The Guinness world record for underwater breathing record (for a human), which was done by breathing 100% O2 for 30 minutes before the dive, resulted in a breath-holding record of 20 min and 21 sec. What problem does 100% O2 solve?
What is different here from humans “free diving” (with records of 11 min and 35 sec)? Or a sea turtle submerged for 10 hrs. and 14 min?
Please help, thank you.
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It does two things, but first you need to take a moment and think about how gases behave in a liquid under pressure.
First, all gases will dissolve in water as a function of the partial pressure of that gas and the amount of time spent under that pressure. The atmosphere is about 79% nitrogen, 21% oxygen, and a few trace gases in there to round it out. That nitrogen and oxygen dissolves in the plasma of the blood. Oxygen is principally carried by the hemoglobin in the red blood cell, but it is also found as a dissolved gas. Nitrogen is only found dissolved in plasma. If the atmospheric pressure increases, more of the gases will dissolve in the plasma. When the pressure decreases, the gas will bubble out of solution (boil).
By breathing 100% oxygen for 30 minutes prior to diving, the diver washes nitrogen out of the blood. The nitrogen isn't used metabolically and since there is no nitrogen in 100% oxygen, it diffuses out of the blood into the alveoli and is exhaled. The longer you breathe 100% O2, the more nitrogen you will wash out. When you dive to a significant depth, you are under much greater atmospheric pressure (33ft = one additional atm of pressure). When you surface, those dissolved gases will bubble out of solution. That's why normal divers have to ascend slowly -- so the gases equilibrate slowly and don't bubble out all at once. If they ascend too quickly, the nitrogen forms bubbles which block blood vessels and cause the bends (which can be fatal). If you breathe oxygen first and don't have much nitrogen, if any, in your blood then you can ascend as rapidly as you need to -- which is good if you've been holding your breath for 20 minutes.
Second, your oxygen carrying capacity is maintained at very near your maximum all the time. If the hemoglobin is fully saturated, the only way to get more oxygen into the blood is to dissolve more in the plasma. By breathing 100% oxygen you replace the nitrogen with oxygen which can be used metabolically while you're holding your breath so you can stay down longer. Not by much, but enough to make a difference.
Free divers hyperventilate as much as possible first, then descend. This drives down the amount of CO2 dissolved in the blood. CO2 is what drives you to breathe so lowering that as much as possible gives you more time before needing to surface. Free divers have to be careful on ascent. They don't spend as much time at depth but they are still prone to the bends. That's why you'll see them exhaling all the way up as they ascend to get rid of as much waste gas as possible as it comes out of solution as the pressure decreases.
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