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(Hyde, Geigel et al. 1997; Tsoukias and George 1998; Tsoukias, Tannous et al. 1998; Silkoff,
Sylvester et al. 2000).
One of the reasons that higher levels were thought to be obtained using either single or tidal
breathing into a reservoir was because of an open soft palate and upper nasopharyngeal
contamination (Sharma, Traylor et al. 1987; Schilling, Holzer et al. 1994; Kimberly, Nejadnik
et al. 1996; Kharitonov and Barnes 1997). A single exhalation against even low resistance
into the reservoir gave much lower levels (Massaro, Gaston et al. 1995). A resistor is now
included in most reservoir bags with a recorlmendation of standard expiratory flow and
standard expiratory pressure of 5cmHzO for both single breath (Massaro, Gaston et al. 1995;
Deykin, Halpern et al. 1998) and tidal breathing reservoir collections (Canady, Platts-Mills et
al. 1999; Jobsis, Schellekens et al. 2001). A dynamic flow restrictor is possible to aid the
operator to standardise the exhaled breath with less able subjects by altering the resistance to
give a standard flow during the exhalation @ijnenburg, Lissenberg et al. 2002), although
again I imagine this must introduce an element of complexity.
From 1999, inhaling via the mouth prior to exhalation into the reservoir bag was added to the
protocol. By 2005 this recommendation had been revised to include the inhalation of NO free
gas or via an NO scrubbing filter in the inspiratory limb. High concentrations of NO in the
inspired air of greater than 20ppb significantly increased the offline exhaled NO
measurements (Gustafsson, Irone et al. l99l; Zayasu, Sekizawa et al. 1997). Again wearing
a nose clip and breath holding are not recommended for similar reasons to the single breath
online measurements (see section 9.3.1 (ii)) (Jobsis, Schellekens et al. 2OOt). Following these
guidelines, subjects tested on multiple days had a variation between 1 and 5ppb, which is
similar to that found in immediate online measurements, although in this study the collection
was delayed for more than three seconds to discard the dead space (Borland, Cox et al. 1993;
Massaro, Mehta et al. 1996). For the standard method to measure off-line collections as either
single exhaled breaths or as tidal breathing collections see Table 9.2.
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