Development of a large-scale computer-controlled ozone inhalation exposure system for rodents

Complete systems for laboratory-based inhalation toxicology studies are typically not commercially available; therefore, inhalation toxicologists utilize custom-made exposure systems. Here we report on the design, construction, testing, operation, and maintenance of a newly developed in vivo rodent ozone inhalation exposure system. Key design requirements for the system included large-capacity exposure chambers to facilitate studies with large sample sizes, automatic and precise control of chamber ozone concentrations, as well as automated data collection on airflow and environmental conditions. The exposure system contains two Hazelton H-1000 stainless steel and glass exposure chambers, each providing capacity for up to 180 mice or 96 rats. We developed an empirically tuned proportional-integral-derivative (PID) control loop that provides stable ozone concentrations throughout the exposure period (typically 3h), after a short ramp time (∼8 minutes), and across a tested concentration range of 0.2 to 2 ppm. Specific details on the combination analog and digital input/output system for environmental data acquisition, control, and safety systems are provided, and we outline the steps involved in maintenance and calibration of the system. We show that the exposure system produces consistent ozone exposures both within and across experiments, as evidenced by low coefficients of variation in chamber ozone concentration and consistent biological responses (airway inflammation) in mice, respectively. Thus, we have created a large and robust ozone exposure system, facilitating future studies on the health effects of ozone in rodents.