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women who coincidently experienced worsening of sputum scores, eosinophils and lung
function pre-menstrually (Oguzulgen, Turktas et al.2002). No difference has been shown in
exhaled NO during pregnancy between 10 and 42 weeks (Morris, Caroll et al. 1995).
9.7.5 Food and beverages
In our own study, we found that drinking water prior to exhalation transiently reduced NO
levels @yrnes, Dinarevic et al. 1997). Caffeine also decreased exhaled NO in one paper
(Bruce, Yates et at.2002) but not in another (Taylor, Smith et al.2004). Alcohol ingestion
reduced exhaled NO in both asthmatic and healthy subjects (Persson, Cederqvist et al. 1994;
Yates, Kharitonov et al. 1996) with a small decrease in exhaled NO observed up to 34 hours
after drinking (Jones, Fransson et al. 2005). Smoking also significantly reduces exhaled NO
and will this be discussed below with the studies on COPD subjects (see Section 9.15). The
reduced NO levels subsequent to both cigarette smoking and alcohol consumption was
suggested to be secondary to down regulation of iNOS (Steerenberg and van Amsterdam
20M).In contrast increased exhaled NO has been found after the ingestion of nitrite or nitrate
containing foods (such as lettuce) with a maximum effect occurring two hours after ingestion
(Zetterquist, Pedroletti et al. 1999; Olin, Aldenbratt et al. 2001). The gastric lumen has been
noted to have high levels of NO, therefore contamination with gastric air results in very high
exhaled NO (Lundberg, Weitzberg et al.1994).
9.7.6 Summary of physiologicalfactors that could alter nitric oxide levels
In conclusion, exhaled NO is likely to be higher in males than females, and relates to age
through childhood but not adulthood, possibly in relation to pneumatisation of the sinuses. It
is reduced with current smoking, recent ingestion of water, alcohol or caffeine and increased
with accidental gut contamination or after nitrogen-compound rich meals. There may be
differences throughout the 24 hour day in asthmatic subjects with nocturnal asthma, and
through the menstrual cycle in those who experience premenstrual exacerbations of asthma.
However, relationships with height, weight, surface area, menstrual cycle in non-asthmatic
women, or a circadian rhythm in non-asthmatic individuals has not been demonstrated.
Despite some of the findings above, there is only one range of 'normal' values given for the
results of measurement for oral or nasal results.
9.8 Nitric oxide levels in asthma and atopy
Since commencement of the studies on exhaled NO, more research has been conducted in
asthmatic populations than any other group; in particular assessing the use of NO for
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