Gassmann Lectures on High-Altitude Physiology
Photo: Chia-Chi Charlie Chang
People are naturally adapted to live at or close to sea level, where the body’s oxygenation is more optimal than in higher-altitude environments, said Dr. Max Gassmann in the Clinical Center’s FAES Education and Conference Suite recently. But for those who do not, acclimatization is possible.
“Every single cell in your body is able to sense reduced oxygen supply,” explained Gassmann, chairman of the University of Zurich’s Institute of Veterinary Physiology and the Zurich Center for Integrative Human Physiology in Switzerland.
Usually, a person can acclimate to higher-altitude conditions, but it can take up to 10 days to do so. Ideally, a person should begin his or her ascent to higher altitudes at 2,500 meters.
Gassmann advised that each day, one should climb 500 meters, descend 200 meters and then go to sleep. It’s difficult to slowly acclimate because it takes time and money. Additionally, there might not be a good place to pitch a tent on a steep mountainside.
During the adaptation period, red blood cell production increases. In places where oxygenation is reduced, a person’s kidneys will secrete the hormone erythropoietin. The hormone travels through the bloodstream to the bone marrow, where it spurs production of red blood cells. Gassmann noted that this process requires iron. Most iron in the body is found in hemoglobin, a protein that transports oxygen. Hemoglobin is contained in a red blood cell. The protein binds oxygen in high-oxygen areas, such as the lungs, and releases it in low-oxygen tissues. When abundant, iron is stored in the liver.
Iron is an essential nutrient, at the right levels. Too little causes anemia, while too much causes hemochromatosis. People with anemia do not transport enough oxygen in the blood. As a result, they feel tired and weak. According to the World Health Organization, anemia affects almost a quarter of the world’s population.
Hemochromatosis is a condition where a person absorbs too much iron from food, Gassmann said. If severe, symptoms include fatigue, weight loss and joint pain. Treatment includes removing blood from the body (usually via blood donation), chelation therapy and low-iron diets.
To ensure the correct amount of iron enters the bloodstream, the liver produces hepcidin, a protein that regulates the entry of iron into the circulatory system. When hepcidin is suppressed, more iron is released from the liver and directed to the bone marrow. The intestines also release higher levels of iron from food passing into the circulation.
Failing to acclimate increases the risk of developing acute mountain sickness, which begins to occur at 2,500 meters above sea level. Symptoms include headache, nausea and fatigue. Gassmann said the condition is like “somebody is squeezing your brain.” When someone experiences acute mountain sickness, it’s important to get him or her to lower altitudes as soon as possible.
Photo: Chia-Chi Charlie Chang
There are a few populations around the world who have adapted to higher altitudes, including Andeans and Tibetans. Each population has a different mechanism that allows them to function.
Populations that live in the Andes of South America adapt by producing more red blood cells to transport oxygen. However, this adaptation can lead to chronic mountain sickness. One of the classic symptoms of chronic mountain sickness is polycythemia, a condition where bone marrow produces far too many red blood cells. Blood becomes thicker and doesn’t travel through blood vessels easily.
Polycythemia increases the risk of heart attack and stroke. Affected individuals also suffer from pulmonary hypertension. Treatment involves moving patients to lower altitudes, which many don’t want to do for family reasons, Gassmann noted.
Tibetans, on the other hand, have a mutation that reduces the biological response to low oxygen supply. They present with higher lung capacity and use energy as efficiently as possible. He noted their ancestors have lived on the Tibetan plateau—which, on average, is 4,000 meters above sea level— in isolation for 3,500 years already. Thus, evolution had enough time to proceed. Tibetans don’t get chronic mountain sickness.
Even though these populations can live at high altitude, others will never be able to live in or even visit there.
“Training doesn’t mean you’ll reach a summit even if you’re in the best physical condition,” Gassmann cautioned. “Some people will never get acclimatized to high altitudes.”