Why the study?
What are the relative contributions of voluntary apnoea, face immersion in water, and cold exposure to diving bradycardia in normal subjects?
What are the relative contributions of voluntary apnoea, face immersion in water, and cold exposure to diving bradycardia in normal subjects?
Voluntary apnoea and cold exposure are the primary drivers of diving bradycardia, with face immersion in water providing a synergistic effect when combined.
Findings in healthy subjects should not yet change practice; hypothesis-generating for mechanisms of bradycardia in cold-water immersion.
Diving or face immersion bradycardia is a well recognized but incompletely understood reflux which occurs in man and other mammals. 2. In order to investigate the contributions made by voluntary apnoea, face immersion in water and cold exposure, 18 normal subjects were exposed to these challenges separately and in various combination. 3. Tested individually, cold and apnoea caused significant reductions in heart beat (P < 0.01 and 0.002, respectively). Face immersion in thermoneutral water had no effect on heart rate. 4. The bradycardic effect of apnoea at maximal inspiration may be due to stimulation of pulmonary stretch receptors. 5. Cold exposure and voluntary apnoea applied simultaneously caused a summative effect but when tested with face immersion in water there was a synergistic response greater than the sum of individual responses. 6. The results confirm the bradycardic effect of apnoea and cold exposure, whereas immersion in thermoneutral water had little effect, a finding which has been disputed in the literature.
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Marsh et al. (1995) studied this question.
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