Latest posts by Michael Morgenstern, MD (see all)
It was a routine February morning for Sam, a high school student attending a private school in upper Manhattan. Little did Sam know his life would never be the same. He woke up at 6:30 AM and boarded the school bus. Traffic was moving at a good pace on the FDR, the local highway. Listening to his favorite song playing on the radio, he wasn’t thinking about the thousands of drivers on the road that morning. If some of those drivers underwent an electroencephalogram (EEG), an electrical study of the brain, it would show something unexpected. That while driving their cars, with their eyes wide open and appearing to be wide awake, they would actually be experiencing transient episodes of microsleep. Suddenly, Sam’s school bus swerved, crashing into the guardrail separating it from oncoming traffic. Sam’s life flashed before his eyes. The bus projected upwards and was now upside-down in mid-air heading towards oncoming traffic traveling well over 50 miles an hour. What was once a school bus was now a deadly, airborne, 5000 pound projectile carrying Sam and several other students whose entire future was now uncertain.
Driver sleepiness is estimated to be responsible for nearly 1 million car accidents, 5,000 deaths and 250,000 injuries a year. It is responsible for nearly one sixth of all accidents.1 Surveys of American drivers, show nearly half admit to drowsy driving. Nearly one in four admit to falling asleep at the wheel. If you consider the occurrence of microsleep, this number increases. Nearly 250,000 people each day are estimated to fall asleep at the wheel. Many are not aware that they are microsleeping. Microsleep is a short transitional state between being asleep or awake that may last fractions of a second to several seconds long. Drivers who experience microsleep are seldom aware of its occurrence. They feel as though they “spaced out.” They may be driving with their eyes wide awake, but an electrical study of their brain will show brain waves identical to those found during sleep. Drivers that are drowsy may experience long and frequent episodes of microsleep. Repetitive head nodding, eye closure, changes to normal blinking, slow eye movements and slow head movements can also be observed in microsleepers. Microsleep events dramatically increase the likelihood of a car accident taking place.
Microsleep in Sleep Apnea
Microsleep is common in individuals with sleep apnea or sleep deprivation. Even when they get enough hours of sleep, individuals with sleep apnea lack quality sleep leading to a state of chronic sleep deprivation. Drivers who have symptoms from obstructive sleep apnea are, therefore, 2 to 4 times more likely to have a car accident than those without sleep apnea. As sleep deprivation plays a large role in the appearance of microsleep during driving, the quantity of sleep is also important. Obtaining enough sleep, around 7.5 hours each night is important. Research looking at performance measured through reaction times has also shown that sleep deprivation can have a cumulative effect. If you miss one hour of sleep one night your performance will decrease. But this performance deterioration will get worse with each additional night of sleep deprivation. So someone who loses an hour of sleep for six nights performs much worse than they would missing an hour of sleep for only one night.
Microsleep in drivers
Driving performance deteriorates and accidents increase during microsleep episodes. The total number and average length of microsleep episodes also correlates with increased accident rates. More accidents take place if there are more microsleeps. Similarly, longer episodes of microsleep increase the risk of an accident. Drivers with microsleep are prone to sway out of their lane, especially when the road curves. One study using a computer algorithm to determine the number and duration of microsleep episodes on normal sleep deprived drivers found a large number of microsleep episodes and “crashes.” They were monitored while driving in a simulator for 40 minute intervals during the hours of 1 AM and 7 AM. They were not allowed to nap. As the night progressed, the average number and length of microsleep increased. At 1:00 AM an average of 40 microsleep episodes were detected. The average length was 5 seconds and no crashes took place. By 7:00 AM the average number of microsleeps increased to 140, with an average length of 8 seconds per episode. They were also associated with a large number of “crashes.” Another observation was that in the minute leading up to each crash, a high frequency of microsleep episodes were taking place. These microsleeps occupied more than half of the minutes leading up to the crashes (not consecutively). Other studies show microsleep takes place at a much lower frequency in less sleep deprived individuals. One study examining driving in only partially sleep deprived individuals during the daytime showed events occurred only about 1 time on average, during a thirty minute drive. However, that study used much stricter criteria to define microsleep. The actual number of microsleep taking place in sleep deprived individuals is probably somewhere in between the 1 & 140 times per drive reported in the above studies. Both studies emphasize that microsleep events are dangerous and require our attention.
