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Chapter 6: Methodological studies of exhaled nitric oxide in healthy adult subjects:
6.1 Introduction
direct versus t-piece testing
So far, I have examined why a marker of airway inflammation that was easy to measure,
particularly in terms of being non-invasive, would be useful. I have outlined the developing
knowledge on NO as a physiological agent and inflammatory marker. The previous chapters
then explored how NO could be measured by chemiluminscence and presented data on
adapting an appropriate analyser with our own initial methodology testing. In this chapter, I
will very briefly review NO in the lung, the literature on exhaled NO available to me at the
beginning of my research, and present the methodology experiments themselves. The first
experiment, which will be presented in detail in this chapter, was to assess the ability to
measure NO from exhalation in adults and to compare NO, CO2, mouth pressure and flow
traces using two methods; direct to analyser and side arm sampling systems. The following
chapter will detail further experiments designed to examine a number of technical factors to
assess whether they alter the levels of exhaled NO obtained. These investigations were in
response to the newly presented and published literature in this area where, although the
conclusions were similar from different research groups regarding NO results in different
populations, it remained curious that the absolute levels of NO being documented were very
different. How the results from these experiments then fit into subsequent research, current
literature and new discoveries are detailed in Chapter 9.
6.2 Nitric oxide and the nitric oxide synthases in the lung
From the literature presented in Chapter 2.2 'Nitric oxide in biological systems', and in
Chapter 3.4 'Nitric oxide synthase isoenzymes', it was clear that NO and the NOS enzymes
were widespread throughout human organ systems. In the lung, NO has four major roles -
vasodilator, bronchodilator, neurotransmitter for the NANC neryes and as an immune and
inflammatory mediator. By the time of this research all three isoforms of the enzyme had been
detected in the human respiratory tract @arnes and Belvisi t993; Jorens, Vermeire et al.
1993; Marsden, Heng et al. 1993; Moncada and Higgs 1993; Singh and Evans 1997).
localisation of NOS in lung tissue was demonstrated by immunohistochemical labelling
using both polyclonal and monoclonal NOS antibodies @redt, Hwang et al. 1991; Schmidt,
Gagne et al. 1992; Hamid, Springall et al. 1993; Hattori, Kosuga et al. 1993; Kobzik, Bredt et
al. 1993; Forstermann, Closs et al. 1994; Rengasamy, Xue et al. 1994; Kawai, Bloch et al.
t995; Ambalavanan, Mariani et al. 1999). The detection of NOS within the respiratory tree
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