Posted by DocGreg on December 17, 1998 at 00:50:57:
In Reply to: DocGreg posted by Troy on December 15, 1998 at 21:19:16:
T,
Yes, oxygen causes vasoconstriction of the arteries in the brain. This is thought to be the mechanism of action in the treatment of cluster headaches.
The brain has a very complex mechanism for regulating how much oxygen get through to the brain tissue. During low oxygen levels, the arteries open up to allow a greater blood flow. When high levels are reached, it constricts down to limit the flow. So, saturating your blood with oxygen causes the constriction fo the blood vessels.
In some sorts of migraine headaches, when the arteries constrict before they open, oxygen is contraindicated, as it increased the risk of stroke. In cluster headaches, however, there is no preceding phase of constriction...so O2 is safe.
Exactly why constricting the blood vessels causes pain relief is not well known...but many of the abortive drugs (including the ergotamines, the triptans like imitrex, all cause constriction of the vessels).
Hope this helps
G