Effects of methyl methacrylate monomer vapors on respiration and circulation in unanesthetized rats

A study was conducted in which two groups of female rats were exposed to vaporized MMA-m for a period of 20 minutes daily for 21 and 42 days, respectively. Systolic blood pressure, heart rate, respiration, and ECG were monitored for 5 minutes prior to MMA-m exposure and then during a 20-minute exposure to MMA-m. On the twenty-first and forty-second day, respectively, the aforementioned vectors were monitored again. During the first exposure 63% of the experimental animals displayed marked changes in respiration ranging from a modified Cheyne-Stokes type to periods of very shallow breathing followed by deep breathing. Thirty-eight percent showed ECG changes ranging from premature ventricular contractions and altered QRS complexes to markedly depressed T waves. Continued exposure resulted in an initial decrease followed by an increased systolic blood pressure with an increased respiratory and heart rate. At the final testing period all animals showed abnormal respiratory patterns and ECG changes and demonstrated a heart block pattern. In all animals systolic blood pressure increased the longer they were exposed to MMA-m.