Effects of acute exposure to ozone on heart rate and blood pressure of the conscious rat.

Electrocardiogram and arterial blood pressure in conscious and unrestrained rats of various ages were recorded during a 3-hr exposure to filtered air or 1 ppm ozone (O3). In general, heart rate and mean arterial blood pressure of rats significantly decreased during exposure to O3, whereas these functional parameters remained almost stable during exposure to filtered air. Heart rate usually reached a plateau during the exposure to O3. Additionally, PR interval and QRS complex significantly increased and premature atrial contraction and incomplete A-V block were frequently observed during the exposure to O3. These circulatory effects of O3 were more markedly manifested by rats 11 weeks old than either those 8 or 4 weeks old. On the other hand, no significant difference in the circulatory responses was observed between male and female rats. These circulatory effects of O3 may be significant from the viewpoint of health effects, although its mechanisms remain unsolved.