Exploring the Diving Reflex

In our practical we set out to test the diving reflex for ourselves. To explore this phenomenon, we conducted an experiment to test how heart rate varies in different conditions, both in and out of the water.

In Experiment 24/25, conducted this year with 36 students, we measured heart rates in several different conditions: The five primary measures are depicted in the chart below (head above water, holding breath above water, holding breath underwater, snorkel above water and snorkel underwater). Additionally, we took sub measurements every 10 seconds that the participant held their breath underwater. In Figure 3 the full range of conditions is depicted, where each line represents the data of one student.

• When the head was above water, the average heart rate was about 82bpm. Holding the breath above water reduced the heart rate to an average of 75bpm, indicating an initial physiological response to apnoea.

• Holding the breath underwater resulted in the lowest heart rate of 65bpm, showcasing the classical diving reflex. At this point, with the face submerged in water, the parasympathetic nervous system is triggered, slowing the heart rate to conserve oxygen for vital organs.

• Interestingly, snorkeling above water increased the heart rate to an average of 80bpm, possibly also due to the effort involved in maintaining steady breathing through the snorkel.

• Finally, snorkeling under water led to a drop in heart rate to 76 bpm in average,

As the charts below show, it worked! To undermine our results, it is further interesting to compare the data from the 36 students this year (figure 2) to the 25 students that did the same practical last year (figure 1)! In figure 3 we see some individual differences in the reflex. Some people are more nervous than others at the beginning of an experiment. This is completely normal and there is no right or wrong in this. 

Figure 1 (experiment 23/24)

Figure 2 (experiment 24/25)

Figure 3 

On the x-axis you see the different condition of the experiment. On the y-axis you can see the heart rate.