Researchers Scale Answers on High-Altitude Headaches
Yale University scientists who monitored Mt. Everest climbers say they have new clues to what causes a rather ordinary affliction--the high-altitude headache.
The evidence indicates that people don’t get headaches at high altitudes because of less oxygen in the brain, as the researchers had believed, but because of overwhelming blood flow to the brain.
“We know categorically that in high-altitude headaches, the mechanism is different than what we thought all along,” said Dr. Richard Satava, professor of surgery.
Many people suffer headaches on the upper floors of tall buildings, while driving through mountains or riding in airplanes.
The research could help lead to treatments for the common headache and the more severe migraine, and help doctors better understand normal fetal development, some experts say.
The treatment commonly available for high-altitude headaches is a diuretic and respiratory stimulant called Diamox. But it is not effective in all cases.
Many mountain climbers can adjust to the altitude gradually as they climb. Some wear masks attached to oxygen canisters, but those don’t always provide enough oxygen. Others simply can’t adapt.
On Everest, a lack of oxygen, or hypoxia as it is known, is often accompanied by intense headaches that can impair decision-making, cause sluggishness and disorientation, and hinder coordination. Some people can die suddenly from cerebral edema--swelling of the brain.
“I’ve known a lot of people who have these bad headaches,” said Ed Viesturs, star of the IMAX movie “Everest” who has reached the peak of Everest, 29,028 feet above sea level, five times. “There are many who, their vision starts to blur, speech gets slurred. . . . They lose their balance. They’re not rational.”
In those situations, climbers have to be carried down to where a helicopter can land and take them away, Viesturs said.
“They don’t have a sense of what the lack of oxygen can really do to you almost until it’s too late,” he said. “Maybe if they discover what the actual mechanism of the headache is, we could save some people’s lives.”
The researchers, who hope to publish their study in a peer-reviewed journal this fall, believe high-altitude headaches may be the body’s way of warning climbers to descend before the brain suffers terrible consequences.
In the study conducted last spring, doctors at Everest Base Camp, 17,500 feet above sea level, examined 38 climbers from various international expeditions, as well as native Sherpas who accompany the climbers.
Using a portable ultrasound device, researchers measured the rate of blood flow in the carotid artery to the head and compared that with the rate in the brachial artery that feeds blood to the forearm.
The data showed a fourfold increase in the flow of blood to the head, said Dr. Ronald C. Merrell, chairman of Yale’s Department of Surgery.
The climbers adapted to the low oxygen flow in a variety of ways.
Some breathed harder, gasping for air at the higher altitudes. The bodies of others automatically increased the number of blood cells in the bloodstream. And others--those who had headaches--experienced a marked increase in blood flow to the brain. Some climbers experienced a combination of the three conditions.
Principal researcher Dr. Christian Macedonia said the increased blood flow to the brain was a way to compensate for the low levels of oxygen on Everest.
“We each have our own little scheme for adapting to the environment,” said Macedonia, an Army major who practices at the Walter Reed Army Medical Center in Washington.
Some who get headaches suffer mini-strokes. Other climbers experience lapses in short-term memory while on the mountain or long periods of forgetfulness after being on the mountain.
Similar research has been conducted on animals. Earlier this year, faculty at the University of Buffalo studied sheep that were placed in a pressurized chamber. Cerebral blood pressure forced apart cells and allowed fluids to accumulate in and around brain tissues, causing swelling of the brain.
UB neurologist Dr. Daniel Rifkin said the findings of the Yale study, the first in such an inhospitable environment, did not surprise him.
“It’s almost like brain congestion,” Rifkin said. “We don’t really know the ramifications of long-term exposure to low oxygen levels. We need to find ways to protect those tissues.”
Dr. Keith Campbell, editor of the journal Headache and former president of the American Assn. for the Study of Headache, said the Yale findings make sense. But because this was the first time carotid blood flow was measured in people in such conditions, he said, he would like to see further research.
“The lack of oxygen would have to change some mechanism in the brain,” he said. “It throbs. You know there’s more blood going through your head because of the pounding sensation.”
Campbell said the findings may shed light on methods to treat some form of migraines.
Macedonia, who specializes in obstetrics and gynecology and teaches at Georgetown University, said the research also may answer questions about fetal development. He noted that babies who have a weak placental connection to the mother often are born with well developed heads but withered bodies.
“The fetus has to do all sorts of things to extract oxygen from the mother through the placenta. When the placenta becomes sick, the fetus still has to get oxygen to the brain, and the brain will overcompensate at the expense of the rest of the body,” he said. “The environment in utero is a lot like being on Mt. Everest.”
