Drivers with sleep-breathing disorders
Obstructive sleep apnoea syndrome (OSAS) is a common sleep breathing disorder leading to a fragmented sleep and daytime sleepiness. There is evidence that persons with this medical condition have a higher crash risk. Terán-Santos et al  performed a case-control study that compared drivers who received hospital emergency help after a traffic crash with gender and sex matched group of patients who sought medical help for other reasons than chronic illness or a traffic crash. The analyses controlled for many factors such as alcohol use, use of medicines, body weight, and annual kilometres driven. The key result was that persons with sleep apnoea had a 6 times higher crash risk.
In a case control study, Teran-Santos et al  present findings from 102 drivers who had crashed on motorways and required emergency room treatment, compared with 152 randomly selected, primary care patients who had not crashed in the past two months. After in-home screening followed by laboratory polysomnography, it was found that those with OSAS (apnea-hypopnea index (AHI) >9.9) had an independent odds ratio of 6.2 (2.4–16.2) for having a crash. Consumption of alcohol further increased the risk of accident in those with OSAS. This study had the drawback that the cases drove around 7000km/year more than the controls, which may explain some of the increased risk observed.
In New Zealand, Yee et al  investigated sleep breathing disorders in people reporting for treatment in the Emergency Department of Wellington Hospital following a motor vehicle crash. Of a potential 120 drivers, 40 completed overnight polysomnography and sleep questionnaires. Fourteen of the 40 (35%) were found to have OSAS and 9 (22.5%) had another sleep disorder or chronic sleep restriction. Of the same sample, 15% had OSAS with an AHI of >15 – a severity that has been shown to increase the risk of motor vehicle crashes. Although this was an uncontrolled study and response rate is low, the results were comparable to the findings of Teran-Santos et al.