How much blood does a person have, and how does it vary for body weight?
What percentage of blood can one loose without dying?
What are the effects of blood loss? I have heard that you loose color vision with extreme blood loss.
How long does it take to recuperate from moderate to extreme blood loss? What is that recuperation like?
I have a bit of first hand experience with a large amount of blood loss. I’ll spare the details, but no, it wasn’t self-inflicted.
The average human body contains 6 quarts.cite
I lost 4 pints of blood, and was still alive. It felt like I was dead though. I did receive a pint through transfusion. FYI, I was 14 years old, and weighed 127 lbs.
I’m not too sure about the loss of colour vision, but everything did fade. The easiest way to describe it is it actually feels like your life-force is slowly ebbing away. That is the only way I can describe it. You do feel weak, woozy, like you are falling, there is no stability to anything.
I was in bed for roughly 4 days, eating a lot of food, and just resting, as the body needs to replenish the supply of blood. As well, you need to worry about things such as the lowered amount of oxygen in the system. 2 things you do not want to do are do drugs (including cigarettes), and drink. Caffeine is also out of the picture.
Hope that sheds some light on the subject for you.
About the loss of color vision thing:
The retina requires a relatively high amount of oxygen to work properly. In a low oxygen environment, it is entirely possible that the retina would not receive enough oxygen to work properly and reduced or missing color vision could, in theory, be one of the symptoms.
More commonly, though, “tunnel vision” is experienced, with the outer edges of vision fading, then the effect moving inward towards the center of vision. This gives an effect much like looking down a tunnel, hence the name.
I have no idea how much blood you’d have to lose to get to this point, however.
This sounds contradictory to how the cones and rods are placed in the eye, and opposite of most vision loss cases that I have seen. If you lose the function of the cones(loss of color), then you wouldnt you also lose the high definition and center vision? Can you explain how one can lose the function of color and still have center vision?
Depends on how deeply you want this “explained”. I can’t give you the physiological underpinnings of the phenomena, no, however –
Being a pilot there are two conditions I can get into that result in a lack of oxygen going to the eyeballs. One, I can get so high that there isn’t sufficient oxygen in what I’m breathing, i.e. “hypoxia”. “Tunnel vision” is listed as a symptom of hypoxia much more frequently than “loss of color vision”.
The other situation involves excessive g-forces, which literally pull the blood out of your head into your lower body. Again, “tunnel vision” is listed as a symptom. So is “grey-out”, a fading of vision to grey or even black (if you fall unconcious). Grey-out usually also involves tunnel vision effects.
Perhaps there is some mechanism that funnels blood and oxygen to the sharper, center vision in preference to the periphery as a survival mechanism. I don’t know. I do, however, feel a reluctance to argue with the data compiled by the Air Force, Navy, and NASA in regards to this.
I’m actually not sure if tunnel vision is a retina or brain thing. It can be explained both ways. The density of photoreceptors in the center of vision (the macula) is highest. So, if hypoxia causes a non-specific loss of photoreceptors, you will lose the periphery of your vision before you lose the center of your vision (because of the density). If cones require more oxygen, then you would see a lack of color vision with a decrease in visual acuity in the center of vision. But I think Broomstick’s explanation of greying out is more accurate – that is a central brain thing when you are losing consciousness.
It can also be explained due to the blood supply to the striate cortex. Blood flow is highest to the center of the cortex, which corresponds to the macula. Therefore, in hypoxia, the neurons becoming ischemic first are the ones on the periphery, farthest away from the blood source. If I were placing bets, though, I’d go with the retina thing.
Well, it’s also hard to deprieve just the retina of oxygen and blood without affecting anything else in the head - like the brain. And the optic nerve. Both of which are also highly metabolically active bits of tissue.
And then there’s the question of how healthy tissue reacts versus diseased tissue.
It’s possible you get several visual effects at once - typically, those experiencing these phenomena are not in a position to take detailed notes, and there aren’t a lot of volunteers for undergoing massive blood loss voluntarially.
Last summer I experienced a couple of fainting spells where I lost colour vision (greyed out as mentioned above). It was not due to blood loss, but restricted blood circulation ( I think anyhow) but its much of a muchness in this case.