Many athletes take advantage of altitude training to improve their performance. The lack of oxygen caused by altitude helps stimulate the production of red blood cells, which are responsible for transporting oxygen to the muscles in the body. However, beyond a certain point, these benefits become detrimental as the high number of red blood cells makes the blood more viscous, increasing resistance within the circulation, elevating blood pressure and forcing the heart to work harder. "When an abnormally high number of red cells persists permanently, even at sea level, we speak of the rare disease polycythemia. However, in persons who live permanently at high altitude, who for some reason produce too many red cells, the syndrome is called Chronic Mountain Sickness," explains Justin Lawley, Professor of Performance Physiology and Prevention at the University of Innsbruck. "These patients suffer from signs such as high pressure in the blood and lungs, circulatory dysfunction, and the perception that exercise or physical activity is extremely exhausting for them," Lawley continues.
Unique phenomenon in Cerro de Pasco
Chronic Mountain Sickness is particularly prevalent in the Peruvian mining town of Cerro de Pasco in the Central Andes. There, an above-average number of men have a highly elevated red blood cell count. What is astonishing is that previous research suggests that their exercise capacity, measured by assessing how much oxygen the body can utilize, is comparable to that of healthy inhabitants, at least in the first years with Chronic Mountain Sickness. From this, Lawley and his colleagues conclude that some Andean’s must have adapted to the viscous blood to some degree. "This unique phenomenon has so far only been demonstrated in this population in the Andes and it shows that exceeding the optimal hematocrit, by which we mean the proportion of red blood cells that is thought to be detrimental, does not always lead to exercise intolerance. With our investigations, we wanted to find out what physiological processes had changed to allow normal exercise capacity despite polycythemia," Lawley describes. To this end, the international team, which consisted of researchers from more than 20 Universities worldwide, performed a series of studies with the residents of Cerro de Pasco using the most modern and sophisticated research methodologies.
Blood components and blood pressure decisive
First, the scientists investigated how thick the blood of Andean’s with Chronic Mountain Sickness was and potentially why. Therefore, they took blood samples and performed a carbon monoxide rebreathing test to determine the proportion of plasma in the blood in relation to the number of red blood cells. "The result was surprising to us. For decades, it has been assumed that the main reason for the elevated erythrocytes in Chronic Mountain Sickness was that these Andeans breathed less and therefore lacked oxygen. However, our results show that the proportion of plasma was very low and therefore the increase in red cells maybe a compensatory mechanism to maintain blood volume. Unfortunately this turns the blood thick," Lawley says. In further studies, the researchers want to find out why this reduction in blood plasma occurs and whether there is a genetic mechanism for it. To do this, Lawley and his team will travel to Cerro de Pasco again next year and spend several months in the mining town. "We know that plasma volume can be increased by regular aerobic exercise. For example, the research team found that the so-called "king of the mountains," the Tibetan Sherpa, has a very large plasma volume, which allows them to maintain a red blood cell count comparable to that of lowlanders," Lawley reports. During their next research visit, the scientists therefore want to test whether exercise is a possible therapy for patients who have so far only been able to alleviate their symptoms by removing red blood cells or descending to lower regions.
Adaption for time
While the researchers' tests have shown that Andeans suffering from a mild form of Chronic Mountain Sickness can cope well, several of the tests also revealed worrying results. In complex examinations of vascular function, in which the researchers combine pharmacological infusions with microelectrodes placed in the sympathetic nerve, they were able to show clear differences between healthy and affected participants: "For example, although their blood pressure was normal at rest and they were able to perform exercise without any problems, we could see that their blood vessels were dysfunctional and they had to be constricted very strongly during exercise to maintain blood pressure. This constriction was much less in the healthy subjects," Lawley explains. These findings show that physiological adaptation to the disease polycythemia is probably only possible to a certain extent and that the Andean’s were utilizing limited resources. "The longer a person has the disease and the older they get, the harder it likely becomes for the body to maintain the adaptive mechanisms. The vessels become stiffer as a result of the aging process and are less able to respond during exercise," Lawley adds. Future tests will therefore also examine people with advanced Chronic Mountain Sickness. The researchers also want to find out how the heavy pollution from mining in Cerro de Pasco, one of the most polluted cities in the world, affects chronic altitude sickness. The expedition has already results in over 18 peer-reviewed publications, 5 involving researchers from the University Innsbruck.
Book on high-altitude medicine and physiology: Justin Lawley is a Professor of Performance Physiology and Prevention at the Institute of Sport Science at the University of Innsbruck. Lawley's research focuses on the physiology of human adaptation to stress (e.g. caused by exercise, low oxygen levels and changes in temperature, or zero gravity) and the use of this knowledge to improve human health and performance. In February of this year, he and colleagues published the sixth edition of Ward, Milledge and West's High Altitude Medicine and Physiology. The book addresses one of the focal points of Lawley's research, high-altitude physiology. The book is aimed primarily at sport scientists with courses in environmental physiology, physicians who prepare people for expeditions or who specialize in diseases and accidents at altitude, as well as physicians and physiologists who study human dependence on oxygen and the body's adaptation to altitude.