Stopping microsleep or its adverse consequences may include preventing it and reducing sleepiness. Increasing detection of events can also help. Automatic sleeping event sensors can trigger an alarm to alert an individual when its time to stop driving. Prevention should focus on routinely getting enough sleep and avoiding driving when drowsy. Studies show that individuals self report of drowsiness correlates with the number of episodes of microsleep. So if someone feels sleepy, they should not drive. Repeatedly feeling sleepy during the daytime may be a sign of a more serious medical disorder. It should precipitate a conversation with a doctor or sleep specialist. If you must drive in the middle of the night, shorter drives with less monotony, frequent breaks and napping may also be helpful. Caffeinated beverages such as coffee can also help reduce the frequency of microsleep. Numerous technologies also exist or are in development to detect sleepy drivers. These technologies can warn drivers if they detect behavior or driving indicating a lack of control that may be associated with microsleep. Futuristic cars that are designed with lane control and auto-breaking features can also help mitigate accidents resulting from sleepy drivers. These technologies essentially aim to automatically drive cars. Of course, if cars drive themselves the problem of microsleep during driving may become obsolete. Avoiding driving altogether when feeling tired or sleepy is probably the best policy. I often reinforce this at visits with sleep medicine patients.
Microsleep & sleep
Sleep is usually determined based on 30 second intervals in a sleep laboratory. An electroencephalogram or EEG is used to examine brain waves. As one is falling asleep, brain waves slow down. If sleep waves are present for 15 seconds of a 30 second epoch, sleep is said to be present. But people who are falling asleep have these sleep waves show up for shorter intervals, which define microsleep. They may intrude into wake states for a split second. Eventually, when trying to fall asleep, brain waves progress towards full sleeping stages. The patterns that are associated with different stages of sleep such as light sleep, deep sleep or REM sleep are also seen on EEG. Microsleep isn’t a problem when you are sleeping at night. It isn’t routinely scored during sleep studies because it isn’t consequential if you sleep for 2 seconds at night. But if you are driving a car, even a half-a-second snooze can be a big problem.
A 5000 pound projectile
Sam’s life was flashing before him. The bus was upside down, vertical and airborn flying towards oncoming traffic. Suddenly, a big bang sounded and then Sam was in severe pain. The bus had landed on a car with three passengers. The driver of the bus was killed instantly. Miraculously, the bus bounced off of the car and was propelled upright and out of the way of oncoming traffic. Sam was brought to Columbia University Medical Center and found have a broken Jaw. The other students on the bus all survived, though two others had serious injuries. The driver and passengers of the car were injured but expected to make a full recovery. Sam survived the crash, though his jaw was wired shut for the next 4 weeks. The cause of the incident was never determined, but microsleep has been suspected for many similar accidents.
Microsleep is a common phenomenon that may affect up to 250,000 drivers every day. It is estimated to contribute to nearly 1 million car accidents annually, resulting in numerous injuries and death. Getting enough quality sleep is important to prevent microsleep from taking place while driving. Sleepy drivers may experience episodes of driving asleep. If you feel too sleepy to drive, then don’t. It is always better to be safe than sorry.
1. Based on 2013 statistics of the Department of Transportation and estimates of 1/6th car accidents attributed to sleepiness.Actual numbers are 5,687,000 accidents (947,833 sleep related), 1,591,000 injuries (265,166 sleep related), 30,057 fatalities (5009 sleep related).
2. Sam’s story is based on a true story. Sam’s real name was changed but the events that took place are real.