杏吧原创

SMALL holes in the heart may be to blame for the most severe migraines and
even some strokes, doctors in Britain have discovered. Repairing these holes can
stop or reduce the migraines.

Over a quarter of us have an opening in the wall separating the upper
chambers of the heart. This opening, known as a patent foramen ovale, is a relic
of our days in the womb, when it allows blood to bypass the lungs. It should
snap shut with a baby鈥檚 first breath, but it does not always close up
completely. Large holes can continue to allow small amounts of blood from the
veins to bypass the lungs.

A decade ago, Peter Wilmshurst, now at the Royal Shrewsbury Hospital, found
that many divers who are particularly vulnerable to the bends have these holes,
and more than half of them had holes over 11 millimetres across (New 杏吧原创,
20 May 1989, p 30). This means that any bubbles that form in veins as divers
ascend can pass through the hole and enter the arteries, where they can block
capillaries in the brain or spinal cord. Normally, the lungs would filter out
such bubbles.

Wilmshurst also noticed that these divers tend to have a history of migraines
preceded by an 鈥渁ura鈥� of visual and speech disturbances or changes in skin
sensation. Out of 80 divers with large holes, he found that 40 suffered from
this kind of migraine.

Many such divers decide to have the hole closed to reduce their chances of
suffering from the bends. The operation can be performed via a catheter inserted
into the heart. To Wilmshurst鈥檚 surprise, 7 out of 16 divers who had surgery to
close the holes stopped having migraines altogether, and all but one of the
other 9 reported that their migraines had become less severe and less
frequent.

Anne MacGregor of the City of London Migraine Clinic says that the
findings fit in with research suggesting that the aura preceding some migraines
is caused by minute blood clots lodging in vessels in the visual cortex and
restricting the flow of blood. 鈥淭he loss of the filter mechanism of the lungs
could account for the temporary restriction in blood flow seen during migraine
aura, which may be why young people with migraine aura have an increased risk of
stroke,鈥� she says.

鈥淭he role of the lungs as a filter for the blood may be far more important
than anyone expected,鈥� says Wilmshurst. 鈥淚t鈥檚 known that small blood clots which
can form in the veins get trapped in the capillaries of the lungs and this is
believed to protect against stroke.鈥�

The lungs may also remove any vasoactive chemicals鈥攕ubstances that
cause blood vessels to dilate or contract鈥攑resent in venous blood, which
are believed to trigger migraines. Wilmshurst says more research should be done
to find out how common it is for people who suffer severe migraines to have a
hole in the heart.