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Diving Reflex Lab

Diving Reflex Lab

Experiment HH-5: The Diving Reflex

Background
Some air-breathing animals have developed physiological and biochemical mechanisms that allow them to survive while submerged underwater for long periods of time. Animals, like sperm whales and some species of amphibians and reptiles, utilize oxygen in a more efficient manner.

Even though different species have different diving capacities, the solutions to the problems associated with diving are similar. Animals can extend diving time by: using stored oxygen; decreasing oxygen consumption; using anaerobic metabolism; and, using aquatic respiration, if possible.

A prominent method for an animal to conserve oxygen while diving is known as selective peripheral vasoconstriction. This method insures that oxygen is delivered to organs with the highest priority need for oxygen, like the brain, heart, and adrenal glands. The remaining organs subsist on local stores of oxygen or use anaerobic metabolism. Since the vasoconstriction that takes place in this method causes an increase in peripheral resistance, the normal level of blood pressure in the animal is maintained by a reduction in its cardiac output. The reduction in cardiac output is usually attained through a decrease in heart rate (bradycardia).

Bradycardia and selective vasoconstriction are methods of oxygen conservation commonly exhibited by diving vertebrates like alligators, birds, seals, and whales. Though humans exhibit a diving reflex, this reflex does not contribute to the long term survival of persons submerged in cold water. Submersion hypothermia consists of the person drowning in cold water which cools his core simultaneously with the cold water he is submerged in cooling his skin. Young, skinny individuals survive being drowned in cold water for up to an hour due to the rapid drop in core temp.

The dive reflex generally does not last any more than 2-3 minutes and therefore plays a minor role in the survival of young people drowned in cold water. Adults do not survive for any long period of time drowned in cold water.

The history behind the explanation of the dive reflex saving drowned children is due to Dr. Martin Niemeroff who pioneered saving drowned students. Unfortunately, his explanation on why these individuals survived was not supported by any research.In this experiment, students will determine their normal heart rates while resting, holding their breath, and holding their breath as they submerge their faces in cool water.

Experiment Set-up

Equipment Required

  • PC or Mac Computer
  • IX-TA data acquisition unit
  • USB cable
  • IX-TA power supply
  • PT-104 Pulse plethysmograph
  • Three pans, each with 3” of water at 5, 15, or 25°C
  • iWire-B3G (optional)
  • RM-204 Respiration monitor (optional)

IX-TA Setup

1. Place the IX-TA on the bench, close to the computer.
2. Check Figure T-1-1 in the Tutorial Chapter for the location of the USB port and the power socket on the IX-TA.
3. Check Figure T-1-2 in the Tutorial Chapter for a picture of the IX-TA power supply.
4. Use the USB cable to connect the computer to the USB port on the rear panel of the IX-TA.
5. Plug the power supply for the IX-TA into the electrical outlet. Insert the plug on the end of the power supply cable into the labeled socket on the rear of the IX-TA. Use the power switch to turn on the unit.

Start the Software

1. Click on the LabScribe shortcut on the computer’s desktop to open the program. If a shortcut is not available, click on the Windows Start menu, move the cursor to All Programs and then to the listing for iWorx. Select LabScribe from the iWorx submenu. The LabScribe Main window will appear as the program opens.
2. On the Main window, pull down the Settings menu and select Load Group.
3. Locate the folder that contains the settings group, IPLMv6Complete.iwxgrp. Select this group and click Open.
4. Pull down the Settings menu again. Select the DivingReflex settings file from Human Heart.
5. After a short time, LabScribe will appear on the computer screen as configured by the DivingReflex settings.
6. For your information, the settings used to configure the LabScribe software and the IX-TA unit for this experiment are programmed on the Preferences Dialog window which can be viewed by selecting Preferences from the Edit menu on the LabScribe Main window.

7. Once the settings file has been loaded, click the Experiment button on the toolbar to open any of the following documents:

  • Appendix
  • Background
  • Labs
  • Setup (opens automatically)

Pulse Transducer Setup

HH-5-S1

Figure HH-5-S1: The PT-104 pulse plethysmograph.

1. Locate the PT-104 pulse plethysmograph (Figure HH-5-S1) in the iWorx
2. Plug the DIN8 connector to the PT-104 (plethysmograph) into the Channel A5 input of the IX-TA (Figure HH-5-S2).
3. Place the plethysmograph on the volar surface (where the fingerprints are located) of the distal segment of the left middle finger or thumb, and wrap the Velcro strap around the end of the finger to attach the unit firmly in place.
4. Instruct the subject to sit quietly.

Optional Experiment

Use the iWire-B3G cable to record an ECG as well as the pulse and heart rate.

HH-5-S2

Figure HH-5-S2: The PT-104 connected to the IX-TA.

Experiment

Exercise 1: Heart Rate at Rest
Aim: To measure the heart rate of a subject at rest.

Procedure

1. Click on the Record button, located on the upper right side of the LabScribe Main window.

Note: If the user clicks the Record button and there is no communication between the iWorx unit and computer, an error window will appear in the center of the Main window. Make sure the iWorx unit is turned on and connected to the USB port of the computer. Click OK and select the Find Hardware function from the LabScribe Tools menu.

