A Study on the Acute and Long-Term Effects of Hydrogen Chloride on Respiratory Response and Pulmonary Function and Morphology in the Baboon

Because of its wide acceptance as a surrogate for man, the ba boon was used to investigate the acute and long-term effects of HCl in primates and to evaluate the validity of claims that humans are much more sensitive than rodents. Four groups of three anesthetized adult male baboons (Papio cynocephalus) were exposed for 15 minutes to air (controls) or to one of three targeted concentrations of HCl, i.e., 500, 5000 or 10,000 ppm. The animals responded to the HCl atmospheres with an increase in respiratory frequency and minute volume, which appeared to be concentration-related and was statis tically significant in comparison of the 10,000 ppm HCl-exposed animals with the controls. This increased ventilatory response to high concentrations of HCl appeared to be an attempt by the animals to compensate for the rapid decrease in arterial oxygen pressure probably caused by broncho-constriction of airways of the upper respiratory tract. Pulmonary function and CO2 challenge response tests at three days and three, six, and twelve months' postexposure did not show any exposure-related, long-term effects except in the 10,000 ppm HCl-exposed animals. These results were consistent with the absence of observed effects on breathing pattern and of significant respiratory tract pathology except in ani mals exposed to 10,000 ppm HCl. The results of this study indicate that deep lung penetration of HCl in primates is minimal, except at very high concentra tions, because of the effective removal (scrubbing) of HCl by the moist oral and nasal mucosa of the upper respiratory tract.