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's 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.
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. 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.