2. Click on the AutoScale button at the upper margin of the Pulse and Heart Rate channels. Your recording should look like Figure HH-5-L1.

    • If the signal on the Pulse channel is upside down when compared to trace in Figure HH-5-L1, click on the downward arrow to the left of the channel title and select the Invert function. The trace should now look similar to the one in the figure.
    • If the pulse signal is small or noisy, adjust the tension on the strap holding the pulse plethysmograph to the finger.

3. When you have a suitable trace, type <Subject’s Name> Resting Heart Rate in the Mark box to the right of the Mark button. Press the Enter key on the keyboard to attach the comment to the data. Record for a minute.
4. Click Stop to halt recording.
5. Select Save As in the File menu, type a name for the file. Choose a destination on the computer in which to save the file, like your lab group folder. Designate the file type as *.iwxdata. Click on the Save button to save the data file.

HH-5-L1

Figure HH-5-L1:The pulse and heart rate recording of a subject at rest displayed in the Main Window

Data Analysis
1. Scroll through the recording and find a twenty second section of data with exemplary pulse waves. Since the subject is breathing normally, the trace on the Heart Rate Channel should cycle, which demonstrates normal respiratory sinus arrhythmia.
2. Use the Display Time icons to adjust the Display Time of the Main window to show at least two complete heart rate cycles on the Main window. Two complete heart rate cycles can also be selected by:

    • Placing the cursors on either side of a group of two complete heart rate cycles;
    • Clicking the Zoom between Cursors button on the LabScribe toolbar to expand the segment with the two complete heart rate cycles to the width of the Main window.

3. Click on the Analysis window icon in the toolbar (Figure HH-5-L2) or select Analysis from the Windows menu to transfer the data displayed in the Main window to the Analysis window (Figure HH-5-L3).

LabScribe Toolbar

Figure HH-5-L2:The LabScribe Toolbar.

4. Look at the Function Table that is above the uppermost channel displayed in the Analysis window. The names of the mathematical functions used in the analysis, Max, Min, and Mean, appear in this table. The values for these three parameters on each channel are seen in the table across the top margin of each channel.

Pulse Heart Rate Recording

Figure HH-5-L3:The pulse and heart recording of a subject at rest displayed in the Analysis window.

5. Once the cursors are placed in the correct positions for determining the maximum, minimum, and mean heart rates in the section of data displayed in the Analysis window, the values of these parameters can be recorded in the on-line notebook of LabScribe by typing their names and values directly into the Journal, or on a separate data table.
6. The functions in the channel pull-down menus of the Analysis window can also be used to enter the names and values of the parameters from the recording to the Journal. To use these functions:

    • Place a cursor on the left margin of the data displayed in the Analysis window, and the other cursor on the right margin of the displayed data.
    • Transfer the names of the mathematical functions used to determine the maximum, minimum, and mean heart rates to the Journal using the Add Title to Journal function in the Heart Rate Channel pull-down menu.
    • Transfer the values for the maximum, minimum, and mean heart rates to the Journal using the Add Ch. Data to Journal function in the Heart Rate Channel pull-down menu.

7. Enter the subject’s resting heart rate into Table HH-5-L1.

Exercise 2: Heart Rate and Apnea
Aim: To measure the heart rate of a subject while they are holding their breath.

Procedure
1. Remind the same subject to sit quietly with their hands in their lap. Instruct the subject to hold his or her breath as long as possible in this exercise.
2. Click on the Record button. The signal should begin scrolling across the screen.
3. Click on the AutoScale button at the upper margin of the Pulse and Heart Rate channels. Your recording should look like Figure HH-5-L1. Use the same techniques used in Exercise 1 to display the signals properly.
4. When the pulse recording is a suitable trace, type Holding Breath in the Mark box to the right of the Mark button. Press the Enter key on the keyboard to attach the comment to the data as the subject begins to hold his or her breath (apnea).
5. Quickly type Breathing Again in the Mark box to the right of the Mark button. Press the Enter key on the keyboard to attach the comment to the data when the subject resumes breathing. Continue recording for thirty seconds after the subject begins breathing again.
6. Click Stop to halt recording.
7. Select Save in the File menu.

Data Analysis
1. Scroll through the recording and find the section of data that was collected while the subject was holding his or her breath.
2. Use the Display Time icons, or the cursors and the Zoom between Cursors button, to adjust the Display Time of the Main window to show the data from ten seconds before the subject held his or her breath to twenty seconds after breathing resumed.
3. Click on the Analysis window icon in the toolbar to transfer the data displayed in the Main window to the Analysis window (Figure HH-5-L4).
4. Place one cursor at the point when the subject held his or her breath and the other cursor at the point breathing resumed.
5. Look at the Function Table in the Analysis window and make sure the mathematical functions used in the analysis, Max, Min, and Mean, appear.
6. Use one of the techniques explained in Exercise 1 to record the values for these parameters in the Journal, or on a separate data table.
7. Enter the subject’s heart rate during apnea into Table HH-5-L1.

