INFLUENCE OF AMBIENT NITRIC OXIDE (NO) ON THE EXHALED NO TEST

Nitric oxide (NO) is produced by various cells within the respiratory tract. In healthy individuals, exhaled NO is mainly produced in the nasal airway. The most widely used technique for measuring NO in exhaled air is the chemiluminescence method. In the present study, exhaled NO was collected in a sampling bag placed over the mouth and nose, while nasal NO was sampled directly from the nasal cavity. Both exhaled and nasal NO levels were measured using a ML9841 chemiluminescence NO analyzer, which has a detection limit of 1 part per billion (ppb).The purpose of this study was to determine whether ambient NO concentrations influence the levels of exhaled NO.Subjects and Methods.Twenty-six healthy volunteers were enrolled in the study. One volunteer was examined four times, cosequently twenty-nine samples of exhaled NO were obtained. Exhaled NO and nasal NO were measured after the subjects had inhaled either NO-free air or ambient room air.Ambient NO was tested before each measurement of exhaled NO. Exhaled NO was then collected for 20 seconds in a sampling bag placed over the mouth and nose of the volunteer. The inspiration and expiration times were both 4 seconds. The recommended exhalation flow rate for oral and nasal breathing is 9L/min. Oral exhalation was measured using a resistance technique, which is the simplest and most effective method for preventing the contamination of exhaled air with nasal NO. Nasal cavity air was sampled every 20 seconds at a rate of 3.6L/min while the subjects held their breath.Results.Ambient NO concentrations ranged from 1.3 to 122ppb. Exhaled NO and nasal NO levels were higher when subjects inhaled ambient room air than when they inhaled NO-free air. In addition, significant correlations were observed between exhaled NO, nasal NO and ambient NO levels. Exhaled oral NO concentrations were significantly correlated with the ambient NO concentration (r=0.5982, p<0.001). Exhaled nasal NO concentrations (r=0.4928, p<0.01) and nasal NO concentrations (r=0.406, p<0.05) were also correlated with the ambient NO concentration.ConclusionsExhaled NO and nasal NO concentrations are influenced by the concentration of inhaled ambient NO. The dead space, which is the unventilated volume of the airway, was influenced by the ambient NO concentration. The dead space volume was about 15-19% of the ventilated volume. In our study, orally inhaled NO, which reflects the degree of contamination by ambient NO, was approximately 21.3%. The results of the present study suggest that inhaling ambient air containing a high concentration of NO effects the levels of exhaled NO. In usingexhaled NO tests to assess patients with airway inflamations, such as asthma, NO-free air should be inhaled in order to prevent contamination by ambient NO.