Acidity potentiates bronchoconstriction induced by hypoosmolar aerosols.

Naturally occurring fogs are usually hypoosmolar with respect to body fluids and can be quite acidic. Because both hypoosmolarity and acidity can cause bronchoconstriction, we studied whether there was a positive interaction between these stimuli in 12 subjects with asthma. We administered the following aerosols: hypoosmolar saline (30 mOsm) at pH 5.5, 3 hypoosmolar acids (0.005 M H2SO4, 0.01 M HNO3 and a 1:1 mixture of 0.005 M H2SO4 and 0.01 M HNO3, all 30 mOsm) at pH 2, and isoosmolar 0.005 M H2SO4 (300 mOsm) at pH 2. Each aerosol was administered on a separate day and was inhaled through a mouthpiece during tidal breathing. Specific airway resistance (SRaw) was measured before and after the subjects inhaled aerosols delivered at as much as 5 doubling nebulizer outputs. For each aerosol challenge, an output-response curve was generated, and the nebulizer output required to increase SRaw by 100% above baseline (PO100) was calculated. Mean values of PO100 were significantly lower for each of the hypoosmolar acids than for hypoosmolar saline (1.65 + 0.43 g/min [mean + SEM] for saline compared with 0.95 + 0.11, 1.05 + 0.20, and 0.90 + 0.14 for H2SO4, HNO3, and a 1:1 mixture of the two; all p values less than 0.025). Mean values of PO100 did not differ among the 3 acids studied. For 7 of 12 subjects, all 3 acids caused a leftward shift in the output-response curve from the curve generated for hypoosmolar saline aerosol. Isoosmolar H2SO4 did not increase SRaw by 100% in any subjects, even at the maximal nebulizer output that delivered a concentration of H2SO4 in excess of 40 mg/m3.(ABSTRACT TRUNCATED AT 250 WORDS)