As a scuba diver, I’ve been fascinated by the freedom offered by freediving. However, ditching all that scuba gear is associated with greater risk of decompression sickness and lung-overexpansion when freediving to great depths. Freedivers that go beyond five meters without the use of any breathing or buoyancy control gear, use many of the same techniques as other diving air-breathing animals to maximize their potential elapsed dive time and depth on a single breath. Experienced freedivers become bradycardic and peripheral blood vessels vasodilate quickly after beginning decent. There have also been observed increases in EPO to increase red blood cell count and speed of chemoreceptor response to low O2, such that repeated training causes chemoreceptors to take up more oxygen per breath over time. The amount of total body oxygen circulating after just one breath and the ability to cope with incredibly high ambient pressures at depth are the key physiological limits to how long and how deep a person can freedive.
One key to becoming an elite freediver is practicing in a way that hones physiological processes that maximize blood oxygen and delivery, just as habitually diving air breathers do. This study evaluated how the world’s best freedivers might be different physiologically. Surprisingly, freedivers simultaneously activate the sympathetic and parasympathetic neural controls of the body to vasoconstrict and slow heart rate, respectively. Some heart rates have even been recorded as low as 14 beats a minute in competitive divers. The adrenal glands are also activated during a dive to secrete catecholamines that start the body’s fight or flight response. Interestingly, there has been some reported adrenal control of the spleen to increase blood volume, and therefore the transportable oxygen in the body.
The physiology that prevents lung suppression or collapse as divers approach records around 1,000 feet is not only critical to their survival, but fascinating. It turns out that vasoconstriction reroutes blood to surround the lungs and the chest shrinks to balance pressure between the lungs and the water. In extreme cases, the diaphragm and other organs can shift up into the chest cavity to help match the ambient water pressure around the lungs. While this may sound incredibly detrimental, analysis of sympathetic nervous system chemicals like acetylcholine and ACTH return to homeostatic levels and the organs return to their usual places after a dive, indicating there is little long term damage associated with these physiological changes.
https://www.youtube.com/watch?v=IDbmG5KFnqc
References
Bonphoto Bonaire (Producer). (2011, June 2). Freediving on Bonaire, Dutch Caribbean [Video file]. Retrieved October 12, 2017, from https://www.youtube.com/watch?v=8i0_hmb6P5g
Ostrowski, A., Strzała, M., Stanula, A., Juszkiewicz, M., Pilch, W., & Maszczyk, A. (2012). The Role of Training in the Development of Adaptive Mechanisms in Freedivers. Journal of Human Kinetics, 32, 197–210. http://doi.org/10.2478/v10078-012-0036-2
The exhilarating peace of freediving [Video file]. (2015, December 10). Retrieved October 12, 2017, from https://www.youtube.com/watch?v=IDbmG5KFnqc
Worrall, S. (2014, August 10). Free Diving World Record Will Soon Be Pushed to 1,000 Feet, Author Says. National Geographic. Retrieved October 12, 2017, from http://news.nationalgeographic.com/news/2014/08/140810-free-diving-sperm-whales-jules-verne-reunion-booktalk/
This was a very interesting blog. Thank you for posting it Josie. I am also a scuba diver and have always been fascinated with free diving. I think that it is amazing that free divers have found a way to "control" their involuntary functions. There has be some research that links the ability to hold your breath with physical fitness. That being said, I can't even hold my breath through Eisenhower Tunnel.
ReplyDeletehttp://steveedwardsfitness.com/holding-breath-fitter/
Well, if you're a diver that's probably for the best! After, the cardinal rule is 'don't hold your breath!'
DeleteI've lived in CO all my life and I've noticed I use significantly less air than most other divers (almost as much BT as nitrox divers). I've often wondered if this has been a result of my body being physiologically adapted to the high altitude/low oxygen environment around here. Have you lived in CO long and experienced anything similar? Or am I finally just making the final metamorphosis to being a mermaid?