Sleep deprivation and its effects: from Matthew Walker

Another very interesting quote from Matthew Walker‘s new book named “Why We Sleep“, this time about sleep deprivation and its effects:

Struck by the weight of damning scientific evidence, the Guinness Book of World Records has stopped recognizing attempts to break the sleep deprivation world record. Recall that Guinness deems it acceptable for a man (Felix Baumgartner) to ascend 128,000 feet into the outer reaches of our atmosphere in a hot-air balloon wearing a spacesuit, open the door of his capsule, stand atop a ladder suspended above the planet, and then free-fall back down to Earth at a top speed of 843 mph (1,358 kmh), passing through the sound barrier while creating a sonic boom with just his body. But the risks associated with sleep deprivation are considered to be far, far higher. Unacceptably high, in fact, based on the evidence.

There are many ways in which a lack of sufficient sleep will kill you. Some take time; others are far more immediate. One brain function that buckles under even the smallest dose of sleep deprivation is concentration. The deadly societal consequences of these concentration failures play out most obviously and fatally in the form of drowsy driving. Every hour, someone dies in a traffic accident in the US due to a fatigue-related error. There are two main culprits of drowsy-driving accidents. The first is people completely falling asleep at the wheel. This happens infrequently, however, and usually requires an individual to be acutely sleep-deprived (having gone without shut-eye for twenty-plus hours). The second, more common cause is a momentary lapse in concentration, called a microsleep. These last for just a few seconds, during which time the eyelid will either partially or fully close. They are usually suffered by individuals who are chronically sleep restricted, defined as getting less than seven hours of sleep a night on a routine basis. During a microsleep, your brain becomes blind to the outside world for a brief moment—and not just the visual domain, but in all channels of perception. Most of the time you have no awareness of the event. More problematic is that your decisive control of motor actions, such as those necessary for operating a steering wheel or a brake pedal, will momentarily cease. As a result, you don’t need to fall asleep for ten to fifteen seconds to die while driving. Two seconds will do it. A two-second microsleep at 30 mph with a modest angle of drift can result in your vehicle transitioning entirely from one lane to the next. This includes into oncoming traffic. Should this happen at 60 mph, it may be the last microsleep you ever have.

David Dinges at the University of Pennsylvania, a titan in the field of sleep research and personal hero of mine, has done more than any scientist in history to answer the following fundamental question: What is the recycle rate of a human being? That is, how long can a human go without sleep before their performance is objectively impaired? How much sleep can a human lose each night, and over how many nights, before critical processes of the brain fail? Is that individual even aware of how impaired they are when sleep-deprived? How many nights of recovery sleep does it take to restore the stable performance of a human after sleep loss? Dinges’s research employs a disarmingly simple attention test to measure concentration. You must press a button in response to a light that appears on a button box or computer screen within a set period of time. Your response, and the reaction time of that response, are both measured. Thereafter, another light comes on, and you do the same thing. The lights appear in an unpredictable manner, sometimes in quick succession, other times randomly separated by a pause lasting several seconds. Sounds easy, right? Try doing it for ten minutes straight, every day, for fourteen days. That’s what Dinges and his research team did to a large number of subjects who were monitored under strict laboratory conditions. All of the subjects started off by getting a full eight-hour sleep opportunity the night before the test, allowing them to be assessed when fully rested. Then, the participants were divided into four different experimental groups. Rather like a drug study, each group was given a different “dose” of sleep deprivation. One group was kept up for seventy-two hours straight, going without sleep for three consecutive nights. The second group was allowed four hours of sleep each night. The third group was given six hours of sleep each night. The lucky fourth group was allowed to keep sleeping eight hours each night. There were three key findings. First, although sleep deprivation of all these varied amounts caused a slowing in reaction time, there was something more telling: participants would, for brief moments, stop responding altogether.

Slowness was not the most sensitive signature of sleepiness, entirely missed responses were. Dinges was capturing lapses, otherwise known as microsleeps: the real-life equivalent of which would be failing to react to a child who runs out in front of your car when chasing a ball. When describing the findings, Dinges will often have you think of the repeating beep from a heart monitor in a hospital: beep, beep, beep. Now picture the dramatic sound effect you hear in emergency room television dramas when a patient starts to slip away as doctors frantically try to save their life. At first, the heartbeats are constant—beep, beep, beep—as are your responses on the visual attention task when you are well rested: stable, regular.

Switch to your performance when sleep-deprived, and it is the aural equivalent of the patient in the hospital going into cardiac arrest: beep, beep, beep, beeeeeeeeeeeeeep. Your performance has flatlined. No conscious response, no motor response. A microsleep. And then the heartbeat comes back, as will your performance—beep, beep, beep—but only for a short while. Soon, you have another arrest: beep, beep, beeeeeeeeeeeeeep. More microsleeps. Comparing the number of lapses, or microsleeps, day after day across the four different experimental groups gave Dinges a second key finding. Those individuals who slept eight hours every night maintained a stable, near-perfect performance across the two weeks. Those in the three-night total sleep deprivation group suffered catastrophic impairment, which was no real surprise. After the first night of no sleep at all, their lapses in concentration (missed responses) increased by over 400 percent. The surprise was that these impairments continued to escalate at the same ballistic rate after a second and third night of total sleep deprivation, as if they would continue to escalate in severity if more nights of sleep were lost, showing no signs of flattening out. But it was the two partial sleep deprivation groups that brought the most concerning message of all. After four hours of sleep for six nights, participants’ performance was just as bad as those who had not slept for twenty-four hours straight—that is, a 400 percent increase in the number of microsleeps.

By day 11 on this diet of four hours of sleep a night, participants’ performance had degraded even further, matching that of someone who had pulled two back-to-back all-nighters, going without sleep for forty-eight hours. Most worrying from a societal perspective were the individuals in the group who obtained six hours of sleep a night—something that may sound familiar to many of you. Ten days of six hours of sleep a night was all it took to become as impaired in performance as going without sleep for twenty-four hours straight. And like the total sleep deprivation group, the accruing performance impairment in the four-hour and six-hour sleep groups showed no signs of leveling out. All signs suggested that if the experiment had continued, the performance deterioration would continue to build up over weeks or months. Another research study, this one led by Dr. Gregory Belenky at Walter Reed Army Institute of Research, published almost identical results around the same time. They also tested four groups of participants, but they were given nine hours, seven hours, five hours, and three hours of sleep across seven days.

This coming week, more than 2 million people in the US will fall asleep while driving their motor vehicle. That’s more than 250,000 every day, with more such events during the week than weekends for obvious reasons. More than 56 million Americans admit to struggling to stay awake at the wheel of a car each month. As a result, 1.2 million accidents are caused by sleepiness each year in the United States. Said another way: for every thirty seconds you’ve been reading this book, there has been a car accident somewhere in the US caused by sleeplessness. It is more than probable that someone has lost their life in a fatigue-related car accident during the time you have been reading this chapter.

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