Atmospheric Pressure and Physiological Change
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Posted Jan 16, 2010 - 10:46 PM:
Subject: Atmospheric Pressure and Physiological Change
I have noticed that sometimes I feel tired/sleepy right before it rains, when the atmospheric pressure is dropping; and if the change in weather is rapid or dramatic enough, I sometimes get a headache. I've always been perplexed by this phenomenon and wanted to know exactly what's happening. I've heard that some older people, or people with joint problems also experience pain in their joints/bones right before it rains. I looked around for a detailed explanation and the best one that I came across stated that the bone tissue tends to expand and contract with pressure changes and when the air pressure drops, the bone tissue expands and tends to press on the surrounding nerves, thus causing pain. Now, I do not know if that's really what happens but it's one physical explanation that made the most sense to me. But how does that work with headaches? Exactly which part of the brain is being most affected by pressure change? What exactly happens physiologically to the body to cause these symptoms? Anybody has any ideas?
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Posted Jan 17, 2010 - 5:02 PM:
"Aching joints and changing weather" presents an interesting epistemological problem. "How do we know that there is a causal relationship between the weather and our aching joints?
The explanations I like the best is: A relationship between aching joints and changing weather may exist, but it is difficult to observe any such connection because (a) joints ache frequently and (b) the weather changes constantly. A strong correlation between weather changes and joint pain will probably be found if careful records of pain and weather conditions are kept. BUT: Correlation and cause are two completely different things. Finding a causal relationship requires a theory about the mechanism by which the changing weather causes joint pain, and then this theory needs to be tested experimentally.
You present the expanding bone theory. I don't know if your theory is true; I doubt it, but you could test this theory in a couple of ways.
On a day when the weather conditions are stable, especially having steady barometric pressure, proceed to a building that is around 100 stories tall. Stand in front of the express elevator door and note your feelings of pain very carefully. Write down what you feel. Take the express elevator to the observation deck on the top floor (where you will experience reduced air pressure because of an altitude change.) Again, carefully evaluate any sensations of pain you have. Write down what you feel. Use a pain rating scale. Do the same thing when you get back to ground floor. Repeat 100 times. Arrange for 100 friends, relatives, and acquaintances to perform the same experiment. Analyze the pain rating scales statistically and read all 10,000 written reports. OR
arrange for a ride in a small plane or helicopter. When you are sitting on the ground, carefully note your state of joint pain. Describe your condition and use a pain rating scale. Direct the pilot to take you to a height of 1.5 miles (7500 feet) and to remain at that level for 1 hour. At the end of 1 hour repeat the recording of pain sensation using a pain scale and written description. Repeat 100 times, and arrange for 100 friends, relatives, and acquaintances to do the same experiment in the same way, recording the same kind of information and analyzing the results. OR
Instead of using a tall building or an airplane, use a barometric pressure chamber.
This is all very complicated and time consuming. Maybe you could do some research at a university library or on line. Some questions to ask:
Are bones sufficiently expandable and compressible to press on nerves? (Are we talking about nerves in the bone or surrounding the bone?)
Are blood vessels sufficiently expandable and compressible to press on nerves? (Probably they are. I believe that certain kinds of headaches are caused by expanding and contracting blood vessels in the scalp. The adult bones of the skull are fused together and significant expansion or contraction is probably not possible.
Do pilots who fly in unpressurized planes experience joint pain during or after their flights?
When people are under water at depth for extended periods of time (like divers using oxygen gear) do they experience joint pain as the result of changing pressure (NOT talking about the bends here)?
I have mild age related osteo arthritis and experience joint pain fairly often. I don't keep track of it very carefully, but I do know that activities that strain the joints (like carrying groceries 1 mile from the store to home) causes joint pain over the following day or so. Walking several miles will result in knee pain. Not walking anywhere for several days also produces knee pain. I live in Minnesota. The center of the continent has more or less constantly changing weather.
There is another source of joint pain that needs to be accounted for, and that is the internal conditions of our body. Is something happening inside your body (not related to the weather or activity levels) that could cause joint pain. Are there immune system functions that can trigger joint pain? Cancer? infections? Parasites? Injury? physical causes such as structural problems in the bones or joints?
