Inhalation studies of Mt. St. Helens volcanic ash in animals: respiratory mechanics, airway reactivity and deposition.

Effects of fine volcanic ash aerosol on pulmonary mechanical properties of awake guinea pigs were evaluated during exposure by inhalation. Ash penetration into the lung as well as tissue response to ash were determined by transmission electron microscopy. The reactivity of airway epithelial irritant receptors following ash exposure was assessed using a histamine bronchoprovocation test. Results indicated that breathing 9,4 mg/m3 of ash for 2 hr did not cause a measurable change in pulmonary function of guinea pigs. Electron micrographs showed that ash particles in the lung below the hilus did not seem to produce any acute tissue reaction and were almost all phagocytized by macrophages. Airways of guinea pigs exposed to ash were significantly less responsive to histamine than were the airways of animals exposed only to air. It appears that even though Mt. St. Helens ash was well tolerated by the guinea pig during the exposure, its presence in the inhaled air did change the "histamine sensitivity" of airway epithelial irritant receptors.