THRESHOLD CONCENTRATION OF OZONE CAUSING AN INCREASE IN BRONCHIAL REACTIVITY IN HUMANS AND ADAPTATION WITH REPEATED EXPOSURES

Authors:
  • MDMJ DIMEO
    MJ DIMEO
  • MGMG GLENN
    MG GLENN
  • MHMJ HOLTZMAN
    MJ HOLTZMAN
  • JSJ R SHELLER
    J R SHELLER
  • JNJA NADEL
    JA NADEL
  • HBHA BOUSHEY
    HA BOUSHEY
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Abstract
To determine the lowest concentration of ozone that causes an increase in bronchial reactivity to histamine and to determine whether adaptation to this effect of ozone develops with repeated exposures, 19 healthy adult subjects were studied. Bronchial reactivity was assessed by measuring the rise in specific airway resistance (.DELTA.SRaw) produced by inhalation of 10 breaths of histamine aerosol (1.6% solution). In 5 subjects, bronchial reactivity was determined at 0900 and 1130 h on 4 consecutive days without exposure to ozone (group I). In 7 other subjects (group II), bronchial reactivity was assessed at 0900 and 1130 h on 3 consecutive days and subjects were exposed to 0.2 ppm of ozone from 0930-1130 h on the 3rd day. Seven additional subjects (group III) had bronchial reactivity assessed in a similar fashion for 2 days and then again on 3 consecutive days at 2-7 exposures to 0.4 ppm of ozone. Pre-exposure bronchial reactivity of the groups was the same and no change in bronchial reactivity occurred in the group tested repeatedly but not exposed to ozone. An increase in .DELTA.SRaw provoked by histamine was noted after the 1st exposure to 0.4 ppm but not to 0.2 ppm of ozone (P < 0.025). With 3 repeated 2-h exposures to 0.4 ppm on consecutive days the .DELTA.SRaw produced by histamine progressively decreased, returning to pre-exposure values after the 3rd exposure. The threshold concentration of ozone causing an increase in bronchial reactivity in healthy human subjects is between 0.2-0.4 ppm and adaptation to this effect of ozone develops with repeated exposures. The threshold concentration of ozone identified in other studies as causing changes in symptoms, lung volume or airway resistance also was between 0.2-0.4 ppm and the time course of the development of tolerance to ozone in these other studies was similar to that observed in this study. The appearance of symptoms, changes in pulmonary function and the increase in bronchial reactivity may be caused by a change in the activity of afferent nerve endings in the airway epithelium.