Concentration-dependent respiratory response of guinea pigs to paraquat aerosol.

Six groups of male English smooth-haired guinea pigs were exposed to a paraquat aerosol for 4 h. Concentrations of the paraquat ion aerosols ranged from 0.83 to 2.07 mg/m3. Over 85% of the particles in the aerosol were found to be under 0.65 micron. Tidal volume and respiratory frequency of each animal were measured prior to exposure, immediately following exposure, and 18 h following exposure. These parameters were monitored during air breathing and a 10% CO2 challenge using a whole body plethysmograph fitted with a head chamber. A concentration-related decrease in tidal volume and increase in respiratory frequency were found 18 h following exposure when breathing air and the CO2 mixture. Inspection of the flow-volume (V-VT) loops showed abnormal rectangular shapes 18 h following exposure, also varying with the concentration and indicative of lung restriction with a hyperventilation pattern. This study provides quantitative information on the respiratory toxicity following a paraquat inhalation exposure and qualitative description of its effect on the respiratory pattern. The measurements made may be of value in the search of antidotes for this important herbicide.