Measurement of exhaled nitric oxide

Assessment of the value of exhaled NO (eNO) is an attractive tool for studying pulmonary disease, considering its wide advantages (i.e., fast analysis, noninvasive sampling, ability to measure large numbers of subjects [including children], and inexpensive in use). Increased concentrations of eNO have been observed in asthmatic patients' airway infections, allergic rhinitis, and bronchiectasis. During inflammation, specific and nonspecific stimuli elicit expression and de novo synthesis of inducible nitric oxide (iNOS). Once generated in the bronchiolar cells, NO is released from the tissue and diffuses to the lumen of the bronchiolis. Of the two sampling ways (on-line and off-line), the off-line method is suitable for monitoring environmental health effects of air pollution and for obtaining an impression of the prevalence of atopy in epidemiological surveys. For this off-line measurement, a balloon method is developed (sampling exhaled air at location) that includes a sample device assuring inflation of balloons at a controlled flow rate and back-pressure. Cigarette smoking and alcohol consumption significantly reduces NO levels in exhaled air because of downregulation of iNOS. Although eNO can be reliably measured and analyzed, the prospective value to detect asthma or allergy is rather low (low sensitivity and low specificity), which makes the diagnostic value of eNO for predicting either allergy or asthma doubtful. Promising results have, however, been observed in corticoid-sparing therapies under guidance of eNO. In addition, measurement of eNO helps to understand the mechanisms of pulmonary disease and may be useful in detecting adverse effects of air pollution.