Evaluation of the pulmonary effects of HCl using CO2 challenges in guinea pigs

Pulmonary effects of inhalation exposures to hydrogen chloride were evaluated during and following exposure in male guinea pigs. During exposure, the respiratory rate and the time of onset of sensory or pulmonary irritation as evidenced by the change in respiratory pattern were measured. HCl inhalation resulted in both sensory and pulmonary irritation. The onset of sensory irritation took 6 min during HCl exposures at 320 ppm but less than 1 min at 680, 1040, and 1380 ppm. The onset of pulmonary irritation showed a concentration-response relationship, the higher the concentration the earlier the onset. Following exposure to HCl, animals were evaluated using a pulmonary performance test based on their ventilatory response (respiratory rate and tidal volume) during challenge with 10% CO2. The maximal respiratory frequency achieved during the CO2 challenge was lower in the HCl-exposed animals than in the controls in a HCl concentration-dependent fashion, but HCl had no apparent effect on the maximal tidal volume achieved during CO2 challenges. HCl exposure also affected baseline respiratory rate and tidal volume of the animals after exposure. Impairments of the respiratory function were also supported by evidence of morphological injury in both the airways and the alveolar region.