Brake reaction time--effects of age, sex, and carbon monoxide.

Simulated braking responses have been tested in relation to blood carboxyhemoglobin (HbCO) levels. The main determinants of percentage of HbCO in 352 subjects attending a fall fair were daily cigarette consumption and minutes since the last cigarette. In women the brake response time deteriorated from age 16 yr, but in the men there was an improvement from age 16 to the early 20s. Times at all ages were better for men than for women. Average response times and the rate of aging of the braking response were very similar in smokers and in nonsmokers. In the nonsmokers, however, response time with step function CO increments of as much as 7% HbCO. There was a suggestion of a small increase of reaction time, with an opposing decrease of leg movement time, during the first few minutes after CO exposure; nevertheless, these trends were statistically insignificant.