To investigate the diving reflex response that extends the amount of time a person can stay
- copy of "The Diving Reflex" student handout
- dishpan filled with 8 cm (about 3 in.) of cold water
- stopwatch or clock with a second hand
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has been misunderstood, and consequently treatment methods are outdated.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.
Students can investigate this response
in this activity. Divide students into pairs and
distribute "The Diving Reflex" student handout.
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.
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
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.