By Helen K. Kelley
Altitude sickness, also called acute mountain sickness, is caused by climbing or walking to a higher and higher altitude too quickly, not giving the enough time to adapt to the lower air pressure and oxygen level in the higher elevation. To understand more about altitude sickness and how to prevent or treat it, we spoke with three Atlanta area physicians who shared their expertise and experience.
Symptoms, prevention and the heart of the matter
At higher altitudes, the barometric pressure decreases, resulting in fewer oxygen molecules available to breathe, ultimately resulting in decreased oxygen delivery to tissues. According to Andrew Smith, M.D., a cardiologist and Medical Director of the Advanced Heart Failure Program at Emory Healthcare, this decreased oxygen availability causes a number of physiological symptoms identified with altitude sickness.
“With the decreased oxygen availability to the tissues, the result is an increased release of adrenalin, which can cause increase in heart rate and also possibly an increase in pulmonary artery pressures,” he said. “Additionally, what occurs within this is an increase in respiratory rate, and therefore, hyperventilation occurs, at least initially. Resting heart rate increases. Often the humidity tends to be lower at high altitudes, so, along with the increased adrenaline drive, there is a tendency to become dehydrated.”
Along with dehydration, people who are experiencing altitude sickness may have symptoms like mild headaches, nausea, more rapid breathing, fatigue and difficulty sleeping at night. In fact, because the breathing rate tends to be lower when sleeping, the lower level of oxygen delivery to the tissues can put more stress on the body at night.
Smith adds that more serious symptoms can occur at extreme altitudes in both normal people and those with genetic predispositions or health issues.
“For example, high altitude pulmonary edema can happen to anyone. If you develop a bad cough, become short of breath or cough up frothy sputum, that is a sign,” he said. “High altitude cerebral edema, or HACE, can cause a change in mental status, with symptoms like worsening headaches, lethargy, ataxia and confusion. ‘Leaky capillary syndrome,’ in which fluid leaks out of the capillaries in lungs, can also occur in the brain. Symptoms like these indicate you need to get down to a much lower elevation and seek medical attention immediately.”
For those who are traveling to higher elevations, Smith says there are a number of measures they can take to prevent the symptoms.
“Hydrate well and travel slowly to different degrees of elevation, so that some degree of acclimation occurs every few days. If you’re going to be doing something strenuous at a higher elevation, take breaks,” he advised. “Hiking and climbing to higher levels may be fine, but not camping and sleeping there. You can also prepare by getting yourself in better physical condition before you go.”
Most of all, common sense should prevail, especially for people who lead a sedentary lifestyle or who haven’t gotten regular check-ups.
“Travel to a high altitude location can unmask preexisting heart disease. I’d advise anyone planning to do so and who hasn’t been exercising regularly, to see a physician in advance for a cardiac stress test. Chest pain, angina, persistent shortness of breath… those are all warning signs,” Smith said. “Of course, for patients who have known heart disease, travel to high elevations can be extremely risky. It’s important that they recognize that they will be in situations where they don’t have control of their environment; environment will be controlling things like their heart rate response.”
One physician’s personal experience
Allen Dollar, M.D., Associate Professor at Emory University School of Medicine and Section Chief of Cardiology at Grady Memorial Hospital, has been an avid backpacker since his teens. In recent years, Dollar and two friends have made an annual trip to Colorado to go hiking in the San Juan Mountains. It was there that he experienced altitude sickness for the first time in his life.
“The first year we made the trip I had no problems, but the second year, we ascended more rapidly from the ground level — we went from 6,500 ft. to 13,200 ft. in just two days,” he recalled. “I became sick as a dog. Basically, altitude sickness felt like the worst hangover you could ever have.”
While the treatment is to immediately descend to a safer level, Dollar and his friends were on the far side of a ridge that meant ascending another 500 ft. on a treacherous trail before being able to travel downward. It took an additional 24 hours before Dollar felt well enough to make the ascent and the descent.
