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Coma
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Classroom Activity
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Objective
To investigate the diving reflex response that extends the amount of
time a person can stay under water.
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copy of "The Diving Reflex" student handout (PDF
or
HTML)
- dishpan filled with 8 cm (about 3 in.) of cold water
- stopwatch or clock with a second hand
- towel
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Dr. Ghajar's research shows that the way the brain responds to
head trauma has been misunderstood, and consequently treatment
methods are outdated. Similarly, the so-called
diving reflex—which extends the amount of time a
person can survive underwater by slowing the heart rate and
routing blood to vital organs—was also long misunderstood.
As a result, victims who were underwater for long periods of
time and showed no signs of life were declared dead. But, as
scientists and doctors began to understand this response,
life-saving techniques were changed and drowning victims revived
after being underwater for extended periods of time.
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Students can investigate this response in this activity. Divide
students into pairs and distribute "The Diving Reflex" student
handout.
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Have students test the diving reflex by comparing their resting
pulse to their pulse rate while their faces are submerged in
cold water for 15 seconds. Students should be seated and
submerge their faces to the hairline and in front of the ears.
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After students have completed the activity, discuss what they
thought would happen compared to what they found. Then address
why it might have been difficult to understand the diving reflex
and how new understandings led to changes in trauma treatment.
Safety Alert
Students with the following medical conditions should obtain a
doctor's permission before submerging the face in ice water for 15
seconds: moderate to severe asthma (uses an inhaler at least once a
day); cystic fibrosis or any lung disease; sinus or ear infection;
any kind of heart problems or heart disease; seizure disorder (not
controlled on medication); high blood pressure or anyone taking
blood pressure medicine. In addition, students unable to hold their
breath for 15 seconds should not participate (have students practice
before submerging). Students with conjunctivitis (pink eye), open
sores, or lesions of the mouth or face should use a separate pan of
clean water. Students afraid to submerse their faces should not be
forced to participate. Under most circumstances, this is a very safe
activity.
When students immerse their faces in cold water, their pulse rates
should decrease. To get the best results, students should perform
the experiment in a seated position and begin with a resting heart
rate and a normal body temperature. You might also add ice cubes to
the water to keep it as cold as possible. If students measure their
heart rates after, rather than during, submersion in the water, have
them keep their heads near the level of the pan so they are
measuring the reaction to cold water, not their reaction to suddenly
raising the head. The diving reflex varies among people and is most
noticeable in younger children. It slows the body's metabolism and
routes blood toward important organs, like the brain, to help keep
them functioning.
Understanding that the body could survive after being immersed
underwater for long periods of time without oxygen came only after
doctors and emergency medical technicians began to question accepted
guidelines for dealing with drowning victims. By giving CPR to
victims who had been pulled from very cold water and seeing some of
them recover without brain damage, the "accepted" guidelines (that
the brain was dead or severely damaged after only a few minutes
without oxygen) came under question. Researchers helped to link this
survival with the diving reflex and explain the seeming
contradiction, after which guidelines were revised.
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