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in different colours that became the standard: NO in green, COz in red, and mouth pressure in blue. As
this is an example from the direct method of analysis, flow is not denoted. The measurements of each
parameter were calculated from the calibration markings (see Chapter 6).
As can be seen in Figure 5.2, the NO rose to a plateau which often had additional small
deviations, the COz continued to rise to a peak throughout the exhalation, the mouth pressure
(and flow with the t-piece measurements) were under voluntary control and therefore less
exact plateaux markings were seen and the lines of measurement were drawn through the
middle to determine that they had been appropriately close to requested levels. Note the offset
of the traces from the different analysers which were displayed in different colours that
became the standard: NO in green, COz in red, and mouth pressure in blue. As this is an
example form the direct method of analysis, flow is not denoted but when measured, as
during the t-piece sampling technique, was displayed as a brown trace. The measurements of
each parameter were calculated from the calibration markings.
We (Carolyn Busst and myself) checked the reported sampling rates of the NO and COz
analysers. As mentioned, the sampling rate was determined by the vacuum pump within the
NO analyser and had a fixed rate. Similarly, the sampling rate of the CO2 analyser was also
determined by the vacuum pump which could apparently be adjusted by pressing the
calibration button on the front of the analyser panel and the rate changed by pressing the up
and down arrow keys. We left the sampling rate at the setting it was on when we received it
from rhe Adult Physiology Laboratory (Royal Brompton Hospital). This was in the middle of
the range suggested by the manufacturers and was used for all assessments. The check of the
machines' sampling was repeated a number of times prior to development of the protocol for
the experiments and again between the methodological experiments conducted with adult
subjects and commencement of the studies on paediatric subjects. We listed what was to
become our standard procedure as the following steps:
o Connect the outlet line from the mouthpiece t-piece connection to the lower port of the
rotarmeter.
o Turn the rotameter needle valve off to ensure that the room air cannot be sampled via
the rotameter.
o Disconnect the pneumotachograph from the rotameter.
o Run the paper to record zero sampling.
o Connect the outlet side of the pneumotachograph to the inlet of the mouth piece.
tt4