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The ATS guideline states "terms such as NO release, NO excretion, NO secretion and NO
production are to be discouraged when referring to Voo" (American Thoracic Society
European Respiratory Society 2005).
A constant expiratory flow is required with any exhalation measured and has been
reconrmended following the findings from early studies. This is most easily achieved with
appropriate biofeedback using a gauge or computer display for subjects to maintain expiratory
flow within specified limits. All newer machines as exemplified by the companies that took
part in the 2005 recommendations (Aerocrine, Eco Physics, Eco Medics, Ionics Instruments
and Ekips Technologies) have these available. However there are other options which include
the use of dynamic resisters (Kharitonov, Gonio et al. 2003), operator controlled flow
(Baraldi, Scollo et al. 2000), starling resisters (Hogman, Stromberg et ^l' 1997; Tsoukias'
Tannous et al. 1998) and server controlled devices (Silkoff, Bates et al. 2004)' These
techniques have usually been tried in young children but can also be useful in other subjects
that have difficulties controlling their exhalation such as those with neuromuscular disease' In
children aged 4-g years, 507o could not perform the single breath online technique adequately'
However, the addition of a dynamic flow resister allowed exhalation with a variable mouth
pressure while maintaining constant expiratory flow and resulted in only 77o of the children
unable to perform the manoeuvre (Baraldi, scollo et al. 2000).
9.3.1 (ii) Mouth Pressure
An expiratory mouth pressure of between five and 2}cttttLzO is currently recommended' This
degree of resistance is needed for velum closure of the soft palate to prevent nasal
contamination of the exhaled NO and has been validated by nasal COz measurements (Silkoff'
McClean et al. L997) and nasal argon insufflation (Kharitonov and Barnes 1997)' Many
studies have confirmed higher sinus and nasal levels when comparing sinus' nasal' exhaled
and/or lower airway sampling (Alving, weitzberg et al. 1993; Lundberg, Rinder et al' 1994;
Lundberg, weitzberg et al. 1994; Schedin, Frostell et al. 1995; Dillon, Hampl et al' 1996;
Imada, Iwamoto et al. 1996; Kimberly, Nejadnik et al. 1996). The other options described to
prevent nasal contamination has been continuous nasal aspiration (Silkoff, Kesten et al' 1995)
or to inflate a balloon in the posterior nasal pharynx to separate the two compartments
(Schedin, Frostell et al. 1995; Kimberly, Nejadnik et al. 1996). Clearly, exhaling against an
appropriate mouth pressure is the easiest option and has been most widely used'
Unlike the effects of flow on NO, the effects of varying mouth pressure has not demonstrated
consistent findings in all studies. Two studies showed no difference in plateau NO
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and