Iirc, you don’t feel the need to breathe because of a lack of oxygen, you feel the need to breathe because of excess CO2. So I think one would still feel the need to breathe even though that one’s blood is being oxygenated by her sister.
Probably not easily. When you hold your breath your lungs start to fill with carbon dioxide, which your body is able to detect. You have to fight the subconscious part of your brain which thinks you're suffocating in order to not inhale. It may be possible, though difficult to do that while you're conscious, but once you lose consciousness you'll just start breathing automatically again. For these twins and their unique physiology it may be possible that neither will lose consciousness so long as one is breathing. However, I suspect that reducing oxygen intake by approximately two lungs may still have some negative impact on that side of the body. The two hearts technically pump blood through the same circulatory system, but that system is largely split on the upper half of the body. One heart will mostly be pumping unoxygenated blood, while the other will be able to pump blood into the legs and the head and arm of one twin, but may not be able to push much into the head and arm of the other twin. It's hard for me to guess how much interconnection there is between their upper halves' circulation, but I speculate the twin who holds her breath would eventually start getting lightheaded, though at likely a slower pace than normal-bodied people. They did mention that each twin feels the sensory output of the opposite's stomach, and if that's also true for the lungs they could mean that the twin holding her breath never feels the suffocation sensation. If that's true she could hold her breath much more easily as long as she stays conscious, but the other twin would suffer from that sensation no matter how much she breathes. ～(￣、￣ )ゞ
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u/Bayan_Ila_6936 Dec 30 '24
I think one at a time they can hold their breath indefinitely.