Mechanism of the Bradycardia of the Diving Syndrome as Seen in Divers Using Scuba in Water of 55, 45, and 35 Degrees F.
NAVY CLOTHING AND TEXTILE RESEARCH UNIT NATICK MASS
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Physiologists monitored heart rates of test subjects using SCUBA gear under water. Comparisons were made between heart rates immediately before and after subjects entered the water, and at 5-minute intervals while they were immersed in water. Data showed a difference in percent of decrease when initial heart rates were 90 and above or less than 90. However, data showed the decrease to be maximal within 5 minutes of submersion within a return towards presubmersion levels after 30 minutes. It is believed that initial heart rate changes were brought about immediately by a reflex vagal response to immersion. Increased venous return due to water pressure is the apparent cause of the longer term effect. A physiological adaptation to the pressure allowed return towards control values by the end of the 30-minute period. Author
- Stress Physiology