The Health Impact of Nitric Oxide: Effects on Lung Function and Cellular and Biochemical Processes in Healthy Humans

DISCLAIMER The statements and conclusions in this report are those of the contractor and not necessarily those of the California Air Resources Board. The mention of commercial products, their source, or their use in connection with material reported herein is not to be construed as either an actual or implied endorsement of such products. ABSTRACT Epidemiological studies have reported associations between ambient concentrations of nitrogen dioxide (NO 2) and morbidity, but human exposure studies with ambient concentrations of NO 2 have not shown significant effects. Since a significant concentration of nitric oxide (NO) is often present in ambient air, the epidemiological findings attributed to NO 2 could be due to NO. This literature survey addressed whether an ambient air quality standard for NO was warranted, and/or whether there was evidence that inhalation of ambient NO has health effects that should be investigated further. While it is clear that NO is biologically active throughout the body, and that ambient NO could induce health effects, the review concludes that currently there is insufficient evidence to warrant an ambient air quality standard for NO. The review concludes that NO can be both beneficial and injurious, and suggests that ambient concentrations of NO could affect cardiopulmonary regulation, pulmonary inflammation, asthma and other inflammatory lung diseases, host defense, immune responses and platelet function. Suggested areas for further research include: (1) biochemical and/or cellular changes in the lungs indicative of pulmonary inflammation; (2) effects on asthma and other inflammatory diseases; (3) whether environmental NO is beneficial; (4) effects on platelet function; (5) effects on endogenous NO production; (6) effect on ventilation/perfusion (V A /Q) mismatching; and (7) the role of NO in epidemiological findings attributed to NO 2 , carbon monoxide (CO) and particulate matter (PM). 6 EXECUTIVE SUMMARY Background: The objective of this paper was to critically review literature on nitric oxide (NO) to determine whether there are sufficient data to suggest that exposure to ambient concentrations of NO causes adverse health effects. Epidemiological studies have reported associations between ambient concentrations of nitrogen dioxide (NO 2) and morbidity, including incidence of respiratory infections, croup, exacerbation of asthma, bronchitis, ischemic cardiac and cerebrovascular diseases at NO 2 concentrations commonly measured in ambient air. However, human exposure studies conducted with ambient concentrations of NO 2 alone have not shown significant effects, even at concentrations higher than typically observed in ambient air. This, along with the finding that …