Every one of us has a mysterious double life.
For about two thirds of the time we are conscious beings, thinking about the world within and without, and negotiating our ways through the obstacles of life. For the other one third of the time we are nearly lifeless lumps of flesh, unconscious to everything but our own fantasies, as we lie flat in bed asleep. We all know that sleep is important for health. But for an activity that consumes about 8 hours of everyday of life, surprisingly little is thought about the act of sleeping, or the way our culture teaches us to sleep. Sleep behavior, like all human activities, is defined by our culture.
Sometimes, the practices taught by our culture can impact on the way our bodies function. As medical anthropologists, we research ways our cultural practices may be affecting our health. And we have found that the way we have been trained to sleep may be one of the most important causes of various diseases plaguing our society.
Of course, when you consider the culture of sleeping, it includes such isues as the length of time to sleep, and time of day for sleep. Do you take frequent naps or do you sleep 8 hours straight? Do you sleep at night or during the day?
Other issues concern sleepwear. Do you sleep nude, or with pajamas or lingerie? Do you sleep in your underwear? Should the sheets be natural fabrics, such as cotton or silk, or is polyester okay? What about the detergent and fabric softeners used in the sheets, pillow case, and pj’s?
Should you eat before you sleep? What is the impact of watching television before sleep? Should you take sleeping pills to help you sleep?
These are some of the culturally defined issues that help determine how we sleep, all of which may have some potential impact on health. However, there is one cultural issue that tops the list of importance, and which may greatly determine your health status. It has to do with your sleep position. Are you sleeping on a firm, flat bed, face down, with your nose and eye compressed against the bed and pillow? Or are you on your back with your head slightly elevated, as is the case for many native cultures that use hammocks or other non-flat surfaces for sleep?
The reason we ask this last question is because the circulation to the head and brain is completely related to your body position when sleeping.
We all have had a time of experiencing dizziness or lightheadedness when getting out of bed too quickly. This effect is called orthostatic hypotension, and results from the fact that blood pressure falls when you lie down, and sudden raising of the head may temporarily deprive the brain of sufficient blood pressure, resulting in the dizziness or lightheadedness. The blood pressure soon rises, increasing the blood supply to the brain, as you feel normal again.
This phenomenon shows that the body’s position, relative to gravity, influences head and brain circulation. You can also demonstrate this by doing a head stand, which many yoga practitioners do daily. Intracranial pressure rises dramatically, as blood rushes to the head, which becomes beet red, and the neck veins swell out, as blood pools in the venous system.
But apart from these examples, very little, if anything, is mentioned in medical physiology Textbooks about gravity and its impact on circulation. Yet, you cannot fully understand brain circulation without considering gravity.
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 possibili