The upshot is that blaming joint pain on the weather is an upshot in the dark.
Edited by BitterCrank on Jan 17, 2010 - 5:08 PM
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Posted Jan 17, 2010 - 7:57 PM:
Headaches are associated with the protective layer around the brain, the minenges, and to some extent migraines have also been associated with microscopic holes in the heart. As the air pressure drops presumably the minenges swells creating pressure on pain receptors, while the brain itself has no pain receptors. However, the exact pathology of headaches remains unknown.
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Posted Jan 25, 2010 - 12:28 AM:
I did some research on different existing theories that explain what might be causing the drowsiness and headache. My initial guess was that the barometric pressure causes an imbalance between the intracranial pressure and the rest of the body (along the lines of Monro-Kellie hypothesis), and the symptoms were somehow related to an attempt to equalize the pressure. So, I assumed the culprit was the pressure itself. Many of the explanations involving correlations between weather and headaches that I came across, however, point to possible changes in oxygen levels in the atmosphere, combined with the vascular theory as a main triggering mechanism.
The brain hypoxia theory suggests that a change in barometric pressure causes changes in oxygen levels in the atmosphere, which in turn cause changes in the blood oxygen levels. To compensate for lowered oxygen, the blood vessels dilate to bring more blood flow to the brain. There are many things that can cause blood vessels to dilate, of course, including diet and hormonal changes, but a change (decrease) in the blood oxygen would also have the same effect on the vascular system, namely vasodilation; and considering that one of the constants in all of the cases is the drop in atmospheric pressure, it would seem natural to assume that lowered oxygen level might definitely be a triggering mechanism. This could be easily corroborated (or alternatively, refuted) by monitoring of oxygen concentration in the air as the air pressure changes to see if, indeed, there is a decrease in oxygen concentration in the air as air pressure decreases.
Although it’s true that most of the brain is insensitive to pain, there are some sensory nerves that surround intracranial blood vessels, and as the blood vessels dilate they activate sensory nerves (in this particular case, the activation of trigeminal sensory nerves/Nerve V is suspected), thus causing a perception of pain. It was also mentioned that activating trigeminal nerves triggers the release of certain vasoactive neuropeptides which act as vasodilators, which further aggravate the symptoms.
The proponents of vascular theory point to the fact that when the patients are given vasodilators, the symptoms of the migraines got worse, and when they were given vasoconstrictors, the symptoms were diminished. This points to the fact that vascular theory definately plays a role in triggering headaches.
The hypoxia theory seems plausible to me for several reasons. One of the symptoms of brain hypoxia is drowsiness, which is one of the first things that I notice when the pressure is dropping. There are some studies which show that brain hypoxia is often a precursor to many migraines, as well. The hypoxia theory would also explain why this happens only when the pressure is dropping and not when it’s rising. And this theory is the only thing so far that could explain this fact.
However, I am mindful of the possibility that there could be some other contributing factors, as well. If pressure drop was the sole factor then I would have a headache every time there was a pressure drop, which is not usually the case. Some other factors that were mentioned were hormonal changes, especially change in estrogen levels. It’s possible that the pressure drop coincided with an estrogen drop and that somehow played in. It’s been shown that drop in estrogen levels leads to a drop in serotonin levels, which in turn cause the trigeminal system to release the same neuropeptides which cause vasodilation (specifically substance P). This was one of the explanations given as to why women are more susceptible to headaches/migraines then men.
I also came across an interesting study in which people who suffered from frequent migraines were shown to have low levels of vitamin D in their blood, so there might also be a relevant component of nutritional deficiency that might affect vascular health and contribute to sensitivity/pain. I haven’t had the time to look more in depth into this, but I think it would be interesting to follow this up, or at least keep it in mind.
Some sources, if you’re interested:
Vasodilation and Headache:
Pathophysiology of headaches:
Headache movie (simplified):
Edited by Landlady on Jan 25, 2010 - 12:34 AM. Reason: added links
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