Does Your Heart Pine For the Mountains?

While planning a trip to the Andes Mountains, I wondered about the effects of high altitudes on the heart.  Are high mountain elevations bad for the heart? Are there beneficial effects to the heart and exercise fitness for those living at high elevations?

With ascension to higher elevations, a variety of illnesses can occur, including acute altitude sickness, high altitude pulmonary edema (HAPE, fluid in the lungs, similar to congestive heart failure) and high altitude cerebral edema (HACE, swelling of the brain). High altitude is defined as 4,900 to 11,500 feet (for example: Mount Washington, White Mountains, New Hampshire), very high altitude is 11,500 to 18,000 feet (ex, Pikes Peak, Rocky Mountains, Colorado) and extremely high altitude is greater than 18,000 feet (ex, Mount McKinley, Alaska).  As altitude increases the available amount of oxygen progressively decreases until the "death zone" is reached at about 26,000 feet (for example at the summit of Mount Everest). In the death zone, the amount of oxygen is so low that life is not sustainable without the use of supplemental oxygen through oxygen tanks. In the body, the oxygen we breathe in is bound to hemoglobin, a compound found in red blood cells. The oxygen bound to hemoglobin is carried by the blood throughout the body and released for use.  At sea level, oxygen optimally saturates the hemoglobin. At high altitudes, the oxygen saturation of hemoglobin drops significantly, and the body feels "oxygen deprived". This would be similar to being trapped in a smoke filled room and not having enough oxygen to breathe. The body compensates for the lack of oxygen by increasing the breathing rate (hyperventilating), increasing the heart beat, increasing the amount of blood the heart pumps, producing more red blood cells and shunting blood away from nonessential functions (for example digestion is more difficult at high altitudes).

With rapid ascension from sea level to high elevations, acute altitude sickness may occur, especially for heights above 8000 feet. Symptoms include headache, nausea, vomiting, weakness, dizziness, swelling of the hands or feet, and shortness of breath with exertion. Acute altitude sickness symptoms are usually temporary and improve with hydration and as the person "gets used to" the elevation, a process called altitude acclimatization. Ascending slowly is the best way to prevent altitude sickness. Altitude acclimatization is routinely used by mountain climbers and includes ascending about 1000- 2000 feet at a time (once above 8000 feet) for several days and allowing the body to acclimatize to the lower levels of oxygen at the higher elevation. Once the body has adjusted to the new elevation, the process is repeated at progressively higher altitudes. For a climber attempting to reach the summit of Mount Everest, acclimatization can take several weeks.  In addition to acclimatization, other prophylactic measures include aspirin, ibuprofen or acetazolamide (a diuretic). 

High altitude pulmonary edema (HAPE) develops after two or more days at altitudes greater than 9000 feet. The risk increases with higher altitudes and faster ascent.  If left untreated, HAPE is fatal in 50% of cases. The symptoms include shortness of breath with exertion, dry cough, gurgling in the chest and pink frothy mucous. Despite symptoms similar to congestive heart failure from a weakened heart muscle, HAPE occurs due to high pressure in the lungs with leaking of fluid from the small vessels in the lungs into the lung tissue. Since the mechanism is different, it is treated differently than conventional congestive heart failure. Diuretics are not used, but oxygen and medications that reduce the pressure in the lungs are given. Immediate descent to lower altitudes is lifesaving. There appears to be a continuum from acute mountain sickness to HAPE to HACE and precautions to avoid acute mountain sickness reduce the risk of the more serious HAPE and HACE.

Patients with established heart disease need to be cautious at high elevations. Angina, chest pain due to heart artery disease, can worsen at altitude due to the increased demands on the heart. If a coronary stent is being planned, this should be done prior to travel. Patients with stable coronary artery disease and little or no angina with exertion at sea level can likely tolerate elevations to 8000 or 9000 feet.  Patients with congestive heart failure, unstable chest pain, pre-existing high pressure in the lungs or unstable rhythm diseases should not ascend to greater than 6000 feet. 

Can living at a high altitude be beneficial? Why do so many endurance athletes come from the mountainous countries of Kenya, Ethiopia, Uganda or countries in the Andes and Himalaya mountains? Why is the United States Olympic training facility located in the Rockies in Colorado Springs? The same effects the body goes through while acclimatizing to high altitudes occur in people who live at high elevations full time. Some of these effects are quite beneficial for heart performance and endurance athletics. For instance, the amount of blood the heart pumps with each beat is greater in those living at high attitudes. In addition, the body manufactures additional red blood cells to carry more oxygen (this is similar to “blood doping”, the method of cheating Lance Armstrong was accused of during his Tour de France wins).  Both of these adaptations have the same effect, to increase the amount of oxygen available to exercising muscles. So living at high elevations can give an edge in athletic performance.  However, training at high altitudes offsets these beneficial effects, essentially negating them, as athletes cannot train with same intensity at elevation that they can at sea level. That is why athletes, “live high and train low”; they live at elevation and do their training a lower attitudes.

So if you are lucky enough to live at a high elevation, start training at sea level; you could become an Olympic star. If you are visiting the mountains, take precautions and enjoy the views.