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measurement with variable expiratory mouth pressure (Hogman, Stromberg et al. 1997;
Silkoff, McClean et al. t997), but another showed increasing exhaled NO concentrations with
increasing expiratory pressure from two to ten cmHzO (Kondo, Haniuda et al. 2003). Our own
findings suggested the opposite with a reduction of exhaled NO with increasing mouth
pressure in two of ten subjects (Byrnes, Dinarevic et al. 1997). However, as noted in the 2005
recommendations, a pressure above 20cmHzo should be avoided as it may be "uncomfortable
for patients or subjects to maintain". Indeed, I think this may have contributed to the fact that
there was a falling off of the exhaled NO in our study in two subjects. Having tried it
repeatedly myself, while pressures of 4mmHg (5.4cmHzO) and 8mmHg (10.9cmHzO) were
easy to maintain, l2mmHg (16.3cmHzO) became a little more difficult but l6mmHg
(21.8crnHzO), the highest expiratory pressure sampled in our study, was very tiring to exhale
against, and 2OmmHg Q7.2cn*l2O) almost impossible to maintain and therefore was not
used. One needs to recall that in the earlier studies a far longer exhalation time was also
required with the older modified analysers.
9.3.1 (iii) Nasal clips and breath-holding
While the early studies varied as to whether or not nose clips were used, the current
recommendation is not to wear them when doing exhaled NO in any of the methods of
measurement as this may actually increase the risk of having nasal and sinus contamination of
the oropharyngeal and exhaled sample (American Thoracic Society and European Respiratory
Society 2005). The previous standards suggested that a nose clip may be worn to prevent
inhaled air to contaminate the exhaled sample (see below) (Baraldi, de Jongste et al.2002).
In addition, the inhalation is now recommended as being through the mouth with higher initial
exhaled NO demonstrated following an inhaled breath through the nose when compared to
inhalation through the mouth @hillips, Giraud et al. 1996; Robbins, Floreani et al. 1996).Any
degree of breath-holding also results in NO accumulation in the nasal and oropharyngeal
spaces giving higher exhaled levels @ersson, Wiklund et al. 1993; Lundberg, Weitzberg et al.
L994; Kharitonov, Chung et al. 1996; Kimberly, Nejadnik et al. 1996; Massaro, Mehta et al.
1996; Sato, Sakamaki et al. 1996). Breath-holding was shown to increase NO levels in a time
dependent manner in atopic and healthy subjects (Martin, Bryden et al. 1996). Breath-holding
appears to affect the peak more than the plateaux levels in healthy and asthmatic subjects
(Shinkai, Suzuki et al.2O02). The effect of breath-holding also depended on the ambient NO;
when the ambient NO was greater than 10ppb, exhaled NO was decreased whereas if the
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