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led to an increased water content that decreased measured NO levels, though this could be
minimised by exhaling through a water absorber into the reservoir bags (Steerenberg,
Nierkens et al. 2000). NO online measurement correlated well with NO measured via a
balloon technique (mylar foil) when measured immediately during times of low air pollution
and high pollution days (van Amsterdam, Verlaan et al. 1999). Another group disagreed and
showed that the online measurement was higher than the mylar bag reservoir results when
both were measured immediately (Silkoff, Stevens et al. 1999), though the offline
measurements were similar to the end expiratory online measurements (Jobsis, Schellekens et
al. 2001). NO concentration in the mylar bag was also shown to actually increase at24 and48
hours after collection (Silkoff, Stevens et al. 1999). When the first European Respiratory
Society Task Force (ERSTF) recommendations were published regarding the measurement of
exhaled air, they recommended the online technique of measurement (Kharitonov, Alving et
al. 1997).In some initial testing we did, teflon and "wine cask bags" (which are mylar foil
bags) did not seem to absorb NO, but a Douglas bag did seem to absorb NO and the material
of the bag became sticky. The use of teflon or teflon coated tubing to connect the reservoir or
the subject to the analysers appeared to minimise NO loss.
In view of the purpose of the studies, the online technique seemed more appropriate as it
allowed comparison of signals throughout the exhalation and allowed an alteration of the test
conditions to investigate how this affected NO results. A slow controlled exhalation from total
lung capacity appeared to be the most satisfactory exhalation for observing the results. This
manoeuvre yielded obvious NO and CO2 traces and most people, including most children in
the age group studied, could be easily trained to perform this correctly. Thus I could discard
the reservoir system for most of the studies which I believe excluded another uncertain
element from test measures.
5.5 Other measurements
For all the experiments utilising the healthy adult volunteers and normal and asthmatic
children, a respiratory examination was carried out, and weight (minimal clothing, no shoes)
and height were recorded on a digital Seca scale (Seca 770 medical scales, Seca Ltd, 4802
Glenwood Rd, Brooklyn NYI1234, USA) and a Harpenden stadiometer (Harpenden Portable
Stadiometer, Crosswell, Crymych, Pembrokeshire, SA41 3UF, UK) respectively. Lung
function was measured according to the American Thoracic Society (ATS) criteria (American
Thoracic Society and Association. 1994) on a compact vitalograph (Vitalograph Ltd, Maids
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