Effect of rebreathing on psychomotor skills when wearing integral crash helmets.

Nine volunteer subjects underwent psychomotor testing when wearing an integral crash helmet in a variety of conditions which lead to rebreathing. There was a wide individual variation in the extent of rebreathing. In the worst conditions the minimum inspired carbon dioxide tension (PICO2) increased to 2.6 kPa. The psychomotor test was a tracking test based on a microcomputer. There was a significant deterioration in the ability to perform the test when the helmet was worn with the visor down and restricted airflow into the helmet (P = less than 0.05). In those tests when the minimum PICO2 exceeded 0.5 kPa the decrease in performance was more highly statistically significant (p = less than 0.005). Rebreathing wearing integral crash helmets results in a variable impairment in the subjects' ability to perform a tracking test. We recommend that the maximum level of CO2 retention inside integral crash helmets should not exceed 0.5 kPa minimum PICO2.