View - ResearchSpace@Auckland - The University of Auckland

The second set of exhalations involved a reservoir system (see Figure 7.5):
r The ambient level is checked to make sure it is high - greater than the levels of known
exhaled NO results of the subjects, ambient NO > 75ppb.
o A reservoir bag (made of aluminium) is filled from a tank of NO free air (measured NO
level 0-2ppb).
o The reservoir bag is switched on-line to the analysers and the NO level in the bag is
checked to be < 5ppb.
o The subject breathes for 5 minutes from the reservoir bag. The subject exhales through a
one-way valve to avoid reservoir contamination.
o The analysers sampled from the reservoir system between exhalations.
o For the measured exhalation the connections were turned so that the subject exhaled to the
analysers.
o The subject exhales at a constant mouth pressure of 4mmHg voluntarily controlled by the
subject observing the pressure gauge and keeping it at level '10' on the scale.
o The subject exhales at a constant flow at 5O0mls/min voluntarily controlled by the subject
observing the rotameter, keeping it at '3' on the scale.
o At the end of each exhalation the connections were reversed to allow the subject and the
analysers to continue to sample from the low NO reservoir.
o This means none of the analysers are exposed to the high ambient level of NO during this
set of 5 exhalations.
The third set of exhalations was carried out in the standard manner:
r The measurements made were a repeat of the first set detailed above.
o Between exhalations the subject was breathing as normal in the known high ambient NO
level.
o Between exhalations the analysers were sampling as usual from the known high ambient
NO level.
Note: in this experiment the measurement used was NO plateaux rather than NO peak levels,
as the NO dropped from high level during the first and third set therefore a peak was not
obvious, while a plateau was more easily established.
7.5.4 Results
The ambient NO concentration was variable, although usually did not change quickly but
drifted up and down over hours. To demonstrate the appearance of the changing background
r64