You are absolutely correct. My statement above that the brain is all liquid is just plain wrong. I think I got confused by reading about this from Wikipedia.
"Brain tissue in its natural state is too soft to work with, but it can be hardened by immersion in alcohol or other fixatives, and then sliced apart for examination of the interior."
After a brief review of some very gross pictures on the internet of brain crashes, it is clear that the brain is liquid fluid and blood and spongy brain material. Sorry I was so wrong...Now, to some of your very interesting questions.
1eye wrote:What is the "normal" CSF pressure? How is it regulated?
Dr. Flanagan in his book "The Downside of Upright Posture" writes that
"Blood pressure in your arm is about 120 mmHg over 80 mmHg. That means that when the heart contracts, blood pressure rises to about 120 mmHg. In between beats, when the heart contracts, blood pressure rises to about 120 mmHg. In between beats, when the heart relaxes, it drops down to about 80 mmHg. That's fairly low, relatively speaking. While it takes a tight tourniquet to stop a bleeding artery, it only takes light finger pressure to compress a vein and stop blood flow. At about 10 to 20 mmHg, CSF and intraocular pressures are extremely low."
1eye wrote: Is there a good non-invasive way to measure instantaneous pressure? Seems to me ultrasound might accomplish this, if pressure affects the propagation of the sound waves. Would have to be a very sensitive and well calibrated instrument.
This is where Dr. Flanagan, again in the same book as some very interesting things to say. I am not done with the book, but he makes a strong point in arguing that glaucoma, may share the same disease process as NPH but it is with the eye, not the inner brain. His discussion that the eye is just an extension of the brain's third ventricle is fascinating. With this parallel in mind he goes on to write.
"Chronic glaucoma was once a major cause of degeneration of the optic nerve and subsequent blindness. It was difficult to detect and there were no treatments. Physicians had to rely on primitive spring gauges, called tonometers, which were pressed against the eyeball to check pressure. The spring gauges weren't that sensitive or accurate. Nowadays, fortunately, early detection has reduced the incidence of blindness due to glaucoma dramatically. Rather than spring gauges, today's eye doctors use computerized contact applanation and non-contact or air puff tonometry, as well as other highly sophisticated means, which are much more sensitive and accurate at detecting the extremely low pressures of glaucoma. When the condition is detected, drugs are now available that can decrease intraocular pressure and prevent blindness"
Perhaps some of these methods could be used to measure brain pressure? Or perhaps he discusses this later in his book, which I will post as I get there.