Sleep impacts reaction
time as much as alcohol
BY MITCH LESLIE
You'd get very concerned
if, while waiting to board an airplane, you saw the pilot
stumble out of the airport bar. New Stanford research
suggests that you should be just as worried if you see
the pilot yawning and rubbing his eyes.
In a test of reaction
times, people who were tired because of disrupted sleep
performed about as poorly as subjects who were legally
drunk, the researchers report. The study is the first to
show severe impairment in people who have only mild to
moderate sleep disturbances.
Nelson B. Powell, DDS, MD,
leader of the research team, said he hopes that the
results will stimulate a discussion about the need for
safety guidelines to cover sleepiness -- rules that might
resemble those already in place for blood alcohol levels.
Alcohol's slowing effect
on reaction times is well documented, said Powell, who is
co-director of the Stanford Sleep Disorders Clinic and
Research Center. That is one reason why society demands
that people responsible for the safety of others -- truck
drivers, train engineers, airline pilots -- limit their
alcohol consumption before working.
Yet, Powell noted, society
does not seem to be as concerned about the harmful impact
of sleeplessness, even though fatigue contributed to
almost every high-profile accident in recent memory, from
the grounding of the Exxon Valdez to the Chernobyl and
Three Mile Island nuclear accidents.
Powell wants to see that
change, so he and five colleagues set out to measure how
the disorder known as sleep apnea affects reaction times.
People with sleep apnea -- about 24 percent of
middle-aged men and 9 percent of middle-aged women --
stop breathing multiple times during the night. These
interruptions come during sleep, so the patient may not
be aware of them, but they prevent the body from settling
into a deep, relaxing sleep and result in daytime
drowsiness.
Those with extreme apnea,
who are often so tired that they may struggle to remain
awake during a conversation or while driving to the
corner store, clearly represent a danger. However,
Powell's group wanted to learn if less severe forms of
the disorder might also compromise safety.
So they recruited 113
patients with mild to moderate sleep apnea and compared
their reaction times with those of 80 normal volunteers
who had slept well the three previous nights. Members of
the latter group took the reaction-time test sober to
provide baseline data. Then they gradually got drunk and
performed the test three additional times: once at a
blood alcohol level of 0.057 percent, again at 0.08
percent, and finally at 0.083 percent.
A blood alcohol level of
0.057 percent exceeds the legal limit for driving a
commercial vehicle, which is 0.04 percent, but falls
short of the limit to drive a car in California and many
states, which is 0.08 percent.
Comparing the two groups
on seven measures of reaction time -- including average
time, maximum time, and average of the ten fastest times
-- showed a surprising degree of impairment in the apnea
patients. On all seven measures, their results were worse
than those of the drinking group at a blood alcohol level
of 0.057 percent (see graph on page 7). And on three
measures, the apnea patients scored as badly or worse
than the drinkers who were legally drunk. "That
really stunned us," Powell said.
Taking one example, the
average reaction time for the drinkers with a blood
alcohol level of 0.057 percent was 263 milliseconds (just
over a quarter of a second), which increased to 276
milliseconds by the time their alcohol level rose to 0.08
percent. The average time for the apnea patients was 266
milliseconds.
One of Powell's
co-authors, David F. Dinges, PhD, a psychiatry professor
at the University of Pennsylvania, developed the
computerized reaction-time test for NASA as a way to
evaluate pilots and astronauts. The 10-minute test is
straightforward: the subjects push a button whenever a
red light flashes. The length of time between flash and
push is the reaction time.
Powell cautioned that he
isn't proposing specific safety guidelines. But he hopes
this study will start a national discussion and debate
about whether such rules are necessary. For example, he
suggested that it might be prudent to require airline
pilots to pass a reaction-time test before they are
allowed to fly. Alternatively, we might want to consider
monitoring their sleep to ensure they are well rested
when they sit down in the cockpit.
"Being arrested for
sleepiness -- that isn't going to happen, but maybe it
should," Powell said. "It might make people in
sensitive positions take responsibility."
Further research could
focus on other ways in which mental or physical abilities
suffer in the sleep deprived, Powell suggested. "I
am showing you just one measure of abnormality in
performance," he said.
The group's results appear
in the October issue of the journal Laryngoscope.
Powell's Stanford
colleagues on the paper are both from the Sleep Disorders
Clinic and Research Center: Robert W. Riley, DDS, MD,
associate clinical professor of psychiatry and behavioral
sciences, and Christian Guilleminault, MD, professor of
psychiatry and behavior sciences. The remaining authors
are Marc B. Blumen, MD, an assistant professor of
otolaryngology at Hopital Foch in Suresnes, France; and
Kenneth B. Schechtman, PhD, an associate professor of
biostatistics at Washington University School of Medicine
in St. Louis, Mo. SR
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