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Chapter 7: Methodological studies of exhaled nitric oxide in healthy adult subjects:
7.t Introduction
investigating test Parameters
The previous chapter described the commencement of the methodological studies into exhaled
NO in adult volunteers. The first investigation was the measurement and comparison of NO
and COz in single exhalations by two methods; direct to analyser and via t-piece sampling
systems. In both methods the results and patterns of NO and COz could be determined, as well
as expiratory mouth pressure measurement and, in the t-piece system, expiratory flow could
also be recorded. This was an attempt to answer the question as to whether NO and COz came
from the same areas within the lung. This experiment also demonstrated a significant
difference in the peak exhaled NO levels with an almost halving of the NO result when
moving from the direct to t-piece measurements with no corresponding reduction seen in the
peak CO2 levels. The main change between these two techniques appeared to be an increase
in the expiratory flow which was required for the t-piece sampling. I have already noted in the
previous chapter (Section 6.4) the different levels of NO reported by different researchers
despite investigating similar population groups (healthy controls, asthmatics, smokers) and
summarised these in Table 6.1. I thought it was vital to understand which parameters when
altered gave different exhaled NO results. This was needed to be able to recommend
standardised procedures so that better interpretation of results would be possible both between
different research groups and in comparisons of results in health and disease.
As mentioned in Section 6.4, the aims in designing the methodological experiments were to
answer two main questions Posed:
l. Were NO and CO2 produced from the same regions within the lung?
2. Which technical factors during measurements led to changes in the exhaled NO results?
The results from the direct versus t-piece analysis suggested that the exhalation patterns seen
were different between the gases. While it was known that COz was of alveolar origin, the
pattern of NO exhalation suggested that it came from a more proximal source such as the
airways. So I felt that we had answered the first question. The experiments detailed
throughout this chapter were to answer the second question' The parameters chosen to
examine, by changing each one alone and maintaining an otherwise standardised procedure,
were:
o The effect of expiratory flow
suggested by discrePancies in
- an effect of flow altering the level of NO had been
the published literature summarised in Section 6.3 'The
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