The Mammalian Dive Response
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Abstract
The presence of a dive response in humans when the face is submerged in water was studied. A lot of mammals have shown to exhibit a dive response known as the mammalian dive reflex. During this reflex bradycardia, a slowing of the heart rate, is shown. In this study, human subjects were put through various tests to determine if humans also exhibit bradycardia. Subjects heart rates were measured while breathing normally, while holding breath and while holding breath with face submerged in water. The results showed that there was a significant decrease in heart rate while submerged in water as compared to normal breathing or holding breath out of water. Many other studies have been done that agree with the results found in this study. However, this study would have had more significant results had other factors of the dive reflex been tested for.
Introduction
Mammals have shown to have a special reflex that allows them to dive to deep depths for long periods of time without coming up for air. This is known as mammalian dive reflex or MDR. This reflex has also been studied to see if it applies to humans. Professional breath-hold diving has been a common practice in several countries for many centuries, for harvesting sponges, pearls and seafood (Ferretti and Costa 2002). This practice is declining; however, in Japan and Korea there are still around 30,000 divers. Many studies have looked at the physiological aspects of these divers. Studies of diving operations and patterns, seasonal variations, diving equipment, gas compositions at the end of dives, and estimated gas exchange during diving have been done in order to better understand what the factors are effecting these dives (Ferretti and Costa 2002).
When looking at these studies, respiratory and cardiovascular changes were found. These would show a link to diving mammals and humans. One thing found to happen as a dive response was bradycardia. Bradycardia is a slowing of the heart rate (Sterba and Lundgren 1985). This slowing of the heart rate allows the oxygen in the blood to be conserved over a longer period of time. Harbor seals freely diving at sea are able to depress their heart rate to around 4 beats per minute (Hochachka 1999). In one study, a volunteer consistently displayed profound bradycardia at around 6 bpm (Hochachka 1999). This goes to show that a dive response in humans is possible. Many studies look at adaptations in oxygen storage, pressure, ventilation and locomotion (Steele 2001). The study done in this paper is focusing on bradycardia and the hypothesis that humans exhibit this slowing of the heart rate. It is important to collect more information on this subject to better understand whether or not humans could adapt to diving for long periods of time. The findings from this experiment are going to show that humans do exhibit a dive response.
Methodology
This lab was conducted on August 29, 2003. This lab was set up in order to determine if humans do exhibit a dive response. To create a “norm”, pulse rate was taken of each student while breathing normally. The pulse was taken by counting the number of heartbeats per 10 seconds and multiplying this number by six in order to get a full minute. These numbers were then recorded. To determine if water was the cause of pulse change, pulse rate was recorded while holding the breath outside of the water. As the third treatment pulse rate was recorded while faces were submerged underwater. This pulse rate was taken after 5 seconds of submersion so that the initial heart rate due to anxiety of submersion was not a factor. The pulse rates that were recorded (Figure 4) were used in t-Tests in order to determine the p-values of the different treatments. A significant p-value is one that is below 0.05. Descriptive Statistics were also done in order to determine the mean, median, standard deviation, skew, and kurtosis. All this information was used to determine whether or not there was a significant change in the pulse rate that would indeed show a dive response in humans.
Results
The results of the first t-Test between the holding breath treatment and the submerged treatment (Figure 1) showed a p-value of 1.03E-04. This was said to be significant. The second t-Test between the normal treatment and the submerged treatment (Figure 1) showed a p-value of 7.60E-06, which was also said to be significant. There were no other combinations of t-Test p-values that were significant. When looking at both p-values it was obvious that there was a greater difference in pulse rate between just holding ones breath and actually being submerged. This would lead to the belief that some type of diving response was shown. All the descriptive statistics that were done are shown in Figure 2. This was basically used to get the standard deviation of the results. All the statistical analysis was summarized in a chart (Figure 3) that shows the great decrease in heart rate while submerged as compared to the other treatments.
Discussion
This study was designed to determine if humans could show a diving response induced by breath holding and facial submersion. The results from this study match a lot of other studies that have been conducted. This study showed a significant decrease in pulse rate with facial submersion. Kawakami et al. found in their study of the effects of face immersion breath-hold showed that there was a decrease of