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pneumatisation. A progressive decrease in NO concentration had been found when sampling
progressively down the respiratory tract from nasal passages (Alving, Weitzberg et al' 1993;
Kimberly, Nejadnik et al. 1996), oral cavity (Gerlach, Rossaint et al. 1994), and below the
vocal cords (Lundberg, Weitzberg et al. 1994). The slow expiration time, particularly in the
direct measurements, did raise the possibility that I was merely recording inspired air,
contaminated by NO produced from the nose and sinuses, and exhaled unchanged' Schedin et
al showed the difference in exhaled NO in tidal breathing when the inhalation was by nose
giving a mean of 64ppb and by mouth giving a mean of 13ppb (Schedin, Frostell et al' 1995)'
Similarly when single exhalations were measured, nasal inhalation gave exhaled oral results
of 32ppb and22ppbwhile inhalation by mouth gave exhaled oral results of gppb and 9ppb in
two other studies (Alving l993;Kimberly 1996). However using a faster (t-piece) method in
our own study did not reveal an abrupt discontinuity suggestive of emptying unchanged dead
space prior to measuring true exhaled NO. The other area of difference between groups that
was studied by others at this time, which I did not exatnine, was the effect breath-holding had
on the subsequent exhaled NO. Using collection into a reservoir system, Sato et al showed
that the NO levels increased in proportion to the duration of exhalation and to duration of a
pre-exhalation breath-hold in 16 controls (Sato, Sakamaki et al. 1996)' In 18 controls Martin
et al reported the increase of exhaled No from no breath-hold at ll.lppb to l5'6ppb and
32.lppb in exhalations following ten and 60 second breath-holds respectively (Martin, Bryden
et al. 1996). The findings were simil ar in 32 subjects with allergic rhinitis from a baseline
exhaled NO at 16.2ppb to 34ppb following a ten second breath-hold and 62ppb following a
sixty second breath-hold (Martin, Bryden et al. 1996). Kimberly et al in eight controls showed
an increase in exhaled No from Tppb to 23ppb with a 30 second breath-hold (Kimberly'
Nejadnik et al. 1996). persson et al recorded the most dramatic increase from 3.25ppb with
tidal breathing to 100.25ppb with a breath-hold of 60 seconds (Persson, Wiklund et al' 1993)'
Kharitinov et al determined that a breath-hold for 20 seconds gave an initial peak of NO but
end expiration values were similar to non breath-hold results (Kharitonov, Chung et al' 1996)'
However, I believed that the finding with the ambient NO in this chapter suggested that
measurements of exhaled NO must be done on days with low ambient backgound NO' or by
using an NO-free circuit such as described.
The final experiment may seem an unusual test to have performed, but was based on a chance
finding that following drinking a glass of water, the NO levels on the next exhalations
dropped dramatically. The reason I thought that this may be significant was that when doing
lung function or full inspiratory/expiratory manoeuvres, a corrmon side effect, particularly in
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