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Coma

Classroom Activity

Objective
To investigate the diving reflex response that extends the amount of time a person can stay under water.

• 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

1. 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shows that the way the brain responds to head trauma has been misunderstood, and consequently treatment methods are outdated.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.

2. Students can investigate this response in this activity. Divide students into pairs and distribute "The Diving Reflex" student handout.

3. 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.

4. 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.