an unknown
number of children. Dotch et al measured exhaled NO from single exhalations although the
response time of the analyser was not fast enough at 25 seconds for a 9OVo response rate to
measure one breath, so the subject was required to exhale four to five times into the analyser
via mouth inhalation and with nose clips in place. In 68 controls aged four to 34 years the
mean NO result was 3.0 ppb (+l-2.Sppb) by these single exhalations, with a minute ventilation
concentration of NO of 25 ppb (+l- 27 ppb) and direct nasal NO level of 96 ppb (+l- 47 ppb)
@otsch, Demirakca et al. 1996).
In another study, Grasemann measured NO by single exhalations to an analyser that had a 10
second response time. The mean exhaled NO level in 30 control subjects aged six to 37 years
was 9.1 ppb (+/- 3.6ppb). Lundberg et al measured the plateau NO signal by continuous
sampling from oral exhalation or nasal exhalation or by direct nasal measurement in 19
children. The mean oral level was 4.8ppb (SD 1.1), the mean nasal level was 2lppb (SD 9.1)
and the mean directly measured nasal level was 239ppb (SD 20) (Lundberg, Nordvall et al.
1996). Most of these researchers therefore reported absolute levels of exhaled NO that were
less than the results that I have reported from my studies. However I had elected to use single
exhalations measured immediately by the analysers, while these others used tidal breathing or
plateau measurements with or without a reservoir technique over several breaths.
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