He says that he was fortunate not to experience worse symptoms.
“I never developed shortness of breath or high-altitude cerebral edema,” he said. “My friends tested my mental clarity with math problems to be sure I was all right.”
Dollar said that one of his group had been taking Diamox (acetezolomide), a drug that been shown to help in preventing altitude sickness. After seeing his positive results, the others now begin taking Diamox two days prior to starting their climb and the regimen has proved successful.
He adds that there is no way to predict who will experience altitude sickness and who won’t.
“What I can tell you is that altitude sickness doesn’t have anything to do with a person’s fitness level,” he said. “You’re either susceptible or you’re not.”
Q & A: Altitude and the lungs
To learn more about how altitude affects the lungs, we asked Abubakr Chaudhry M.D., a pulmonary and critical care physician and specialist in pulmonary vascular diseases with Northside Hospital, to share his insights in a two-part Q & A.
Q. How does altitude affect breathing?
AC: In order to understand how altitude effects breathing, we first have to understand what happens physiologically when we experience rapid changes in barometric pressure, such as during an ascent from sea level (760 mmHg) to the summit of Mount Everest (253 mmHg) per say. It is important to note that there is not a depletion of atmospheric oxygen content at higher altitudes, but rather a change in the driving pressure of the gas in the lungs. The higher you go, the lower the barometric pressure, and thus the lower the driving pressure.
Next, we must understand how gas exchange occurs in the membranes of the lung and how our bodies react to this change in driving pressure. The decreased driving pressure results in tissue hypoxia, decreasing the substrate available for aerobic respiration and stimulating us to hyperventilate. This phenomenon can be quantified by the alveolar-ventilation equation, which demonstrates an inverse relationship between the level of alveolar ventilation and the alveolar PCO2 (if CO2 production is constant). Thus, the more we breathe the less CO2 we retain. Furthermore, at higher altitudes it has been reported that climbers can decrease their PCO2 from a normal value of 40 to a value of 8 ( five-fold!). This change in breathing patterns leads to respiratory alkalosis. Alkalosis has the deleterious effect of increasing hemoglobin’s affinity to oxygen but it also enhances the uptake of oxygen in the pulmonary capillaries, an effect that is highly beneficial in these individuals. With changes in breathing patterns comes the question of need for oxygen.
We used the extreme example of Mount Everest but most normal individuals will not need supplemental oxygen unless they are ascending above 6500 meters.
Q: What are some ways an individual with a lung condition can prepare for travel to a high altitude?
AC: If someone has an underlying lung condition and is preparing for high altitude travel, the best thing to do is see a pulmonologist to assess his or her “hypoxic ventilatory response.” As previously stated, the major physiologic change that occurs with ascent is hyperventilation. If a patient cannot decrease their carbon dioxide levels, it will be unlikely they will have the energy required to oxygenate well, either. Supplemental oxygen can help, but the amount needed will likely change depending on the barometric pressure (the elevation to which the person climbs). If the patient’s hypoxic ventilatory response is poor, I would recommend against high altitude travel.
Preparing for high altitude travel is possible, but not in the way usually advertised. There are a lot of gimmicks out there that promise to “increase your red blood cells” with “hypoxia training.” I do not recommend these even in normal individuals, as the physiologic change is transient. I do recommend safe intensive strength and endurance training with a plan that is doctor supervised. Particularly in patients who have underlying lung disease, not only does training improve mortality, but it also improves the hypoxic ventilatory response by maximizing the body’s utilization of oxygen.
To someone who is planning a climb and has been cleared by their doctor, I recommend remembering the climber’s adage of “climb high and sleep low.” This means you should acclimatize yourself progressively. Once you get above 3000m, try not to climb more than 300m a day and rest every third or fourth day. If you experience symptoms of mountain sickness, you don’t have to run down the mountain, but try to descend at least 500m. In most cases of acute mountain sickness this descent will resolve the symptoms.