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Drazen et al. 1994; Nelson, Sears et al. 1997; Canady, Platts-Mills et al' 1999; Jobsis'
Schellekens et al. 2001).
Thirdly, there was debate as to whether the whole exhaled breath should be collected. Early
experiments discarded the first part of exhalation to reduce contamination by inhaled ambient
NO, dead space and nasopharyngeal space with a good correlation demonstrated between the
remaining exhalate and single online exhalation (Borland, Cox et al.1993; Massaro, Mehta et
al. 1996). Similarly, studies that discarded the first tidal volume when measuring during tidal
breathing also achieved a closer approximation to online values (Paredi, Loukides et al' 1998;
Jobsis, Raatgeep et al. 2001). The uncertainty was in deciding the absolute amount to discard
and how to get consistency across subjects. While 150 to 200mls were used in the adult
studies even greater uncertainty existed in the correct amount to discard in paediatric studies'
The 'discard' was achieved employing spring loaded or manually activated valves' or low
compliance reservoirs placed in series with the main collection vessel. Subsequently
collecting the whole exhalation was shown to provide identical sensitivity and specificity as
single breath online recordings, despite the fact that the absolute NO levels were not identical
(Silkoffl Stevens et al. 1999; Djupesland, Qian et al. 2001; Jobsis, Raatgeep et al' 2001;
Deykin, Massaro et a:.2002). The standardisation has therefore altered accordingly between
lggT and2005 from discarding the first o.7sLexhaled (or 0.5L if the vital capacity was less
than 2L) @uropean Respiratory Society 1993; Kharitonov, Alving et al. 1997) to collecting
the entire breath (American Thoracic Society and Association. L999;Baraldi, de Jongste et al'
2002).
Similar across all methods, higher flow rates result in decreased concentration of NO
recovered from the exhaled reservoir sample (Hogman, Stromberg et al' t997; Silkofl
McClean et al. 1997). Despite this, subject group differences can be seen at expiratory rates
between 50 and 500mls/s as long as the flow remains identical for all subjects in any
comparison (Jobsis, Raatgeep et al. 2001; Deykin, Massaro et al' 2002)' With collection of
tidal breathing, using standard expiratory flow reduces variability and improves comparison
with online results (Kissoon, Duckworth et al. 2000). This can be controlled by the subject or
by the operator (Massaro, Mehta et al. 1996; Baraldi, Azzolin et al. 1997i Baraldi, Carra et al'
t999; Baraldi, Dario et al. 1999; Jobsis, Schellekens et al. 2001). The tasldorce ultimately
proposed recommendations for 50mls/s exhalation for both offline and online collections as
showing good correlation in the paediatric arena (Baraldi, de Jongste et al.2002)' It is still
possible to sample different compartments using a different flow even with this technique
2r7