Research Projects

Project at a Glance

Project Status: complete

Title: Roles of pH, titratable acid and specific chemical composition in mediating effects of acid aerosols on the airways

Principal Investigator / Author(s): Sheppard, Dean

Contract Number: A4-113-32


Research Program Area: Atmospheric Processes

Topic Areas: Acid Deposition


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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