Banner by Colton Siatkowski

Up in the Air

By Varsha Sriram

As the saying goes, “the summit is optional, but the descent is mandatory.” From the final camp on Mount Everest, 7,900 meters above sea level, hikers must climb 900 meters before they reach the summit. This is known as “the death zone” since the environmental conditions created at 8,000+ meters of altitude cause the human body to deteriorate from the lack of oxygen, which is 33% less than at sea level. At these altitudes, it becomes every man for himself as hikers are in a race against time, forced to climb with decreased psychomotor functions, such as difficulty breathing and inability to effectively supplement oxygen. As a result, a vast majority of fatalities occur due to hikers overexerting themselves to perform basic tasks en route to the summit. In fact, 35% of all deaths on Everest occur after climbers have summited. One famous example of this is the 1996 Everest disaster, which showcased the devastating psychological effects of prolonged periods spent in the death zone: eight lives were lost in a single night. This disaster arose from a deadly combination of increased snowfall and hikers neglecting the scheduled descent time that stranded multiple victims in the death zone. Mountain psychosis was documented in radio calls from the group’s leader. Despite repeatedly stating he was starting his descent, he would shockingly radio in that he was still in the death zone 10 hours after the scheduled descent time. His body was later found near the summit. For even the most capable climber, a prolonged period of time spent in the death zone diminishes cognitive abilities and executive functioning. Actively deteriorating bodily functions prevent a descent to safety. For example, cognitive abilities may worsen until the climber succumbs to a mindset of hopelessness: “I really don’t care if I die or if I just sit down and don’t go any further… I am just getting by” (PBS NOVA). However, while it is impossible for climbers to fully train for the death zone, there are myriads of techniques used by hikers to prevent complications at lower altitudes.

Acclimatization is the idea of spending time at higher altitudes to help physiological adaptation, which is the most effective and safest way to climb. Living at higher altitudes helps the body physiologically adapt to the gradual decrease in oxygen levels. As a result, many journeys to the Mount Everest summit start with hikers spending 10-15 days at towns 3,500 meters above sea level, such as Namche Bazaar, which allows hikers to acclimatize before continuing their ascent up the mountain. During acclimatization, the respiratory, circulatory, renal, and nervous systems become modified to combat lower levels of oxygen. These bodily changes specifically fight the various systems that could be affected by acute mountain sickness (AMS), an umbrella disease. Many short-term effects of AMS occur when the body cannot physically compensate for hyperventilation or vasoconstriction and ultimately leads to conditions like respiratory alkalosis and high-altitude pulmonary edema. Longer-term effects include diseases like polycythemia, which occurs when there is an excess of red blood cells (RBCs) in the body. 

Respiratory alkalosis is the result of irregular breathing at high altitudes. Hyperventilation is the immediate response to low barometric pressures of oxygen, by accelerating breathing when the equilibrium of bicarbonate buffer in the blood is disrupted. Typically, the body utilizes carbon dioxide and water to create acid and bicarbonate to maintain an acidic pH in the body. When the body starts breathing rapidly, a larger-than-normal amount of carbon dioxide is exhaled. This leads to a chemical imbalance that increases the amount of bicarbonate in the body, making the pH more basic. As a result, hyperventilation effects are observed in two ways: a decrease in bodily carbon dioxide and an increased filtering out of bicarbonate by the kidneys to bring down the blood’s pH. Rapid breathing starts when chemoreceptors in the heart are triggered by a condition called hypoxia where there are lower levels of oxygen in the blood. Cranial nerves then relay signals about the low oxygen levels to various areas in the brainstem. From the brainstem, signals will then be sent to quicken the rate of diaphragm contractions, also known as increased ventilation rate. Aggressively stimulating the diaphragm helps the body to temporarily compensate. However, bicarbonate still builds up and may lead to conditions like respiratory alkalosis, in which the body is unable to control breathing. Therefore, decreasing carbon dioxide levels to maintain sufficient oxygen for survival is one of the many ways to acclimate to higher altitudes. In fact, by doing so, climbers can survive in environments where carbon dioxide levels are up to 80% less than typical due to their kidneys becoming trained to filter out bicarbonate more efficiently.

