-Original-

Environmental Influence on the Measurement of Exhaled Nitric Oxide Concentration in School Children: Special Reference to Methodology

Akira Murata¹, Kouzui Kida¹, Hideki Hasunuma², Hiroshi Kanegae², Yasushi Ishimaru², Takashi Motegi¹, Kouichi Yamada¹, Hiroko Yoshioka¹, Kazuo Yamamoto¹ and Shoji Kudoh¹

¹Department of Internal Medicine, Divisions of Pulmonary Medicine, Infectious Diseases, and Oncology, Nippon Medical School
²The Center for Environmental Information Science

Introduction: 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.
Purpose: To study the effects of environmental nitrogen oxides on the measurement of eNO concentration.
Subjects and 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 ≤2.5 μm (PM_2.5), optical black carbon, nitric oxide (NO), nitric dioxide (NO₂), 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 NO₂ 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.
Conclusion: 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.

J Nippon Med Sch 2007; 74: 30-36

Keywords
Exhaled nitric oxide, nitrogen oxides, epidemiological study, short-term exposure, bronchial asthma

Correspondence to
Akira Murata, MD, Department of Pulmonary Medicine, Infection and Oncology, Nippon Medical School, 8F JPR Ichigaya-Building, 4-7-15 Kudan-minami, Chiyoda-ku, Tokyo 102-0074, Japan
a-murata@nms.ac.jp

Received, October 4, 2006
Accepted, December 4, 2006