Only a few days ago I went hiking in Colorado’s tall Front Range Mountains. Man, was I in for a doozy! Coming from Raleigh, North Carolina, where the elevation is a mere 315 feet (or 96 meters), I was warned of the symptoms that may occur as I stepped off the airplane in Colorado Springs, elevation 1,893.5 m. To acclimate myself to the high altitude a friend suggested we first travel to the nearest mountaintop: Pikes Peak, elevation 4,302 m. As we neared the top in our rent-a-van, I notice that I was breathing faster, which made me lightheaded and fatigued. As my head pounded, I asked myself: How do people live up here? Are they born with superpowers?
Yes, genetic superpowers! Anthropologist and cardiologist at the Case Western Reserve University in Ohio study Tibetan and Andean populations because they have evolved to cope with the continual stress of high-altitude-living. Evidence of Darwin’s theory of natural selection happens every day in these two very separate regions of the world. Exhibit A:
Hearty, healthy babies.
A study by Cynthia Beall shows that because of generations of adaptive genes, mothers on both continents have heavier babies due to a successful increase of oxygen delivered to their uterus and placenta during pregnancy. This is a great accomplishment because in altitudes as high as the Tibetan Plateau (average 4,500m) oxygen is hard to come by.
Lowlanders, like me, on the other hand travel to such elevations in constant fear of altitude sickness. Climbers and mountaineers all over the world can relate. In fear of altitude sickness, and potentially fatal conditions like pulmonary hypertension, these adventurers take a combination of drug-store-bought Diamox (to relieve blood pressure) and Viagra (to dilate blood vessels). Diamox however is a diuretic and can lead to dehydration, whereas Viagra tends to mainly affect just a localized area. ;)
Altitude sickness, called “high-altitude hypoxia” by the medical world, is very common in lowlanders. High-altitude hypoxia is a term that refers to the human response to less than normal amounts of oxygen in the atmosphere. Incidentally for lowlanders their physiological response doesn’t make much sense. The body kicks into survival mode, realizing the need for oxygen. Quickly, blood vessels constrict in order to efficiently direct the available oxygen to the most important places in the body. Exhaustively, your body demands that you take more and more breaths to deliver the same amount of oxygen to your bloodstream. Though as you climb in altitude, atmospheric pressures drops, meaning that there is less available oxygen in the air. The resulting lowlander is apt to look and function like a modern day Frankenstein. It can take weeks, and even months, to acclimate to these high-altitude conditions. 
Dr. Michael Callahan, program manager at the Defense Advanced Research Projects Agency (DARPA), recognizes the need for function at high altitudes. Employed and funded by the US Department of Defense, Callahan’s knows that researching ways to speed up the acclimatization process could immediately aid our troops involved in mountain warfare abroad. Understanding exactly where adaptations can be made is highly important for research.
Beall’s study revealed that Andeans and Tibetans (at ~3,700m) accomplish healthy reproduction using two different pathways of evolution. While similarly maintaining regular basal metabolic rates (minimum amt energy needed to regulate body temp, heart rate, breathing), upholding maximal oxygen uptake and common range of oxygen delivery to organs; these populations breathed at different rates, their blood flowed at different rates and the had differing levels of hemoglobin in their blood. Hemoglobin is important because it acts like velcro to oxygen, carrying it into the mitochondria of each cell for energy production.
On exposure to high altitude, Tibetans retained the (lowlander) trait of increased ventilation, which sustained persistent levels of hypoxic stress. Yet, because of less velcroed hemoglobin there were lesser amounts of the oxygen content in their blood. Nevertheless, they consistently displayed low blood pressure.
According to Jonathan Stamler, cardiologist and funded DARPA researcher at the Case Western, nitric oxide that binds to hemoglobin helps regulate blood vessel dilation, which “helps explain the healthy blood flow of Tibetan highlanders.” DARPA has released pilot experiments that demonstrate that by inhaling eythl nitric oxide, one can improve their blood oxygenation.
Andeans on the other hand breathe slower and receive greater intake of oxygen into their blood. Due to greater amounts of a protein called Erythropoietin, a builder-block that boosts hemoglobin, their blood pressure is consistently well above average. Thus, they are all prone to cases pulmonary hypertension from day one.
Erythropoietin is infamously known as the performance-enhancing drug abused in the Tour de France. What happens if these adaptations become available to a larger audience?
Scientists all around the world are coming closer and closer to alienating the specific genes that are associated with these adapted traits. But as climbers continue to climb, troops to scale and Tibetans to breath, we all must remember the motivation behind our ascent. What will happen if humans adapt to living at all altitudes?
References:
Beall, Cynthia M. "Two Routes to Functional Adaptation: Tibetan and Andean High-altitude Natives." PNAS 104.May (2007): 8655-8660. Print.
Borrell, Brendan. "Mountains to Climb." Nature Medicine 16.11 (2010): 1176-1179. Print.
No comments:
Post a Comment