Analysis of the Mammalian Dive Response

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 Cold Water 1 88 68 78 2 123 62 92.5 3 80 68 74 4 40 40 80 5 96 72 84 6 57 61 59 Class Average 80.667 61.833 77.917 Average HR Decrease -5.166 -25.934 -8.583 1 2 3 0 10 20 30 40 50 60 70 80 90 100 85.83 87.17 86.5 80.17 61.83 77.92 Lab Activity 1 - Simulated Dive Air Breathing Apnea in Cold Water 0-15s 15-30s 0-30s Avg HR Figure 1: Lab Activity 1 – Simulated Dive Bar Chart In lab activity two, the effects of apnea, test subjects compared their breathing in the same conditions as holding their breath. The average heart rate decreases for air-breathing compared to apnea and snorkel diving compared to apnea while diving is both around zero. This means that the effects are not very drastic, and the average decrease in the heart rate was little to none. Table 2: Lab Activity 2 – Effects of Apnea Condition Group Avg. HR 0-15 s Avg HR 15-30 s Avg HR 0-30 s Air Breathing 1 96 80 88 2 93 91 92 4

Exp Average 94.5 85.5 90 Apnea in Air 1 92 72 82 2 100 94 97 Exp Average 96 83 90 Average HR Decrease +1.5 -2.5 0 Snorkel Cold Dive 1 92 80 86 2 80 83 81.5 Exp Average 86 81.5 83.175 Snorkel Cold Dive (apnea) 1 80 76 78 2 98 78 88 Exp Average 89 77 83 Average HR Decrease +3 -4.5 -.175 Lab activity 3 was done to measure the effects of facial immersion. Facial immersion does cause an average decrease in heart rate regardless of the temperature or if breathing is being done. This is shown in the lab activity 3 table where the average heart rate decrease is negative for every trial. Table 3: Lab Activity 3 – Effects of Facial Immersion Condition Group Avg. HR 0-15 s Avg HR 15-30 s Avg HR 0-30 s Snorkel Breathing in Air 1 80 76 78 2 80 80 80 Exp Average 80 78 79 Snorkel Cold Dive 1 76 64 70 2 - - - Exp Average 76 64 70 Average HR Decrease -4 -14 -9 Apnea in Air 1 84 72 78 2 76 76 76 Exp Average 80 74 77 Apnea in Cold Water (enter simulated dive data here) 1 76 64 70 2 72 64 68 Exp Average 74 64 69 Average HR Decrease -6 -10 -8 Apnea in Air (from above) 1 88 80 84 2 70 70 70 5

1 2 3 4 0 20 40 60 80 100 120 Lab Activity 4 - Effects of Temperature Avg HR 0-15s Avg HR 15-30s Avg HR 0-30s RT gel pack Cold gel pack Apnea warm water Apnea cold water Avg HR Figure 4: Lab Activity 4 – Effects of Temperature Bar Chart Discussion Lab activity one was able to show that during the simulated dive, a human experiences bradycardia or a slower heart rate. Evidence for this is the average decrease being in the negative numbers for all six test subjects. This decrease in heart rate could also be evidence of peripheral vasoconstriction since the water used for the simulated dive was cold. Cold water could be the reason for peripheral vasoconstriction because the response is triggered to regulate body temperature by redirecting blood flow to the center of the body where the vital organs are ( Kiyatkin, 2021). This does support the hypothesis that apnea, while submerged in cold water, does decrease the average heart rate in mammals with no discrepancies in the data. However, lab activity four had more surprising and contrasting data. In exploring the effects of temperature on the dive response, average heart rates showed to increase for every temperature. The average resting heart rate for the test subject was taken initially as 72 bpm, and it was expected that the heart rate would slow in colder temperatures and increase in warmer temperatures. For the first two trials breathing with two different gel pack 7

temperatures, the average heart rate increases for cold and stays steady at room temperature. When heart rate increases, this is known as tachycardia. It has been shown in other studies that there is an increase of 10 beats per minute per degree centigrade (Davies, 2009). This does not support the hypothesis that a temperature decrease causes a decrease in the average heart rate. Furthermore, the second set of trials for apnea in warm and cold water also refutes this hypothesis. The average heart rate showed to increase more in cold water than in warm water. There may have been errors while conducting this experiment that led to contrasting results. This could have been caused by outside factors that were not tested on the test subject. There could have been something that was bothering the test subject in a way that could cause an increase in heart rate when it did not before. This is not very surprising since the test subject is asked many times to immerse their face in water and to hold their breath. This can be stressful for mammals since they need oxygen to survive. Literature Cited 1. Davies P, Maconochie I. The relationship between body temperature, heart rate, and respiratory rate in children. Emerg Med J. 2009 Sep;26(9):641-3. 2. Foster, G. E., & Sheel, A. W. 2005. The human diving response, its function, and its control. Scandinavian Journal of Medicine & Science in Sports, 15(1), 3-12. 3. Kiyatkin EA. Functional role of peripheral vasoconstriction: not only thermoregulation but much more. J Integr Neurosci. 2021 Sep 30;20(3):755-764. 8