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to settle. We may have been measuring the latter part of the exhalation in error and this
potentially may give lower levels than the peak or the true plateau. Thus, we may have been
comparing the plateau in the exhalation from the low ambient NO with the last part of the
exhalation from the high ambient NO. In two studies NO was significantly higher when
measured in a total of 215 children including healthy controls, non-asthmatic atopics and
asthmatics at times of high ambient NO (>10ppb, mean l9ppb) and at times of low ambient
NO (10ppb was the cut-off used) and
measured NO increased if the ambient NO was lower (NOclOppb) (Jobsis, Schellekens et al.
2001). Nasal NO in healthy children correlated with ambient NO and, in those children
greater than 12 years, it was the only factor correlating with the measured expiratory levels
(Struben, Wieringa et al. 2005). More recently there has been a study suggesting that even
levels of 5-10ppb ambient NO may have an effect on the exhaled results, with no difference
seen at less than 5ppb, upholding the most recent recommendations (Franklin, Turner et al.
2004).
Other studies have examined effects of pollution on exhaled NO. Ambient NO levels, as well
as ambient CO levels, were positively correlated with the exhaled NO results in 16 non-
smoking healthy subjects (Van Amsterdam, Verlaan et al. 1999). Mean air pollution was also
correlated with the exhaled NO levels in 16 healthy subjects measured on two separate days
(van Amsterdam, Verlaan et al. 1999) and 18 subjects measured on four separate days
(Steerenberg, Snelder et al. t999) at times of differing pollutant levels. At times of high
ambient NO, an increased risk of developing respiratory symptoms described as "sore throat,
runny nose, having a cold or being sick at home in the following week" was also shown in 68
children (Fischer, Steerenberg et al.2N2).
9.4
Online spontaneous or tidal breathing measurement
A single exhaled breath with online measurement remains the measurement of choice.
However, in some studies 50Vo of children aged 4-8 years of age @araldi, Scollo et al. 2000),
l\Vo of children aged 9-16 years (Baraldi, Scollo et al. 2000) and 30Vo of children aged 4-16
years of age (Jobsis, Schellekens et al. L999) could not pedonn this technique appropriately.
Online measurement during tidal breathing, usually as a mean of three breaths, has been
explored as an option for younger children and infants. One study measured exhalation
following quiet breathing with the operator controlling the expiratory flow by varying
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