Teach them a lesson they'll never forget! The Diving Response Lab...

Data acquisition hardware used: PowerLab 26T

Data analysis software used: Lt: Life Science teaching software / LabChart

Set up your equipment to record signals

Finger pulse transducers are often very sensitive to movement. The volunteer should try to keep the finger still when recording data.

The question here is: "What is the effect of breath holding on heart rate and peripheral circulation under normal conditions?"

For all activities in this lab use exactly the same position when taking measurements. It is best for the volunteer to stand upright facing the "diving tub" and bend from the waist when lowering the face. Taking each measurement while the volunteer is in the same position will decrease experimental variability.

Procedure

1. Set your data analysis software to record average pulse rate and amplitude.
2. Fill a tub with cool water (10–15°C, 50–60°F) and monitor the water temperature with a thermometer. If required, use ice to chill the water.
3. Position the volunteer as shown above, with the face just above the water's surface. The volunteer should remain motionless.
4. Select Start on your data analysis software to begin recording average pulse rate and amplitude. Record the volunteer's resting pulse for 30 s. Note this section on the recording as “Resting”.
5. After 30 s, ask the volunteer to take a deep breath, exhale partially, and then hold the breath. The volunteer should remain in position just above the water. Note this section on the recording as “Breath holding”.
6. Record for a minimum of 30 s while the volunteer is breath holding. One member of the group should tap the volunteer on the back at 10 s intervals to help keep track of the time and prevent anxiety.
7. After 30 s tell the volunteer to resume breathing. Make sure the volunteer remains still. Note this on the recording as “Recovery”.
8. After 30 s, stop the recording.

Analysis

Here, students examine how breath holding affects pulse rate and amplitude.

1. On the recording, select a representative 5 s after the "Resting" comment. Note the average pulse rate and amplitude.
2. Repeat for the first 5 s of breath-hold.
3. Repeat for the last 5 s of breath-hold.
4. Repeat for a representative 5 s at the end of recovery.

The question here is: "What is the effect of breath holding on heart rate and peripheral circulation during a simulated dive?"

Procedure

1. Ensure your data analysis software is recording average pulse rate and amplitude.
2. Ask the volunteer to stand in front of the tub, bent over so that the face is just above the water's surface, and remain motionless.
3. Select Start on your data analysis software to record. Note this on the recording as “Resting”.
4. After 30 s, ask the volunteer to take a deep breath, exhale partially, then hold his or her breath and immerse their face up to the cheeks in the tub of water. Note this on the recording as “Dive”.
5. Record for a minimum of 30 s while the volunteer is submerged. One member of the group should tap the volunteer on the back at 10 s intervals to help keep track of the time and prevent anxiety. Do not force the volunteer to remain submerged if he or she is not comfortable!
6. After 30 s tell the volunteer to surface, and return to the original position with their face just above the water surface. Make sure the volunteer remains still to minimize movement artifacts. Note this on the recording as “Recovery”.
7. After 30 s stop the recording.

Analysis

Here students examine how a "dive" affects pulse rate and amplitude.

1. On the recording, select a representative 5 s after the "Resting" comment.     
   Note the average pulse rate and amplitude.
2. Repeat for the first 5 s of breath-hold.
3. Repeat for the last 5 s of breath-hold.
4. Repeat for a representative 5 s at the end of recovery.

Ask some questions to check student’s understanding

Here are some questions you could ask your students to test their understanding:

• Did you observe any changes in heart rate during and after the simulated dive?
• Describe any changes in pulse amplitude you observed during the simulated dive. Explain why these changes occurred.
• Compare the effects of diving and breath holding on pulse rate. Were they the same?
• How long did the diving response take to occur? How quickly did the heart rate return to normal after a dive?
• What environmental factors could explain differences between breath holding and a "dive"?
• Compare the changes in heart rate during dives among the members of other groups. Is the effect between individuals similar?

The question here is: "Does peripheral blood flow change during the dive response?"

Many changes in cardiovascular function occur during the diving response. In this activity students use an indirect method to detect changes in peripheral blood flow. They will investigate the effects of venous occlusion to the leg by applying a thigh blood pressure (sphygmomanometer) cuff to occlude the venous return of blood from the leg, and then removing it to measure changes in leg volume with a respiratory belt transducer.

Equipment setup

Both the sphygmomanometer cuff and the respiratory belt transducer can be placed over clothing.

Procedure

This activity examines how leg volume changes after a blood pressure cuff is removed.

Students will perform three protocols:     
1. Control with normal breathing - Control Protocol     
2. During a simulated dive - Dive Protocol     
3. During breath holding alone - Breath-Hold Protocol

1. Set your analysis software to record leg volume in arbitrary units (au).
2. Place the blood pressure cuff around the volunteer's thigh.
3. Ask the volunteer to stand in front of the diving tub, bent over so that the face is just above the water's surface, and remain motionless.
4. Call this recording “Control Protocol".
5. Begin recording on your data analysis software. Note this section of the recording as “Resting”.
6. Inflate the blood pressure cuff rapidly to 60 mmHg. Tighten the valve to maintain this pressure for the 30 s protocol. Note this section of the recording as “Cuff Inflated”.
7. 20–25 s into the protocol, the assistant should rapidly remove the cuff. The volunteer should stay still and remain in the same position. Note this section of the recording as “Cuff Removed”.
8. 30 s into the protocol, the volunteer should stop the protocol. His or her face should remain just above the water's surface.
9. Note this section of the recording as “Recovery” . Record for 10 more seconds, then stop the recording.
10. Release the valve and squeeze the air out of the cuff.

Repeat steps 1–10 for the remaining 2 protocols, naming the relevant recording "Dive Protocol" and "Breath-Hold Protocol".

Analysis

Here students will analyze the effects of venous occlusion to the leg.

1. Look at the "Control Protocol" recording.
2. Mark the point where the cuff is ripped off the leg, and place your point selector at the point of maximum deflection.
3. The leg volume will be shown in arbitrary units (au).
4. Repeat steps 1–3 for:
   • Dive Protocol
   • Breath-Hold Protocol

Ask some questions to check student’s understanding

Here are some questions you could ask your students to test their understanding:

• Do your results for leg volume suggest that peripheral circulation changes during a "dive"?
• Do your results for leg volume suggest that peripheral circulation changes during a breath-hold?
• Based on your data, describe the potential advantages and disadvantages of the diving response. What other factors should be accounted for during a real dive that were not simulated in this activity?