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Principal Investigator: Dean Sheppard, M. D.
1 July 1986
ARB Contract No. A4-113-32 (Full Report)
ABSTRACT
By exposing subjects with asthma to aerosols of buffered and unbuffered solutions of sulfuric and hydrochloric
acid with a variety of concentrations of free hydrogen ion (pH) and total available hydrogen ion (titratable
acidity - the sum of free hydrogen ion and hydrogen ion bound to buffers), we were able to study the relative importance
of pH, titratable acidity and specific chemical composition in describing the bronchoconstrictor potency of acid
aerosols. Aerosols of unbuffered acids caused little bronchoconstriction down to pH 2, whereas aerosols of buffered
HCL and H2SO4 (buffered with glycine) caused titratable acidity-dependent bronchoconstriction in 7 of 8 subjects,
suggesting that titratable acidity might be a more important determinant of bronchoconstrictor potency than is
pH. We also studied the mechanism(s) by which sulfite aerosols cause bronchoconstriction. By comparing the bronchoconstrictor
potency of sulfite aerosols inhaled at 3 different pHs (pH 4, pH 6.6, and pH 9) we examined the relative importance
of the two different ionic forms of sulfite (HSO3- and SO3- ) and of the sulfur dioxide gas with which these ions
are in equilibrium. Our results suggested that HS03- ion and/or SO3 gas were likely to be important stimuli to
bronchoconstriction, but that SO3 ion was not. Finally, to determine if assessment of airway vascular permeability
or morphologic evidence of airway injury would be more sensitive indicators of the effects of acid aerosols than
is bronchoconstriction, we examined the effects of exposure to a range of atmospheres containing aerosols of HSO3-
and of HCL on these parameters in male Hartley guinea pigs. Although we were able to cause bronchoconstriction
during exposure to acid aerosols at pH 1, no exposure condition caused increased tracheal vascular permeability
or produced morphologic evidence of airway injury on light microscopy of Giemsa stained sections. We conclude that
these parameters are not likely to be sensitive indicators of the short term effects of acid aerosol inhalation.
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