Analysis of the Mammalian Dive Response

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Texas A&M University *

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Biology

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Apr 3, 2024

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Analysis of the Mammalian Dive Response Emma Dawson Bio 112-515 November 9, 2023 Abstract The following report explores the mammalian dive response through a series of experiments and tabulated data. The introduction will explain the reflexes during the dive response phenomenon and a prediction for the outcome of the experiments. The protocol and any deviations from the steps will be highlighted in the methods section of this report. Any tables, graphs, and figures are included in the results along with a brief analysis of the trends taking place. The hypothesis will be refuted or supported in the discussion of conclusions based on the experimental results. Introduction The phenomenon explored using experiments is a set of reflexes known as the dive response found in mammals. The dive response includes a combination of bradycardia, apnea, and peripheral vasoconstriction. Bradycardia is the slowing of the heart, apnea is breath- holding, and peripheral vasoconstriction decreases blood flow by constricting peripheral blood vessels. The primary function of this response is to conserve oxygen to increase the time before damage to the brain or heart happens (Foster, 2005). During the simulation to capture the human reflexes, apnea, cooling, and water immersion will be used, and the effects those variables have on heart rate will be monitored. The expectation for this experiment is that the test subject will experience bradycardia when submerged in water and holding their breath. It is also expected that the colder the temperature of the water is, the slower the heart rate will go. Methods This experiment utilized six groups containing one test subject in each to make the data as consistent as possible. The test subject has one team member counting their pulse, another 1

timing the dives or breaths, and one writing down results. The first activity is done by each of the six groups, but only 2 groups are needed for each activity 2, 3, and 4. For the first lab activity, a tub was filled approximately halfway with water. The water needed to reach roughly 15  C, so handfuls of ice were added until that temperature was attained. The first part of this activity was air breathing. The test subject was instructed to stand bent over with their face hovering over the water and breathing normally. The beats per minute were measured for two sets of 15 seconds. The two intervals were averaged together to achieve the full 30-second average heart rate. The second part of the activity was apnea in cold water, where the subject was instructed to hold their breath and dip their face under the cold water. The heart rate was measured the same as air breathing in two 15-second intervals and taking the average. The results of this activity and the average heart rate decrease can be seen in Table 1 and Figure 1. In lab activity 2, the effects of apnea are tested in and out of the cold water with two test subjects. The subject stands bent over with their face above the water breathing for two 15-second intervals, while someone took their heart rate. Those two heart rates are averaged for the thirty-second column. The same system is used again but the test subject held their breath above the water. The average decrease in heart rate is taken for those two parts. The test subject is then instructed to use a snorkel during the cold dive to breathe underwater instead of holding their breath. Heart rates are taken for that, and then the subject repeats the dive but must hold their breath. Table 2 displays the results for all four trials and the average heart rate decreases. The effects of facial immersion are simulated in lab activity 3. The two test subjects used a snorkel to breathe in the air and the heart rate was measured. This data was compared to the average heart rate trials for the same test subjects using the snorkel while diving under cold water. Once the average heart rate decrease was taken, the test subjects were given a 15- minute break. Now the test subjects were instructed to hold their breath above the water and hold their breath under water to measure and compare the data with apnea. Once again, the test subjects are given a 15-minute break to rest before repeating the second set of trials for 2

apnea in water, but the water used for facial immersion is room temperature instead of ice cold. Lab activity 4 focused on the effects that temperature has on the heart rate of a mammal. The test subject was instructed to hold a room temperature gel pack to their forehead above the water and breathe. Once the average heart rates were taken for that trial, the same thing is done with a cold pack now instead of a room temperature one. The same test subject is then instructed to immerse their face in warm water that is approximately 22  C for two 15-second time intervals. Those measurements for heart rate are taken while the subject rests in preparation for the cold dive. The same test subject now repeats the same steps as before in the cold tub, which is about 15  C. The average decrease was taken and put into Table 4 and Figure 4. Results For the results and discussions sections of the paper, only lab activities 1 and 4 will be talked about in depth. The tables for activities 2 and 3 will still be included along with an explanation of the trends. In a simulated dive, the two conditions being tested were air-breathing and apnea in cold water. The average heart rate was measured for 0-15 seconds, 15-30 seconds, and the average of those were taken for 0-30 seconds. The class averages for air-breathing were stable, which makes finding a trend easier. Unfortunately, the class averages for apnea in cold water were more erratic. However, the average heart rate decrease between the two trials was still negative. This means that the heart rate did decrease after “diving” into the cold water. Table 1: Lab Activity 1 – Simulated Dive Condition Group Avg. HR 0-15 s Avg HR 15-30 s Avg HR 0-30 s Air Breathing 1 100 84 92 2 88 92 90 3 96 96 96 4 84 88 86 5 64 80 72 6 83 83 83 Class Average 85.833 87.167 86.5 3

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