A sleep-deprived clinician
recently sent an email to a friend. He was responding to comments about an
article he had written only three months earlier. “When did I do that one?”
the clinician wrote. “What day is it? Where am I?” The clinician had toiled
in medicine for decades, but he was only half-kidding. After weeks on a grueling
rotation, he felt the way virtually every reader of this newsletter has felt:
Things weren’t clicking: the twilight zone between the ears was cotton-ball
medicine’s contribution to sleep deprivation may be rivaled only by that of
the military’s, well-controlled research on sleep deprivation and cognitive
performance is appallingly rare. How do the body and mind perform after week
upon week of sleep-stunted nights? How do they perform without any sleep at all?
Amazingly, there is a lot of disagreement.
recent study brings new rigor to answering these questions. It suggests that if
you regularly sleep six hours or less per night, you are paying dearly for it
(and, perhaps, your patients are too). And, like your lay counterparts driving
trucks and moonlighting in doughnut shops, you are probably too impaired to know
P.A. Van Dongen, PhD, et al. from the University of Pennsylvania randomized 48
healthy adults to one of three sleep doses (four, six, or eight hours per night)
for 14 consecutive days or to total sleep deprivation (three nights without
sleep). Prior to the study, the subjects normally slept 7.6 to 7.9 hours per
night. (See Van Dongen et al., 2003).
past studies, which found few detrimental effects of sleep deprivation, this
study was conducted in a laboratory. Sleeping periods, waking activities, and
diet were carefully controlled. The researcher performed neurobehavioral
assessments every two hours of wakefulness. They measured reaction times to a
random stimulus (“psychomotor vigilance”), time required to match numbers to
geometric shapes, time to complete 50 arithmetic problems and sleepiness. They
also measured subjects’ “sleep architecture” using polysomnography tests.
result: “Sleep periods chronically limited to four hours and six hours per
night progressively eroded the effectiveness of psychomotor vigilance
performance, working-memory performance and cognitive performance,” according
to Van Dongen et al. The more days the sleep deprivation lasted, the worse
who slept four hours per night for two weeks had cognitive impairments equal to
those who went two days without any sleep. Subjects who slept six hours per
night for two weeks reached levels of impairment equivalent to those who went
one night without any sleep.
research challenges a few longstanding beliefs in the scientific and lay
communities. It suggests, for starters, that people do not adjust to sleep
deprivation-even if they feel otherwise. “Surprisingly, by the end of the 14
days of sleep restriction when performance was at its worst levels, subjects in
the four-hour and six-hour sleep period conditions reported feeling only
slightly sleepy,” note Van Dongen et al.
study also undermines the “core sleep” hypothesis – which posits that
humans need only six hours of sleep to repair “wear and tear” on the
cerebrum and preserve satisfactory daytime functioning and that any sleep beyond
six hours serves mostly to while away the tedium of darkness.
the study also dispels the myth (already dismissed by many a surgical and
medical resident) that youth is protective against these cognitive deficits. The
participants in this trial were healthy adults 21 to 38 years of age.
the ideal amount of sleep? Eight hours. “Cumulative wakefulness beyond 15.84
hours predicted performance lapses across all experimental conditions,” the
important caveat should be added to these conclusions. The subjects in this
study were deprived of exercise, stimulants (Caffeine, etc.) and naps during the
entire period of the study. The authors did not explore the extent to which
these might attenuate cognitive deficits caused by chronic sleep deprivation.
Dongen HPA et al. The cumulative cost of additional wakefulness: Dose response
effects on the neurobehavioral functions and sleep physiology from chronic sleep
restrictions and total sleep deprivation, Sleep, 2003: 26(2): 117-26.