Variability of Driving Performance During Microsleeps

This study aimed to evaluate the value of measuring microsleeps as an indicator of driving performance impairment in drowsy drivers with sleep disorders. Drivers with sleep disorders such as obstructive sleep apnea/hypopena syndrome (OSAHS) are at increased risk for driving performance errors due to microsleep episodes, which presage sleep onset. To meet this aim, the authors tested the hypothesis that OSAHS drivers show impaired control over vehicle steering, lane position and velocity during microsleep episodes compared to when they are driving without microsleeps on similar road segments. A microsleep is defined as a 3-14 sec episode during which 4-7 Hz (theta) activity replaces the waking 8-13 Hz (alpha) background rhythm. Microsleep episodes were identified in the electroencephalography (EEG) record by a neurologist certified by the American Board of Sleep Medicine. Twenty-four drivers with OSAHS were tested using simulated driving scenarios. Steering variability, lane position variability, acceleration and velocity measures were assessed in the periods during a microsleep, immediately preceding (pre) microsleep, and immediately following (post) microsleep. In line with the authors' introductory hypothesis, drivers with OSAHS did show significantly greater variation in steering and lane position during the microsleep episodes compared to the periods pre and post microsleep. The results indicate that identification of microsleep episodes can provide a marker for declining vehicle control of drivers with OSAHS.