Project at a Glance

Title: Effects of air pollution on airway function

Principal Investigator / Author(s): Nadel, J. A.

Contractor: UC San Francisco

Contract Number: A9-115-30

Research Program Area: Health & Exposure

Topic Areas: Health Effects of Air Pollution, Impacts


In a series of studies, we have shown that adult subjects with mild asthma develop greater bronchoconstrictlon on inhaling sulfur dioxide than non asthmatic subjects. When exposed to sulfur dioxide at rest, the asthmatic subjects developed significant bronchouonstriction sometimes associated with wheezing and shortness of breath -- on inhaling 1 and 3 ppm of sulfur dioxide In air, whereas non asthmatic subjects developed bronchospasm only on inhaling 5 ppm. In additional studies, we have shown that the increase in the rate and depth of breathing required for exercise potentiates the response of asthmatic subjects to sulfur dioxide: when exposed to sulfur dioxide for 10 meanwhile performing light to moderate exercise, our subjects developed bronchospasm on inhaling 0.50 and 0.25ppm. Additional studies showed that the nose offers partial protection against the effects of sulfur dioxide on the airways. When our subjects performed light exercise while breathing sulfur dioxide through a facemask (permitting breathing through the nose and mouth), the bronchoconstrictlon caused by sulfur dioxide was less than that obtained when our subjects Inhaled sulfur dioxide through a mouthpiece. At higher levels of exercise, the protection afforded by oronasal breathing decreased, probably because of the greater proportion of air bypassing the nose as ventilation increased. Taken as a group, our studies show that people with asthma constitute a subgroup of the population who develop bronchoconstrictlon often with symptoms of wheezing and shortness of breath -- on brief exposure to levels of sulfur dioxide sometimes found in urban air. We have also found that the responsiveness of asthmatic subjects to sulfur dioxide can be diminished both by treatment with dlsodium cromoglycate -- a drug commonly used In patients with asthma and by repeated exposures to sulfur dioxide at 30-minute intervals. This tolerance to sulfur dioxide disappears within 24 hours. In studies of experimental animals, we have shown that Inhalation of sulfur dioxide causes rapid shallow breathing and coughing and that these changes in the pattern of breathing occur even If bronchoconstriction Is blocked by pretreatment with an anti-asthmatlc medications. Similar ventilatory responses were elicited by delivery of much smaller doses to the upper airways than to the lower airways. This suggests that the effects of sulfur dioxide Inhaled through the mouth are likely to be reflex in nature and due to stimulation of nerve endings In the upper airway, possibly In the larynx. This work was submitted in fulfillment of contract number A+115-30 under the sponsorship of the California Air Resources Board.

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