Wednesday, March 30, 2005

life, brain function, death and in between- a brief guide

The cells in the body require energy not only to function, but to stay alive. If they do not have a source of energy(oxygen and other stuff) they first stop working, and then die. It is like the ice cream in your freezer. If you shut off the electricity for a short time, it will soften, but will still be ice cream if you get the electricity back on in time. If you wait too long, it will be melted goo, and even if you freeze it again, it will never be ice cream again.

The oxygen comes by breathing air through the lungs, and it gets pumped around by the heart. So, the cells can die if either the breathing stops, or the heart stops. The electrical system of the heart is kind of on automatic. It will pump as long as there is a supply of oxygen. It doesn't need any outside signals to tell it to pump. You can take a frog heart out(a common experiment in biology classes) and watch it keep on beating. It is pretty much self triggering. The lungs are different. There is an area in the brain(brainstem to be exact) where the signal to breath starts. It gets sent down the spinal cord, then to nerves(phrenic) that go to the diaphram, that moves up and down. If the signal is interrupted anywhere along that path, from brainstem to diaphram, then there is no breathing. Therefore, breathing can stop becuase of brain injury, or spinal cord injury(think Christopher Reeve). And, unless the person is put on a respirator(breathing machine) death will follow pretty quickly.

Consciousness is a bit more complicated. There is an area in the brainstem called the reticular activating system that is kind of an on/off switch for consciousness. If you damage it enough, you will be unconscious. You can also lose consciousness from extensive damage to both sides of the front part of the brain(cerebrum- the part that makes our foreheads stick out and distinguishes us from apes).

Brain death is a situation where the brain has been totally and irreversably damaged. There are criteria(known as the Harvard criteria, for the place where they were first promulgated) for brain death. Unfortunately, not eveyone always goes by the criteria, the criteria themselves are vague in places, and actually the definition is different in other countries. There is a bottom line however: there can be absolutely no brain function, no breathing, no brain reflexes(a bunch of things your face does that you have no conscious control over, like your pupils getting smaller in light, etc), studies that show overwhelming brain damage(like a CT or MRI), no blood flow to the brain (you inject dye into the arteries and take pictures that show that the blood doesn't enter the arteries of the brain). You can have spinal reflexes(there is a cool one that is rarely seen, called the reflex of Ivan, where all the muscles contract at once, makes it look like the person is sitting up, but it is just a reflex). Measuring brain waves(EEG) doesn't help a whole lot, although if one is done it needs to be flat(no activity). Then you have to repeat the exam at least 12 hours later to make sure that there is no brain function, especially no breathing(have to disconnect the ventillator and watch the patient for a while to see if they breath or not).

(For those interested, the skull can be thought of as a box, filled with the brain, blood vessels, etc. When the brain is injured, it swells, taking up more space. IF there is a blood clot, or a tumor, that also takes up space. As the volume of brain, swelling, blood clot, etc increases, the pressure in the skull increases, because the skull does not expand. If the process is bad enough, the pressure in the skull gets very high. Remember blood pressure? that is the force that the heart is exerting to push the blood around the body. If the pressure in the skull gets to be equal(or higher) than the blood pressure, then no blood gets into the skull(or the brain). This makes more brain die, and adds to the swelling, which increases the pressure, and it is this cascade of events that lets one establish that a person is truly brain dead- the pressure in the skull is too high for blood to get in, and the brain cannot last for much longer than 5 minutes without blood supply.)

What happens with a brain injury? this can be from car accidents, gunshot wounds, episodes where the heart stops or the blood pressure drops and no blood gets to the brain for a while(called a stroke), bleeding in the brain(also called a stroke, sometimes hemorrhagic stroke) and other reasons. Sometimes a lot of brain is injured, sometimes just a little. Sometimes the pictures(CT or MRI scans) show a lot of damage, sometimes they dont. Sometimes parts of the brain are only temporarily not working, and take a while to get better. Sometimes there is permanent damage. Many times it is hard to tell how much better a person will get. Frequently with severe brain damage, the patient isn't breathing enough, and needs to be on a breathing machine. Over time, unless there is severe damage(or brain death), most start to breath on their own. Most patients who are going to get better will start to do so in the first few weeks. Most improvment happens in the first 6 months. It is very rare to have significant improvement past 1-2 years after the injury. The scans of the brain also will change with time, but after a week or two will usually show the extent of the injury, and unless there is an additional problem, will not change significantly after 6 months.

Coma, or persistant vegetative state(pvs) is a description of someone who does not respond to their surroundings. It is a description of the patient, therefore established by observation and examination, not by scans, EEG's or anything else. Obviously, the CT and MRI scans can show why, and define the anatomic extent of the brain damage, but you can have people in pvs with not a whole lot wrong on their scans(maybe damage in the on/off reticular activating system), or people with almost no brain left whatsoever, but enough that their breathing centers are telling the diaphram to move.

What is concsiousness? How do we measure it? These are tough questions. Usually we consider consciousness to be evidence of non-reflex behavior, or, a little more stringent, purposeful behavior. Moving a hand away in response to pain(or more accurately, a stimulus, because feeling pain implies that one is conscioius enough to have a response to a stimulus that we recognize as pain) does not imply consciousness, it can be a reflex. Slapping the hand that is pinching the person implies consciousness. As you can see, there is a significant grey area where a person could be considered conscious or not, depending on the interpretation of the movements and responses. We have a not of reflexes- movements that are not dependent on thinking, that happen automatically, and these sometimes are confused with purposeful behavior as well.

In view of recent events and discussions, I hope this has been helpful. The amount of ignorance, especially on the part of some of our elected officials has been astounding. To quote R. Gil, this has been only for purposes of education , not l'halacha. for specific problems, please consult a competent authority.

Comments-[ comments.]


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