Heart rate change during apnea

Figure HH-5-L4: Heart rate change during apnea.

Questions

1. How does the subject’s average heart rate while resting compare to the heart rate while holding breath?
2. How do the subject’s maximum and minimum heart rates while resting compare to the same heart rates while holding breath?

Exercise 3: Heart Rate While Testing the Diving Reflex

Aim: To measure the effects of “diving” into cold water on heart rate.

Procedure
1. Have the subject sit in front of a pan of room temperature water (25oC). If the subject wears glasses, the glasses should be removed. If the subject has long hair, the hair should be pulled back away from the face.
2. Click on the Record button. The signal should begin scrolling across the screen.
3. Click on the AutoScale button at the upper margin of the Pulse and Heart Rate channels. Use the same techniques used in Exercise 1 to display the signals properly.
4. When the pulse recording is a suitable trace, type 25oC Water in the Mark box to the right of the Mark button.
5. Instruct the subject to hold his or her breath and submerge his or her face (up to the hairline and in front of the ears) in water for 20 seconds. Press the Enter key on the keyboard to attach the comment to the data as the subject’s face enters the water.
6. Quickly type Face Out of Water in the Mark box. As the subject pulls his or her face out of the water, press the Enter key on the keyboard.
7. Click Stop to halt recording after this trial.
8. Select Save in the File menu.
9. Repeat the diving exercise into the pan of 25oC water two additional times. Allow enough time between trials for the subject’s heart rate to return to normal.

Note: If a preliminary examination of the data indicates the subject’s heart rate did not change, the subject may not have a good diving reflex. Select another subject to perform this exercise.

10. Repeat this exercise with the same subject submerging his or her face in pans of water at 15°C and 5o°C.

 Data Analysis

1. Scroll through the recording and find the first trial when the subject submerged his or her face in 25°C water.
2. Use the Display Time icons, or the cursors and the Zoom between Cursors button, to adjust the Display Time of the Main window to show the data from ten seconds before the subject submerged his or her face to twenty seconds after removing his or her face from the water.
3. Click on the Analysis window icon in the toolbar to transfer the data displayed in the Main window to the Analysis window.
4. Place one cursor at the point when the subject submerged his or her face in the water and the other cursor at a point five seconds later.
5. Look at the Function Table in the Analysis window and make sure the mathematical functions used in the analysis, Max, Min, and Mean, appear.
6. Use one of the techniques explained in Exercise 1 to record the values for these parameters in the Journal, or on a separate data table.
7. Move one cursor to the point that is five seconds before the subject removed his or her face from the water and the second cursor to the point when the subject’s face was removed from the water. Record the maximum, minimum, and mean heart rates for this time period as performed in Step 6.
8. Repeat these measurements for each of the three trials at 25oC, 15oC, and 5oC.
9. Determine the averages of the maximum, minimum, and mean heart rates in the first five seconds and the last five seconds of submersion at each temperature. Enter these values on Table HH-5-L1.

Table HH-5-L1:Heart Rate at Rest, during Apnea and Facial Exposure to Different Temperatures.

Heart rate at rest

Questions
1. What happens to the subject’s heart rate as their face is submerged in water at 25oC?
2. What happens to the subject’s heart rate as their face is submerged in water at 15oC? In water at 5°C?
3. What causes the subject’s heart rate to change when their face is submerged in cold water?
4. How does the mammalian diving reflex help a person who falls into cold water? Think in terms of the organs that need oxygen.

Appendix: Measuring Respiration Rate and Depth
Attaching a RM-204 respiration monitor to the subject permits relative changes in the subject’s rate and depth of respiration to be measured during normal breathing, apnea, and testing the diving reflex. The use of a respiration monitor is optional and it is not required to complete the exercises in this experiment.

1. Locate the RM-204 respiration monitor (Figure HH-5-L5).
2. Plug the DIN8 connector of the RM-204 respiration monitor into the Channel 4 input of the iX-214 (Figure HH-5-L6); or the Channel A6 input of the IX-TA (Figure HH-5-L7).
3. Wrap the elastic belt of the respiration monitor around the subject’s chest at a level that is below the sternum. Place the sensor inside the belt so that the sensor is in the center of chest at a level that is even with the subject’s elbows.
4. If the subjects are sitting during these exercises, they should sit erect so that the muscles involved in pulmonary ventilation are able to move with few restrictions.

Respiration Monitor

Figure HH-5-L5: The RM-204 respiration monitor

Respiration monitor connected to the IX-214 recorder

Figure HH-5-L6: The RM-204 connected to the IX-214.

Respiration connected to the IX-TA control module

Figure HH-5-L7: The RM-204 connected to the IXTA.

Pulse wave, respiration, heart rate and breathing rate recording

Figure HH-5-L8: The pulse wave, respiration, heart rate, and breathing rate recorded with a PT-104 pulse plethysmograph and a RM-204 respiration monitor.

Note: An interesting addition to the analysis of this lab is to look at the change in amplitude of the pulse, often seen even if little rate change is seen. The very reliable reduction in amplitude is a good measure of reduction of blood flow to the fingers, as seen in peripheral vasoconstriction.