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ambient No was less than 10ppb the exhaled No was increased after a 10 second breath-hold
(Jobsis, Schellekens et al. 2001).
9.3.1 (iv) The recorded measurement
The NO recorded in the literature has been peak, plateau, area under the curve or NO plateau
signal at COz peak. The current recommendation is for plateau levels to be reported' unless
calculating NO output. This requires a plateau of three seconds following exhalation of at
least six seconds for participants older than 12 years of age' or two seconds following
exhalation for at least four seconds for children less than 12 years of age' The peak
measurement has shown more variability as influenced by the degfee of dead space' ambient
NO and inspiration taken via nose or mouth. An expiratory flow of 50mls/s ensures an
acceptable time to plateau, an acceptable rate of decline in lung volumes and is appropriate
for children at less than 12 years of age, as well as those with vital capacities less than one
litre (Pfaff and Morgan l994;Canady, Platts-Mills et al. 1999; Franklin, Taplin et al' 1999;
Kissoon, Duckworth et al. 1999).
9.3.1 (v) The effect of ambient nitric oxide
Recommendations since 199? have been to record the ambient NO as this fluctuates
considerably. A note from one of the authors (A Sovijarvi, Helsinki University Central
Hospital, Finland) in this document states; the ambient NO was noted to vary between I and
600ppb during winter months in their studies (Kharitonov, Alving et al. 1997). Initially it was
suggested that measurements should only be performed with an ambient NO less than 40ppb'
with improved standardisation and more sensitive and rapidly responding analysers this is
now too high. The 2005 recommendation is that the ambient NO be less than 5ppb and/or that
subjects inhale NO free air while being tested. The newer NO analysers including the smaller'
more transportable units such as the MINO@ (Aerocrine AB, Solna, Sweden) or z-700 No
meter @asibi Environmental Corporation, Glendale, California, United States of America)
have a scrubbing facility within the inhalation limb. This may be more important for reservoir
collections during tidal breathing where an increased amount of ambient NO is exhaled and
thus collected. In our experiments we elected to measure only when the NO in ambient air
was less than 10ppb. However on many days this precluded measurement which delayed the
experiments. Unlike other researchers, we found exhalation from a high NO concentration
compared to exhalation from a low NO concentration resulted in a drop in the overall NO
level as discussed in Chapter 7. On review now, it may have been because we were waiting
for a plateau to develop with a drop from the high ambient NO reading and it took some time
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