A new guinea-pig model for acute inhalation studies on combined effects of cold air and pollutants

Abstract

We have developed a new small animal model for acute inhalation studies on combined effects of cold air and gaseous urban air pollutants. The anaesthetised, tracheostomised and paralysed guinea-pig was placed inside a small, sealed whole-body-box, in which it was ventilated mechanically by using cyclic negative pressure (P box) for active expansion of the chest. During a 2-h normal ventilation with warm humid air ( n=6), there was a need for increasing P box with time to maintain the fixed tidal volume (V t) of 11 ml/kg. No such need was seen in the experiments with 15-min periods of isocapnic hyperventilation at 80 and 120 breaths/min ( n=13). During the 2-h normal ventilation and in experiments with hyperventilation, there was a gradual increase in heart rate and small gradual decreases in Pa CO 2 and pH with time. Cold air+SO 2 2.5 ppm produced a significantly stronger bronchoconstriction (ΔV t=−30.3±7.2%, n=6, P<0.05) than clean cold dry air (ΔV t=−10.6±1.3%, n=6) and cold air+NO 2 2.5 ppm (ΔV t=−13.2±3.3%, n=6), although these three exposure conditions produced similar decreases in tracheal air and retrotracheal tissue temperatures. With the present guinea-pig model, the combined respiratory effects of cold air and gaseous urban air pollutants can be investigated in a highly controlled manner.