Effects of inhaled acids on airway mucus and its consequences for health.

The high molecular fractions, i.e., greater than 100,000 dalton, are found to be most responsible for the H+ ion absorption capacity of the mucus in the respiratory tract. This function serves as a protection against the penetration of the H+ ion to the surrounding tissue. Acidifying mucus with a high concentration of protein, mainly glycoproteins, results in increased viscosity, which affects various lung functions. After acid saturation of the mucus, the H+ ion will react with the epithelial tissue, which results in increased permeability and a variety of effects. Acidic mucus or mucus with a low protein concentration, as in some asthmatics, constitutes a base for risk groups regarding acidic exposures. A rough estimate indicates that persons with normal mucus buffer capacity and protein content can tolerate about 3000 micrograms SO2/m3 or 300 micrograms H2SO4/m3 per 30 min.