Formaldehyde (HCHO) is a common chemical found in occupational and residential environments and has been suggested as a cause of asthmalike symptoms in some individuals. Clinical and animal studies suggest that HCHO adsorbed on respirable particles may elicit a greater pulmonary physiologic and inflammatory effect than gas-eous HCHO alone. The purpose of this study was to determine if respirable carbon particles have a synergistic effect on the acute symptomatic and pulmonary physiologic response to HCHO inhalation. We randomly exposed 24 normal, nonsmoking, methacholine-nonreactive subjects to2h each of clean air, 3 ppm formaldehyde, 0.5 mg/m3 respirable activated carbon aerosol, and the combination of 3 ppm formaldehyde plus activated carbon aerosol. The subjects engaged in intermittent heavy bicycle exercise (VE = 57 l/min) for 15 min each half hour. Measures of response included symptom questionnaires, spirometry, body plethysmography, and postexposure serial peak flows. Formaldehyde exposure was associated with significant increases in reported eye irritation, nasal irritation, throat irritation, headache, chest discomfort, and odor. We observed synergistic increases in cough, but not in other irritant respiratory tract symptoms, with inhalation of formaldehyde and carbon. Small (<5%) synergistic decreases in FVC and FEV3 were also seen. We observed no HCHO effect on FEV1; however, we did observe small (<10%) significant decreases in FEF25-75% and SCaw which may be indicative of increased airway tone. Overall, our results demonstrated synergism, but the effect is small and its clinical significance is uncertain.
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