Pathophysiologic Responses of Sheep to Brief High-Level Nitrogen Dioxide Exposure

Abstract

The cardiopulmonary response to short-duration, high-concentration nitrogen dioxide (NO₂) exposure was examined in conscious domestic sheep (Ovis aries). Six intubated animals in each of 3 groups were given a 15-min exposure to either air (control) or approximately 700 or 500 ppm NO₂₋ Pulmonary and systemic hemody-namics, pulmonary mechanics, blood gases, and hematologic variables were measured immediately before and after exposure and at 1, 4, and 24 h after exposure. Minute ventilation was monitored during exposure, and a pulmonary histopathologic examination was performed 24 h postexposure. Negligible effects were observed in the control group. Exposure to 100 ppm NO₂ caused a modest increase in minute ventilation during exposure, and an increased number of leukocytes was found within interalveolar capillaries upon histologic examination. Exposure to 500 pprn NO₂ induced an immediate and profound lung irritant response characterized by an increase in lung resistance, respiratory rate, and minute ventilation. The exposure was marked by a statistically significant, but small, increase in methemoglobin concentration. Pulmonary function progressively deteriorated in the 24-h period following exposure to 500 ppm NO₂, and a significant arterial oxygen tension reduction and pulmonary artery pressure increase occurred at 24 h postexposure. Histologic examination after 500 ppm NO₂ revealed patchy lobular exudation and accumulation of leukocytes in both alveolar sacs and interalveolar capillaries.