EFFECT OF NITROGEN-DIOXIDE AND OTHER COMBUSTION PRODUCTS ON ASTHMATICSUBJECTS IN A HOME-LIKE ENVIRONMENT

Nitrogen dioxide (NO2) is one of a number of nitrogen compounds that a re by-products of combustion and occur in domestic environments follow ing the use of gas or other fuels for heating and cooking. In this stu dy, we examined the effect of two levels of NO2 on symptoms, lung func tion and airway hyperresponsiveness (AHR) in asthmatic adults and chil dren. In addition, in the same subjects, we examined the effects of th e same levels of NO2 mixed with combustion by-products from a gas spac e heater. The subjects were nine adults, aged 19-65 yrs, and 11 childr en, aged 7-15 yrs, with diagnosed asthma which was severe enough to re quire daily medication. All subjects had demonstrable AHR to histamine . Exposures were for 1 h on five separate occasions, 1 week apart, to: 1) ambient air, drawn from outside the building; 2) 0.3 parts per mil lion (ppm) NO2 in ambient air; 3) 0.6 ppm NO2 in ambient air; 4) ambie nt air + combustion by-products + NO2 to give a total of 0.3 ppm; and 5) ambient air + combustion by-products + NO2 to give a total of 0.6 p pm, Effects were measured as changes in lung function and symptoms dur ing and 1 h after exposure, in AHR 1 h and 1 week after exposure, and in lung function and symptoms during the week following exposure. Expo sure to NO2 either in ambient air or mixed with combustion by-products from a gas heater, had no significant effect on symptoms or lung func tion in adults or in children. There was a small, but statistically si gnificant, increase in AHR after exposure to 0.6 ppm NO2 in ambient ai r. However, there was no effect of 0.6 ppm NO2 on AHR when the combust ion by-products were included in the test atmosphere nor of 0.3 ppm NO 2 under either exposure condition. We conclude that a 1 h exposure to 0.3 or 0.6 ppm NO2 has no clinically important effect on the airways o f asthmatic adults or children, but that 0.6 ppm may cause a slight in crease in airway hyperresponsiveness.