Master of Science
Shoemaker, J Kevin
Background: Submergence underwater activates the diving response (DR) in both diving mammals and humans in order to preserve oxygen. Some evidence suggests that the DR can be trained in humans to provide a larger magnitude of bradycardia during submergence.
Hypothesis: Individuals with breath holding experience will have a greater magnitude of bradycardia during the DR than untrained, age-matched controls.
Methods: Participants performed three different protocols: 1) an apnea to volitional end point, or until 30 seconds of involuntary breathing movements were observed (APNEA), 2) one minute of cold pack to the forehead (COLD), and 3) one minute of cold pack contact on forehead during an apnea (COLD+APNEA).
Results: BHD had a larger magnitude of bradycardia during COLD+APNEA compared to controls (p=0.099).
Conclusions: The greater magnitude of bradycardia and MAP response in BHD shows that there is a physiological difference between trained and untrained individuals in breath hold diving.
Summary for Lay Audience
When mammals dive underwater the activate a reflex that allows them to maintain as much oxygen in their blood as possible. This reflex is called the diving response (DR). The characteristics of the DR are a reduction in heart rate (HR), an increase in blood pressure, and an increase in the blood vessels throughout the body constricting. In order to measure how extreme the DR is you measure how much HR decreases. Some researchers have found that some individuals can actually train the DR to be more extreme by practicing diving and breath holding.
This study investigated whether or not the DR can actually be trained by observing whether professional breath hold divers had a more extreme response than naïve individuals.
Professional breath hold divers (BHD) and naïve individuals who have never completed breath hold training participated in this study. They completed three different trials: 1) all participants held their breath for as long as possible; 2) an ice pack was placed on their forehead; 3) they held their breath for as long as possible while an ice pack was placed on their forehead.
This study found that BHD recovered their HR faster than naïve individuals. This means that their HR recovered to normal resting levels at a faster rate than naïve individuals after just a cold pack was placed on their forehead.
These results indicate that the BHD have developed some adaptation in recovery to cold exposure. Otherwise, there were no adaptations observed that related directly to the extremity of the DR.
Smith, Sydney O., "Investigating the simulated diving reflex in professional divers" (2019). Electronic Thesis and Dissertation Repository. 6799.