Hypoxia & Underwater Breath Holding

SW

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This is a great-read BBC article that's worth finding a few minutes to get through. Some particularly interesting points I found:

-How this guy survives is amazing.
-How your spleen plays a role in breath holds
-How temperature can dramatically increase breath hold lengths
-Why you see 'the light at the end of the tunnel' effect when about to black out


-SW
 

Yukon

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The diver's survival was both lucky and amazing. His metabolic state was such he no longer had self control or self determination in influencing his survival. The diver was also no longer holding his breath, but for the oxygen saturated in the blood within the spleen to contribute to his survival there must be some sort of heart generated circulation happening.

Therapeutic hypothermia is a medical treatment technique of lowering body temperature to decrease metabolism which puts the patient in a state of unconscious torpor. There is a fine torpor demarcation of not making the patient so unconscious that they die.

https://www.smithsonianmag.com/science-nature/can-humans-ever-harness-power-hibernation-180961835/Can Humans Ever Harness the Power of Hibernation?

Human hybernation
 

Yukon

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An interesting historical perspective, reference study of Aerobic exercise before diving reduces venous gas bubble formation in humans in the article. Gives appearance research into influences of physical activities immediately before and after a dive is a recent interest.

Back in either 1978 or 1979 the Air Force School of Aerospace Medicine, then at Brooks AFB, conducted a research study into this. The concern was to establish what were the risks to PJs flying on an aircraft immediately after conducting a dive operation. Several PJs volunteered to be the test subjects.

There were several factors driving this study. One of which is most dive operations conducted by Pararescue were significantly away from recompression chambers and there were a few recovery operations conducted inland at high elevation requiring the getting there and back on helicopters. There were no published decompression tables or other guidance for diving at altitude and it was primarily PJ doing in-land away from the sea coast recovery diving operations for aerospace equipment and materiel and human remains recovery back then whereas the Navy called such activities Salvage Operations.

The U.S. Navy Diving Manual didn't address diving at elevations above sea level until about 1980. Below is cut-and-paste from U.S. Navy Diving Manual, revision 7, 30 April 2018.

Because of the reduced atmospheric pressure, dives conducted at altitude require more decompression than identical dives conducted at sea level. The air decompression tables, therefore, cannot be used as written. Some organizations calculate specific decompression tables for use at each altitude. An alternative approach is to correct the altitude dive to obtain the equivalent sea level dive, then determine the decompression requirement using standard tables. This procedure is commonly known as the “Cross Correction” technique and always yields a sea level dive that is deeper than the actual dive at altitude. A deeper sea level equivalent dive provides the extra decompression needed to offset effects of diving at altitude.

9-13.2 Need for Correction. No correction is required for dives conducted at altitudes between sea level and 300 feet. The additional risk associated with these dives is minimal. At altitudes between 300 and 1000 feet, correction is required for dives deeper than 145 fsw (actual depth). At altitudes above 1000 feet, correction is required for all dives.

9-13.3 Depth Measurement at Altitude. The preferred method for measuring depth at altitude is a mechanical or electronic gauge that can be re-zeroed at the dive site. Once re-zeroed, no further correction of the reading is required.
 
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