#4 Posted Jan 24, 2010 - 9:28 PM:
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:
http://www.sfn.org/siteobjects/pub...F/ ... ctober.pdf
Pathophysiology of headaches:
http://www.merckmedicus.com/pp/us/...ne ... gy_sub.jsp
Headache movie (simplified):
http://www.davidson.edu/academic/p...ap ... .htm#movie
Vitamin D:
http://www.britannica.com/bps/addi...fo ... ery-Health
Edited by Landlady on Jan 24, 2010 - 9:34 PM. Reason: added links
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