Feb 23, 2016 07:15 AM
(This post was last modified: Feb 23, 2016 01:30 PM by elte.)
http://www.hawaiireporter.com/heads-up-t...illing-you "The effect of gravity on brain circulation is purely mechanical, and relates to the position of the head relative to the pumping heart. When we are standing up, the head is above the heart, so blood must pump against the force of gravity — from the heart to the brain — lowering the effective pressure with which the arterial blood is delivered to the brain. Meanwhile, drainage of blood from the brain to the heart is facilitated by the pull of gravity.
In contrast, when we lie down and are horizontal, the heart and head are now on the same plane. This eliminates the effects of gravity on brain circulation. Blood from the heart pumps powerfully into the head without gravity’s resistance, increasing intracranial pressure. And blood returning from the brain to the heart must do so without gravity’s assistance, causing a back-up of blood in the brain.
Essentially, intracranial pressure increases, and overall brain circulation diminishes, when you are lying flat compared to standing up.
Of course, the body is intelligent and has mechanisms for controlling brain pressure under different gravity situations. When the brain gets pressurized from lying down, there are various pressure receptors in the head and neck designed to lower blood pressure, thereby preventing too much brain pressure and the possibility of blowing a blood vessel or creating a cerebral aneurysm. This is why blood pressure is lower when we are sleeping, and horizontal.
But these brain mechanisms for adjusting pressure have their limits. As we go through the day in a vertical position, gravity relentlessly pulls our body’s fluids downwards, which is why many people have swollen feet and ankles by day’s end. Once we lie down, the gravity effect is lost, as fluid leaves the legs and returns to the head. So despite our brains normal defense mechanisms, throughout the night intracranial pressure increases and is highest in the morning, after hours of lying flat, and lowest at the end of the day, after hours of being vertical.
What happens when intracranial pressure is high from long periods of lying flat? The increased arterial pressure causes extra cerebral spinal fluid to form in the brain’s ventricles, increasing intracranial fluid pressure. The ventricles swell and the cells of the brain become bathed in excess fluid, essentially causing brain edema. This edema would lower the available oxygen and sugar for brain cells. The lack of gravity assisted drainage from the brain would cause a back-up of blood in the venous system and collecting sinuses in the brain. The brain’s circulation would become relatively stagnant, as the only force moving blood through would be the pushing force of the arterial pressure (which is greatly reduced after going through the cerebral circulation) and the sucking force of the heart’s right atrium. And in addition to the brain swelling under the pressure, the eyes, ears, face, sinuses, gums — the entire head — will become pressurized and the tissues congested with fluid!
There is one field of medicine that avidly studies this effect of gravity on physiology. That sub-specialty is Space Medicine. Astronauts in space are in a zero-gravity field, and it is known that this causes blood to shift to the head and brain, causing increased brain pressure and accompanying migraines, glaucoma, Meniere’s disease, and other problems associated with a pressurized, congested brain. To study the negative effects of zero-gravity here on Earth, these space scientists have people lie down flat! However, since medicine is so wide a field, with sub-specialists learning more and more about less and less, there is little exchange of ideas between space medicine and Earth-bound medicine. Otherwise, someone would have realized that lying flat is what we do when we sleep. If it causes problems for astronauts, then couldn’t it cause problems for everyone else?
We found out about this Space research while we performed our own research into sleep positions as a possible cause of migraines. We hypothesized that sleeping too flat for too long each night could lead to brain pressure and fluid accumulation (edema) within the brain tissue, with associated hypoxia and hypoglycemia. The brain cannot function well without proper amounts of oxygen or sugar, and this condition would be at its worst in the morning, which is when most migraines occur."
"...too long each night could lead to brain pressure and fluid accumulation (edema) within the brain tissue..." That in particular matches my personal observation.
In contrast, when we lie down and are horizontal, the heart and head are now on the same plane. This eliminates the effects of gravity on brain circulation. Blood from the heart pumps powerfully into the head without gravity’s resistance, increasing intracranial pressure. And blood returning from the brain to the heart must do so without gravity’s assistance, causing a back-up of blood in the brain.
Essentially, intracranial pressure increases, and overall brain circulation diminishes, when you are lying flat compared to standing up.
Of course, the body is intelligent and has mechanisms for controlling brain pressure under different gravity situations. When the brain gets pressurized from lying down, there are various pressure receptors in the head and neck designed to lower blood pressure, thereby preventing too much brain pressure and the possibility of blowing a blood vessel or creating a cerebral aneurysm. This is why blood pressure is lower when we are sleeping, and horizontal.
But these brain mechanisms for adjusting pressure have their limits. As we go through the day in a vertical position, gravity relentlessly pulls our body’s fluids downwards, which is why many people have swollen feet and ankles by day’s end. Once we lie down, the gravity effect is lost, as fluid leaves the legs and returns to the head. So despite our brains normal defense mechanisms, throughout the night intracranial pressure increases and is highest in the morning, after hours of lying flat, and lowest at the end of the day, after hours of being vertical.
What happens when intracranial pressure is high from long periods of lying flat? The increased arterial pressure causes extra cerebral spinal fluid to form in the brain’s ventricles, increasing intracranial fluid pressure. The ventricles swell and the cells of the brain become bathed in excess fluid, essentially causing brain edema. This edema would lower the available oxygen and sugar for brain cells. The lack of gravity assisted drainage from the brain would cause a back-up of blood in the venous system and collecting sinuses in the brain. The brain’s circulation would become relatively stagnant, as the only force moving blood through would be the pushing force of the arterial pressure (which is greatly reduced after going through the cerebral circulation) and the sucking force of the heart’s right atrium. And in addition to the brain swelling under the pressure, the eyes, ears, face, sinuses, gums — the entire head — will become pressurized and the tissues congested with fluid!
There is one field of medicine that avidly studies this effect of gravity on physiology. That sub-specialty is Space Medicine. Astronauts in space are in a zero-gravity field, and it is known that this causes blood to shift to the head and brain, causing increased brain pressure and accompanying migraines, glaucoma, Meniere’s disease, and other problems associated with a pressurized, congested brain. To study the negative effects of zero-gravity here on Earth, these space scientists have people lie down flat! However, since medicine is so wide a field, with sub-specialists learning more and more about less and less, there is little exchange of ideas between space medicine and Earth-bound medicine. Otherwise, someone would have realized that lying flat is what we do when we sleep. If it causes problems for astronauts, then couldn’t it cause problems for everyone else?
We found out about this Space research while we performed our own research into sleep positions as a possible cause of migraines. We hypothesized that sleeping too flat for too long each night could lead to brain pressure and fluid accumulation (edema) within the brain tissue, with associated hypoxia and hypoglycemia. The brain cannot function well without proper amounts of oxygen or sugar, and this condition would be at its worst in the morning, which is when most migraines occur."
"...too long each night could lead to brain pressure and fluid accumulation (edema) within the brain tissue..." That in particular matches my personal observation.