Can the heart pump without a brain to begin with? If the heart stops first, is the heart more sensitive to oxygen loss?
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The heart stops first. Think of the heart as a motor, and the brain as a power supply. The motor provides energy to the power supply. Neural tissue can store energy for a short time after its “motor” stops. This is why if someone who has gone into cardiac arrest, if they’re revived soon enough they will be able to avoid brain injury/death.
Emergency services often learn about the “tripple two”. 2 weeks without food, 2 days without water and 2 minutes without air.
And the last one is what you are wondering about. The heart is a muscle. And like all muscles, its controlled by your brain. In particular, its a basic system controlled by the stem of your brain. Just like breathing.
So when the brain dies. Your heart stops. And your brain dies after running out of oxygen. Roughly 2 minutes after your last breath.
When you take a heart from a body that is functioning well, the heart will keep beating for a while more. This is called muscle memory. Its a queue of signals from your brain that was not yet completed, but stored locally.
If you are interested in having a heart working without a brain, you can. The signal it needs is a low voltage and ampere power pulse. This is how they keep hearts healthy between organ donors.
You have two questions here. If you stop breathing, oxygen can’t get in and you’ll get a build up of CO2 in the blood and it can’t get out. The CO2 buildup reacts with water to form an acid…so your blood starts becoming acidic as well as hypoxic (low oxygen).
Cells will start to die off in a couple of minutes, however the heart will still beat trying to remove the CO2 and deliver more oxygen. You will get permanent damage to all cells within 2-4 minutes and probable irreversible brain death within 6. Meanwhile the heart is trying to do whatever it can while it itself is going hypoxic. So it starts doing flipflops as those heart cells become affected.
Whichever one dies first will be difficult to determine unless you have an EEG to measure brain activity while also looking at an ECG for the heart. My money is on the heart doing at least one beat here and there before the brain kicks. And you have to have a solid definition of death while you’re at it.
Your second question is in regards to whether the heart can beat without a the brain. Most definitely because the heart cells possess something mysterious called automaticity which allows them to beat in absence of anything else. You can take out a heart, place it on a tray and as long as it is washed in electrolytes it will beat for quite some time. [If you chill it, it can last 4 hours or so.](https://insh.world/science/your-heart-can-continue-beating-outside-your-body/#:~:text=With%20the%20help%20of%20some,it%20starts%20beating%20like%20normal.). Mind you, if you chill the brain, it can recover after a while once its warmed back up.
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