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The exhalations were carried out in the standard manner:
o The subject abstains from food and drink for 4 hours prior to the experiment.
o The subject sits at rest for at least 5 minutes.
r The chart recorder is started 30 seconds prior to each exhalation to document baseline pre-
exhalation measurements.
o The subject puts on nasal clips 5 seconds prior to each exhalation and exhales by mouth,
and removes the clips between exhalations.
o The subject inhales to total lung capacity then performs a slow vital capacity manoeuvre
to residual volume over 30-60 seconds.
o The exhalations occur 3 minutes apart.
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 for 5 exhalations at each of 4 expiratory flows. The
flow is voluntarily controlled by the subject keeping the rotameter at specific levels:
Flow Rotameter level
250 mls/min 1.5
500 mls/min 3.0
750 mls/min 4.5
1100 mls/min 6.0
o The flow rate at which participants started, either 25Omls/min and increasing
consecutively or 1l00mls/min and decreasing consecutively, was made by tossing a coin.
o The subject continues until 5 exhalations at each flow level adequate for measurement are
made.
o A final set of measurements at the first flow was made.
o The subject was breathing ambient air when the natural background level of NO was less
than 10ppb.
7.3.4 Results
The mean peak concentrations of NO at the four expiratory flow settings were 79.0ppb (SEM
15.5) at 250mls/min, 67.8ppb (SEM 13.5) at 500mls/min, 59.lppb (SEM ll.2) at 75Omls/min
and 54.1ppb (SEM 10.7) at ll00mls/min (see Table 7.1). There were strong linear relations
between the NO concentrations obtained at the four flow levels for each individual subject
with a correlation coefficient of 0.85 (see Figure 7.1). The analysis of variance showed a
highly significant difference across the flow rates (p