How long can a human live without its head?

Answer 1

If a clean guillotine decapitation occurs, a few factors come into play. First, the blood vessels all vasoconstrict -- they'll close down, trapping oxygenated blood in the head. Also, neurological functions will start to shut off, reducing oxygen usage, in order to deal with the increasing hypoxia (this is also observed in drownings). As such, you can expect the head to "live" in various conditions for as much as a few minutes. You can expect consciousness for as much as 30 seconds and possibly more. Anectodotal reports of Guillotine (the doctor; not the device) come to us of experiments with convicted criminals who would answer YES with one eyeblink and NO with two blinks. The story goes that Guillotine ran out of questions before they stopped responding (over 2 minutes). Personally, I doubt this, but I don't know. On the other side of the equation is systemic shock. An injury like this would slam the patient into a (eventually terminal) shock. That, coupled with the hypoxia, indicates a super-fast loss of upper brain functions. So what one describes as "life" comes into question. As to the body, death would occur quickly, but would do so an organ at a time. Organ death depends a lot on which organ and how it's treated. You are no doubt aware that organs can be donated for quite some time post mortem.

Answer 2

10 seconds.

Answer 3

1 second