Name. Lab Partners. The Dive Response. In this lab exercise, you will be designing and conducting your own experiments!

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1 Name Lab Partners The Dive Response In this lab exercise, you will be designing and conducting your own experiments! Note: A formal report is due for this lab (see handout). Objectives 1. Characterize aspects of the dive response in humans during a simulated dive. 2. Identify factors that trigger the dive response. Background The dive response is characterized by three major physiological responses: (1) apnea, (2) bradycardia, and (3) peripheral vasoconstriction. Apnea, or breath hold, is a natural response for any air-breathing mammal or bird that is submerged. Bradycardia, or reduced heart rate, is associated with a reduction in metabolism in order to conserve oxygen. The slowing of the heart rate also helps to match perfusion with diffusion. Because the animal is not breathing diffusion has slowed. Consequently, perfusion of the pulmonary vessels also slows. Peripheral vasoconstriction is another oxygen-conserving response. Blood is directed away from nonessential organs and from tissues such as skeletal muscle, which have their own oxygen stores in the form of myoglobin. The overall response increases the availability of blood (and thus oxygen) to the brain and heart, while simultaneously decreasing oxygen consumption by the heart. The dive response is one of several adaptations that enable some marine mammals to remain submerged for over an hour. The dive response is particularly well developed in marine mammals, but it is also manifested in humans. In this exercise you will monitor heart rate and peripheral perfusion to characterize the response to a simulated dive (submerging the face in cold water). You will also design your own experiments to investigate the factors that trigger the dive response.

2 Equipment You will be using two pieces of equipment to examine the physiological responses associated with diving. A Polar heart rate monitor is commonly used in exercise physiology, to monitor the heart rate of athletes on the move. The transmitter belt contains two electrodes to detect the electrical activity of the heart. The belt sends the information to a receiving watch, which translates the signal into a heart rate. The heart rate will appear as a digital readout on the watch. Check your heart rate monitor by pressing the electrodes against the skin, just beneath the pectoral muscles. A little heart-shaped symbol should begin flashing on the watch. If you do not see the flashing symbol, try pressing the large plastic button on the watch. If you still have trouble, ask your TA for assistance. The second piece of equipment you will be using is an infrared thermal sensor. This sensor detects the black body radiation of the object or animal at which it is aimed. Black body radiation is heat energy radiating off a surface, in the form of electromagnetic radiation (light). Humans emit black body radiation in the infrared part of the electromagnetic spectrum. The infrared thermal sensor detects this light; because the wavelength of the light is inversely proportional to the heat energy, the sensor can convert the light reading into a temperature. You will be using the sensor to detect skin temperature, as a proxy for perfusion. The more blood that flows to a region near the surface of the body, the more heat radiated from that area. Therefore, skin temperature should be warmer in regions that are well perfused with blood, while skin temperature should be cooler if blood flow is reduced. When you depress the trigger, the infrared temperature sensor will provide a digital readout of the temperature in Celsius. Make sure you record the readout on the viewing screen that reads to the tenth of a degree. You may need to share infrared sensors among all lab groups, so you will need to stagger your experimental periods with the other groups experiments. SAFETY WARNING: The infrared sensor has a laser guide to help you make measurements from precise locations on the body. NEVER point the laser into anyone s eyes. Preparing the Subject 1. Place the Polar heart rate monitor on the subject. In order for the electrodes to make better contact, it helps to wet the electrodes before placing them on the skin. The heart rate monitor should fit snugly on the front of the chest, just beneath the pectoral muscles. 2. Check the placement of the monitor by looking for the flashing heart signal on the receiver watch. Make sure you can get a heart rate reading on the watch before proceeding. 3. If the subject has long hair, he/she should tie it back. 4. Position the subject in front of the dishpan so he/she can comfortably submerge his/her face for 30 seconds. The subject s hand should be on the lab bench with the palm facing

3 up, to facilitate skin temperature measurements. 5. The subject should remain as calm as possible. Boisterous subjects have been reported to show very poor diving responses! Part 1. Demonstrating the Dive Response 1. Fill a dishpan with cold water (~15 C). Water surface temperature can be measured with the infrared thermometer pointed at the water. Record this number. 2. Control period: The subject should be seated with his/her face out of the water and breathing normally. a. Record the subject s resting heart rate. Have one group member write down the heart rates displayed on the receiver watch for 30 seconds of rest. b. Record skin temperature at a peripheral location: the palm of the hand. c. Record skin temperature at a core location (e.g., the belly or back). 3. Simulated dive: The subject should take a deep breath, submerge his/her face in the water to the level of the temples, and remain in that position for 30 seconds. a. Record the subject s diving heart rate. Have one group member write down the heart rate(s) displayed on the receiver watch throughout the 30 seconds. b. Record skin temperature at the peripheral location. c. Record skin temperature at the core location. 4. Look at the data to ensure that you obtained the expected response. If you didn t see a dive response (especially lowered heart rate during the dive), try again with a different subject. Different people show the dive response to different degrees. Remember- the quieter the subject, the greater the potential response. Yoga mediation helps! Part 2. Identifying Factors that Trigger the Dive Response In this part of the exercise, you and your group will conduct your own experiments to investigate the factors that trigger the dive response in humans. For your experiments, you will focus on bradycardia as the principle dive response. You may investigate the effects of body position, water temperature, breath hold, exercise, etc. A good starting point is to test the response with the subject holding their breath in air versus with their face in water. This is your time to be creative! Have fun! You should conduct three or more experiments to test different triggers. 1. Before you begin the experiment, make some predictions. a. What factor(s) do you think will trigger the dive response in humans? b. Which factor do you think is most important for triggering dive response?

4 2. Each experiment should include a 30-second control recording and a 30-second recording of the experimental condition. 3. You should test a single factor each time. In other words, only one thing should differ between the control and the experimental condition, or you will not be able to interpret your data. Therefore, the control conditions you use will differ among experiments, and will differ from the one used in the first part of the lab. Be sure to ask your TA if you have questions about whether your control is appropriate. 4. When you think you ve identified a trigger, repeat the experiment, ideally with more than one subject. It is better to do a thorough job identifying one trigger than to test as many factors as you can. Data Recording You will be recording heart rate over 30-second periods. If the watch reports more than one heart rate over that period, record the different heart rates and report the average. You may also want to compare the lowest heart rate recorded during experimental trials. (This can be considered the maximum dive response of the individual.) You will only record one skin temperature at each site per trial. Make sure you record skin temperature to the tenth of a degree. Carefully record the conditions you created for each control and experimental trial. Below are examples of tables to help you organize your data. You may need to modify these tables for your own data recording, depending on your experiment. PART 1. Demonstrating the Dive Response Heart Rate Peripheral Core DIVE Heart Rate DIVE Peripheral DIVE Core

5 PART 2. Identifying Factors that Trigger the Dive Response EXPERIMENT 1 EXPERIMENT 2

6 EXPERIMENT 3 EXPERIMENT 4 (optional)