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is set at 5ppm (AIHA 1966) based on pulmonary oedema that developed in welders who had a
severe acute exposure to an estimated 9ppm of ozone (plus other pollutants) (Giel, Kleinfeld
et al. t957). Fifteen to 20ppm is lethal to animals in two hours, exposure to 50ppm for one
hour "would likely prove fatal to humans" (King 1963).
4.7 Chapter summary
This chapter has reviewed the possible compounds and methods that could be used to
determine the level of NO based around the known pathway of formation from L-arginine to
L-citrulline and NO, and the nitrogen compounds. The chemiluminescence technique was the
most appropriate for use in measuring exhaled NO in humans. This analysis is based on the
reaction of NO with ozone which produces light, and the light intensity has been shown to be
directly proportional to the concentration of NO in the sample. The chemiluminscence
technique appeared to be both appropriately sensitive and specific for NO for this purpose.
The chemiluminescent NO analysers available at that time had been developed to measure
NO in air pollution. The job now was to assess their use and examine what technical
alterations were required to enable measurement of NO in exhaled air in humans in a reliable
and reproducible way. This was needed before discussion as to what these levels meant, and
before a trial of measurement in children. Initial testing showed that the response time of the
analyser was too slow for our purpose initially, but a rerouting of the signal to a chart recorder
decreased the response time and meant that it was practical for use for the studies that follow.
Finally in this chapter, I have reviewed the toxicity of NO, NOz and ozone. Although I was
only going to be measuring NO in exhalate and therefore it was unlikely to reach high levels,
I was using NO calibration gases. NOz and ozone are the two gases created by this technique
so I wanted to also assess their toxicity, although I was planning to remove them immediately
by having them 'scrubbed' with a soda lime column and a charcoal column respectively.
The next chapter examines the chemiluminescent analyser Model 2107 @asibi
Environmental Corporation, Glendale, California, USA) in more detail, and the
commencement of the machine and subject methodology studies. What was known about
exhaled NO levels at the time of cornmencement of these studies in 1995 will also be
reviewed here.
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