I'm not sure about those figures. I'm not a trauma person but have made some observations and can do some math here. Let's start with 3 liters of blood in an average adult:
http://en.wikipedia.org/wiki/Blood
The cardiac ouput of a typical adult is about 5 liters at rest, but let's assume we're not completely zen about our knife attack and say it's ten, because that's also how many fingers I have:
http://en.wikipedia.org/wiki/Cardiac_output
Of this, about 15% goes to the brain, so we're talking 1.5 L per minute:
http://en.wikipedia.org/wiki/Cerebral_blood_flow
Now let's assume that the carotid artery in question carries about 40% of the blood flow in question. It's not 50% because we have vertebral arteries in our spine that do some of the work, and because when arteries are injured, they spasm.
Thus, the blood output of a carotid artery at stress = 2x resting blood flow is 0.6 L per min.
According to Wiki once again, a serious hemorrhage resulting in changes in mental status (class III) occurs with the loss of 30-40% of blood volume:
http://en.wikipedia.org/wiki/Bleeding
Out of our 3 liters that means 1.2 L (let's use the 40% since we are talking about tough, conditioned uechi-ka).
That means you've got about two minutes of single-carotid squirting before your mentation is gone (0.6L/min x 2 minutes = 1.2 L, 40% of 3L). Do I 100% believe this calculation? Naw. But I trust it more than the 5 seconds to unconsciousness listed for a carotid cut.
How could you possibly lose enough blood in 5 seconds to become unconscious? You can completely CEASE blood flow to the head (say, rear naked choke) and last 5 seconds, and there's no way to reduce the cardiac output that quickly by losing volume, because the heart would be pumping blood returning in the veins and wouldn't even be able to perceive a drop in the return of blood for a while longer. The first thing it would notice would be the absence of the blood return from one carotid. Since the brain gets about 15% of cardiac output, the carotid represents at most 7.5% of blood flow, so for at least a while your heart will just work a bit harder, which it does whenever we exercise or wait for American Idol results or whatever. After that, the body can clamp down on the veins, mobilizing mostly stagnant blood for circulation. Then it cuts off flow to the skin, and many internal organs (brain, heart and kidneys last) sending reserve to essential areas. As blood return declines, cardiac output declines too--not good for your brain, but it slows further losses.
This is why:
I've met a guy who had a carotid artery knife transection repaired at UVA med center (later killed by a bullet, proving the aphorism "trauma is a chronic disease with acute exacerbations").
I met a guy in a VA prison who slit his brachial artery in jail and had to conceal what he was doing on consecutive 10 minute suicide checks until he finally passed out.
That soldier in "Black Hawk Down" whose femoral artery was shot managed to get dragged to a building and proceduralized by the medic (without avail) before drifting away from hypotension.
I met a jehovah's witness who had both his arms torn off by a fence post drilling axle that caught his clothes--not only didn't die, he survived without a blood transfusion.
There was discussion that the french medics who saw Diana killed her by not getting her to the hospital and instead trying to resuscitate at the scene--her pulmonary artery was torn, and she was bleeding into her chest. The pulmonary artery receives ALL (the main trunk) or HALF (either branch, right or left to the lungs) of the right cardiac output (equal to the systemic, left cardiac output except in strange situations).
I've read about a man who survived a stab wound to his left ventricle. He thought he'd been punched, but managed to stagger inside his own house before collapsing and was resuscitated with some brain damage.
If you think about it, there's no reason for someone to have "immediate unconsciousness" from a heart stab, since you have a few seconds of blood to work with even if the heart fibrillates completely. Instead, what happens is that the blood spills into the chest (minor) and more importantly into the inflexible sack around the heart, preventing the heart from filling and thus from emptying (cardiac tamponade). Depending on the hole and whether it forms a one way valve or a two way valve, blood might move into the pericardium slowly, or back n forth, slowing the effect on filling, just as a collapsed lung can have a one way hole (results in rapid filling of the chest with air, squishing the lungs, heart, and kinking off the vessels).
I will say that bleeding can be impressive. I had the unique experience of watching someone bleed from their subclavian. I havd been sent to pull a line from a 19 year old's vein (he was seriously brain injured and not reporting symptoms). When I did so, all seemed normal, and I was holding pressure when I noticed his heart rate climb up, to double, and his blood pressure fall, and his skin turn white. This happened over about 3-4 minutes, with him on ICU monitoring equipment the whole time. I called a code blue, and it was probably 15 minutes before anything was done for the kid besides a little IV fluid. What was done was a chest XRay showing new fluid on the line side of the chest (no suprise) and this was followed with a chest tube to drain it. In retrospect, the filling of his right chest with blood probably ceased the bleeding and removing what had collected was potentially dangerous. Anyhoo, kid got through all of this without clinical consequences from his experince, although he was shortly thereafter made comfort care and died. The line was either in his artery, not his vein, or was holding back a nick in the artery, albeit one smaller than a knife induced severing.
Long story short, if someone cuts your radial or brachial artery, keep fighting. You need to remove the threat and you're not gonna die in 5 seconds. I recommend not letting knives into your carotids (which at least you can compress), hearts, or subclavians (can't even compress those).
