Advancing the Science

Mayo Clinic Medical Science Blog

May 28th, 2012

The Why of Researching on Everest


Dr. Bruce Johnson explains about researching in extreme environments:

Our research laboratory has a long history of studying the limits of human performance and human adaptation in extreme environments. This has a number of practical applications, such as the deployment of troops to these environments (like Afghanistan – cold, high and dry) or workers that are exposed to extreme conditions (e.g., South Pole where up to 700 workers are exposed each year, oil industry in extreme northern latitudes, numerous observatories that are located at high altitudes as well as the general outdoor sports/tourist industry).  Attempting to study and mimic the conditions humans are exposed to in their respective environments in the laboratory is difficult if not impossible and thus there is a long history of scientists working in the field, which truly is the ultimate laboratory where human physiology and environment come together.  In the human condition, there are few chambers in the world that can mimic the hypobaria of high altitude, temperature fluctuations, humidity as well as the interaction with human factors (e.g., dehydration, physical activity, psychological stress) in free living people.  Thus the majority of our work is a combination of laboratory studies where conditions can be highly controlled as well as field work.

We have previously pursued studies in world class endurance athletes (runners), in workers at the South Pole, on acclimatizing subjects on Mt Aconcagua in Argentina and in breath hold divers in Croatia.  It has been quite interesting what has been learned from these field studies, including treatments that have been used for preventive measures and primarily studied in the laboratory but which did not produce the same results in the field condition. In addition, novel and unexpected applications for clinical use have also come from these field studies.

Everest was a project that had a number of goals.  One was collaboration with The North Face Company to help study apparel and equipment in field conditions in order to improve products that would ultimately improve human performance in extreme environments.  Another goal was to attempt to decipher differences between hypobaric and normobaric hypoxia.  The only way to simulate hypobaric hypoxia is through a chamber or ascent to high altitude.  Finally a number of studies suggest that an increase in extravascular lung water is common at high altitude (HAPE, high altitude pulmonary edema), a finding that is opposite to our findings in the laboratory.  Risk factors for HAPE include heavy physical activity, rapid ascent, the actual altitude and possibly sleep abnormalities. It is difficult if not impossible to put 20 people in a chamber (10 that have acclimatized for 6 weeks) and 10 that are going through the acclimatization protocol for anther 4 weeks, mimic the conditions surrounding high altitude and subsequently allow normal movement and living conditions.  Understanding and studying the unique differences in physiology across cultural groups is also difficult to perform in a lab back in Rochester, MN.

It is interesting the synergies between patient populations, such as heart failure (leading cause of hospital admissions in people over age 65 yr) and healthy humans exposed to severe hypobaric hypoxia (high altitude).  For example, the low partial pressure of oxygen in the air stimulates the peripheral chemoreceptors setting off a host of physiological changes, such as stimulating the sympathetic nervous system, altering autonomic function, driving sympathetic nerve activity and increasing neurohormones in the blood.  There is an interplay between the peripheral and central chemoreceptors (in the brain) that causes periodic breathing at night with severe drops in oxygen levels in the blood – apneas.  The low inspired oxygen also causes the blood vessels in the lungs to constrict, increasing the work on the right side of the heart and though the mechanism is still debated, fluid can build up in the lungs causing the life threatening condition of HAPE.  Interestingly in heart failure, the low perfusion caused by low cardiac output reduces shear stress forces at the carotid body (peripheral chemoreceptors) which is sensed similar to low oxygen.  The low output of the heart also reduces perfusion to tissues, which is also sensed like low oxygen.  Heart failure patients have marked increases in sympathetic nerve activity – similar to high altitude, a shift in autonomic function, a marked rise in neurohormones (like the person at high altitude), develop central sleep apnea (like high altitude), develop high blood pressure in their lungs and typically come into the emergency room with lung congestion (fluid in the lungs).  The parallels have allowed mechanisms learned from high altitude studies to be transferred to our work in the heart failure population and vice versa.

Finally, there is nothing more exciting or important then my role as a mentor for younger students.  Thus, the goal is not only to teach solid research practices, grant writing skills, laboratory techniques as well as physiology, but to excite and encourage the next generation of scientists.  Many students have been discouraged by long days in the laboratory often at the “bench” and though this is still the typical pattern for most research laboratories, our approach is occasionally use the world around us as a laboratory for the young students that join me on these exciting opportunities.  It was what originally motivated my interest in science and got me excited about the ideas we chase in the laboratory today.  Hopefully we will continue to excite and encourage a new generation of scientists that can reach back to basic science, but can also integrate and translate new and novel ideas into the complex human being.

To truly understand the work being done with athletes summiting Everest, one would need to dig deeply into the rich history of altitude research, our many years of work in mechanisms of lung physiology and fluid regulation in health and disease and the growing need for researchers in the field of integrative human physiology.

Bruce Johnson

Tags: altitude research, Events, Findings, Innovations, Mayo Clinic, Mount Everest, National Geographic, People, physiology, Progress Updates, research education, science education, The North Face, Uncategorized


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