Alongside hyperventilation, the lungs also respond to low levels of oxygen by vasoconstricting, the narrowing of the blood vessels in the lungs. Blood flow will be diverted away from the constricted blood vessel and seek the most trouble-free route to reach an organ. As a result, the constriction of blood vessels will create an imbalance in perfusion levels (the blood available to an organ). With increased blood flow into the lungs, greater pressure is applied to vessels carrying the blood. The presence of excess fluid creates the potential for leakage into other areas of the lung, like the alveoli, and interference with the function of gas exchange. These conditions lead to High Altitude Pulmonary Edema (HACE). More severe cases of HACE can turn into High Altitude Pulmonary Hypertension (HAPH). The effects of HAPH are permanent as there is remodeling of the arteries by an invasion of foreign cells into the poorly oxygenated arteries. Build-up of these foreign cells removes the blood vessels’ elasticity, which makes the pumping of blood more physically taxing. Similar to hyperventilation, vasoconstriction is a compensatory mechanism that can lead to permanent remodeling of a person’s vasculature, if not corrected.

Another way that high altitude can alter blood flow is through an increase in the concentration of red blood cells. Low oxygen levels trigger the release of hypoxia transcription factors like HIF1alpha, HIF2alpha, and HIF3A. While the factors vary in their purpose, the overall goal is to instill proper physiological conditions. These factors bind and upregulate hundreds of genes which create proteins like erythropoietin that are important in amplifying the signal of low oxygen levels. With the upregulation of erythropoietin, the kidneys work to increase the concentration of red blood cells in the body. Erythropoietin stimulates RBC production and leads to a subsequent increase in O2 carrying capacity to compensate for impaired O2 delivery. Increasing RBCs is one of the initial mechanisms used by the body to combat hypoxia. However, larger increases in RBCs and hemoglobin can lead to thicker blood viscosity, subsequently interfering with the flow of blood for lengthy periods of time, as RBCs generally live for 120 days. Alongside the higher production of erythropoietin, there is also escalated production of the molecule 2,3 BPG. The importance of 2,3 BPG lies in the fact that it decreases oxygen’s affinity for hemoglobin, which allows for greater levels of oxygen to diffuse into the tissue and prevent cell death. Erythropoietin is one of the many proteins that are upregulated by hypoxia-induced factors. However, similar to many of the adjustments facilitated in high altitude conditions, an overcorrection can be dangerous. Hikers run the risk of polycythemia, the thickening of the blood to a point where it is unable to travel throughout the body properly. 

While AMS affects many body systems, there is little clinical evidence that implicates it in cases of impaired judgment or psychosis felt by mountaineers. In the DSM-5, psychosis is described as hallucinations, delusions, abnormal psychomotor behavior, etc. Hallucinations are by far the most common symptom of high-altitude psychosis and often appear at 23,000 feet and above. Much of what we know about the impaired judgment of mountaineers have come from first-hand accounts. A common example of psychosis is described as the third man factor. This phenomenon was described in detail by British explorer Frank Smythe as a “strong feeling that I was accompanied by a second person. The feeling was so strong that it completely eliminated all loneliness I might otherwise have felt” (Smythe). There are also detrimental examples of the third man factor. French climber Elisabeth Revol reportedly removed her boot and suffered severe frostbite as she felt the hallucinatory presence of a friendly woman who offered her hot tea and requested that she take off her boot in return. Psychosis is known to disappear as quickly as it appears. With the nature of high altitude psychosis being so mysterious, there is a lack of clinical studies to provide plausible explanations. Head of Emergency Mountain Medicine, Dr. Hermann Brugger, shares that “these hallucinations can’t be linked to easily explainable causes like brain swelling, fluid loss or infection” (MacMillan). Many pilot studies use novel research methods such as self-administered high altitude psychosis (HAPSY) questionnaires to detect whether climbers experienced symptoms of psychosis. This survey contained extremely basic and easy-to-answer statements like, “You have a conversation with a person who is not really there.” However, this survey only points to whether or not a climber has psychotic symptoms and nothing about their origins. There is also research being conducted with mouse models to understand the effects of hypoxia on the brain. Findings show that hypoxia increases neurotransmitters like serotonin that have been linked to hallucinations in schizophrenia. Since the study of high-altitude psychosis is a fledgling field, hikers need to be aware of its potential threat.

Climbing and summiting Mount Everest is a testament not only of human will and determination, but is also a mark of the simultaneous resilience and fragility of the human body. By researching AMS, researchers can better understand how the body adapts to, compensates for, and overcomes extreme conditions, such as hypoxic environments. The future of high altitude studies involve utilizing the benefits of bodily changes at non-sea level altitudes. For example, RBCs’ increased capacity to carry oxygen is now used by athletes and military personnel alike. Scientists are also interested in studying systematic hypoxia experienced by high-altitude populations that produce inflammatory markers similar to those who experienced COVID-19. Understanding how the lungs adapt to depleted oxygen levels may even lead to new treatments for respiratory illness. The study of high-altitude experiences broadens our horizons on the limits of human survival in environments previously thought to be uninhabitable.