Investigating the simulated diving reflex in professional divers

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