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Model 2107, Dasibi Environmental corporation, Glendale, california, united states
of America.
Model 42, Thermoelectron, Warrington, United Kingdom'
Sievers Model 280A, GE Analytical Instruments, Boulder, Colorado' United States of
America.
These had differing response times ranging from 5-25 seconds while the subsequent
purpose built models from 2000 improved this to 0.02-0.3 seconds. The above models all
had differing sampling flows which ranged from 50-500mls/s (machine sampling rate)'
and different sensitivities to NO ranging from 0'3 to 5ppb'
2. Different methods of sampling - the three commonest techniques used for sampling the
exhalation were:
o Direct to the machine.
o Using a t-piece or side arm sampling'
o From a reseryoir of stored exhalations'
3. Variation of reservoir and tubing materials -
the type of material used to collect the
sample also varied which may have resulted in some absorption or adsorption of No as
discussed in Chapter 4. This is particularly important in reservoir studies with the use of
bags and tubing made of polyethylene, tedlar, mylar, teflon coated, metal and 'Douglas'
bags (a type of anaesthetic bag made of rubber)'
4. Method of cleaning and/or filter use - there was also the possibility of interference from
hygiene and infection control procedures. This isn't discussed in the early papers' At the
time, as currently, standard infection control procedures were recommended with regard
to doing routine spirometry (American Thoracic Society and Association' 1994)' It is
likely most researchers were following a similar type of infection control when measuring
No and this may have resulted in interference - either with use of inline filters and/or
chemicals for cleaning. Data presented in one abstract showed that the NO concentration
was greatly augmented by alcohol containing disinfectant (Meijer, Kerstjens et al' 1996)
at a time when the use of chlorhexidine (also an alcohol containing disinfectant) was
common in usual lung function laboratory hygiene practices' One study showed no
differences between a disposable mouth piece (sievers@) and a mouth piece containing a
filter (FIEpA) (Irme, Kasahara et a.^.2002), but there has been little research in this area'
5. Different exhalation techniques - subjects were asked to perform exhalation differently:
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