Environmental influence on the measurement of exhaled nitric oxide concentration in school children: special reference to methodology.
BACKGROUND
Measuring exhaled nitric oxide (eNO) is a noninvasive and useful method for evaluating the correlation between airway inflammation and air pollution. The method is being used in studies; however, the effects of polluted air on eNO values are poorly understood. If polluted air significantly affects eNO concentrations, then it would be hard to evaluate the concentration of eNO, particularly in epidemiological measurements to detect the effects of airway inflammation, such as that in bronchial asthma. Thus, we hypothesized that short-term exposure to air pollution affects eNO values.


OBJECTIVE
To study the effects of environmental nitrogen oxides on the measurement of eNO concentration.


METHODS
A total of 19 school children who lived on a large street with heavy traffic with random allocation were studied. Subjects with bronchial asthma were identified with a questionnaire. Suspended particulate matter. including particulate matter with an aerodynamic diameter < or =2.5 microm (PM(2.5)), optical black carbon, nitric oxide (NO), nitric dioxide (NO(2)), and nitrogen oxides (NO(X)), were measured at a fixed place along the street every hour for 11 consecutive days. The concentrations of NO and NO(2) for each subject were measured by an individual 2-pyenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl sampler, and the concentration of eNO was measured with the off-line method.


RESULTS
Of 19 subjects, 3 were found to have bronchial asthma. The level of each pollutant for 11 days peaked during the mornings (6;9 a.m.) and evenings (6;9 p.m.) due to traffic jams; average eNO values in healthy subjects and those with asthma were 27.1 +/- 9.7 and 57.7 +/- 18.6 ppb (p=0.098), respectively. It was found that the eNO value remained high when the mean values of various pollutants remained high for 8 hours before the measurements. It was estimated that the mean eNO values increased by 1.08 ppb (95% CI: 0.72;1.45) when the mean NO(X) value for the previous 8 hours reached approximately 10 ppb.


CONCLUSIONS
We conclude that short-term exposure to polluted air of at least 8 hours before measurement affects eNO values. Therefore, caution should be exercised when measuring eNO value in epidemiological studies.
Murata
Akira
A
Department of Internal Medicine, Division of Pulmonary Medicine, Nippon Medical School. a-murata@nms.ac.jp
Kida
Kouzui
K
Hasunuma
Hideki
H
Kanegae
Hiroshi
H
Ishimaru
Yasushi
Y
Motegi
Takashi
T
Yamada
Kouichi
K
Yoshioka
Hiroko
H
Yamamoto
Kazuo
K
Kudoh
Shoji
S
D000393:Air Pollutants; D000397:Air Pollution; D001249:Asthma / Q000378:metabolism; D001944:Breath Tests / Q000379:methods; D002648:Child; D002675:Child, Preschool; D004781:Environmental Exposure; D004784:Environmental Monitoring / Q000379:methods*; D016021:Epidemiologic Studies; D005260:Female; D006801:Humans; D008297:Male; D009569:Nitric Oxide / Q000032:analysis*; D009589:Nitrogen Oxides; D011897:Random Allocation; D013997:Time Factors
D000393:Air Pollutants; D009589:Nitrogen Oxides; D009569:Nitric Oxide