High Altitude Climbing

High altitude climbing is a very dangerous sport, well, we won't call it a sport, it is more like a profession for highly skilled individuals. High altitude climbing is when mountain climbers decide that they want to climb higher and more difficult mountains. To do this they need the right training and also need to know the effects of high altitude climbing to their bodies.

The body attempts to maintain a state of homeostasis or balance to ensure the optimal operating environment for its complex chemical systems. Any change from this homeostasis is a change away from the best possible operating environment. The body attempts to correct this imbalance. One such imbalance is the effect of increasing altitude on the body's ability to provide adequate oxygen to be utilized in cellular respiration. With an increase in elevation, a typical occurrence when climbing mountains, the body is forced to respond in various ways to the changes in external environment. Foremost of these changes is the diminished ability to obtain oxygen from the atmosphere. If the adaptive responses to this stressor are inadequate the performance of body systems may decline dramatically. If prolonged the results can be serious or even fatal.

In looking at the effect of altitude on body functioning we first must understand what occurs in the external environment at higher elevations and then observe the important changes that occur in the internal environment of the body in response. In discussing altitude change and its effect on the body mountaineers generally define altitude according to the scale of high (8,000 - 12,000 feet), very high (12,000 - 18,000 feet), and extremely high (18,000+ feet), (Hubble, 1995).

A common misperception of the change in external environment with increased altitude is that there is decreased oxygen. This is not correct as the concentration of oxygen at sea level is about 21% and stays relatively unchanged until over 50,000 feet (Johnson, 1988). What is really happening is that the atmospheric pressure is decreasing and subsequently the amount of oxygen available in a single breath of air is significantly less. At sea level the barometric pressure averages 760 mmHg while at 12,000 feet it is only 483 mmHg. This decrease in total atmospheric pressure means that there are 40% fewer oxygen molecules per breath at this altitude compared to sea level (Princeton, 1995). The pulmonary surface and the thickness of the alveolar membranes are not directly affected by a change in altitude. It is this inadequate supply of oxygen that results in difficulties for the body at higher elevations.

A lack of sufficient oxygen in the cells is called anoxia. Sometimes the term hypoxia, meaning less oxygen, is used to indicate an oxygen debt. While anoxia literally means no oxygen it is often used interchangeably with hypoxia. There are different types of anoxia based on the cause of the oxygen deficiency. Anoxic anoxia refers to defective oxygenation of the blood in the lungs. This is the type of oxygen deficiency that is of concern when ascending to greater altitudes with a subsequent decreased partial pressure of O2. Other types of oxygen deficiencies include: anemic anoxia (failure of the blood to transport adequate quantities of oxygen), stagnant anoxia (the slowing of the circulatory system), and histotoxic anoxia (the failure of respiratory enzymes to adequately function). Anoxia can occur temporarily during normal respiratory system regulation of changing cellular needs. An example of this would be climbing a flight of stairs. The increased oxygen demand of the cells in providing the mechanical energy required to climb ultimately produces a local hypoxia in the muscle cell. The first noticeable response to this external stress is usually an increase in breathing rate. This is called increased alveolar ventilation.

The question involved with altitude changes becomes what happens when the normal responses can no longer meet the oxygen demand from the cells? One possibility is that Acute Mountain Sickness (AMS) may occur. AMS is common at high altitudes. At elevations over 10,000 feet, 75% of people will have mild symptoms (Princeton, 1995). The occurrence of AMS is dependent upon the elevation, the rate of ascent to that elevation, and individual susceptibility. Acute Mountain Sickness is labeled as mild, moderate, or severe dependent on the presenting symptoms. Many people will experience mild AMS during the process of acclimatization to a higher altitude. In this case symptoms of AMS would usually start 12-24 hours after arrival at a higher altitude and begin to decrease in severity about the third day. The symptoms of mild AMS are headache, dizziness, fatigue, shortness of breath, loss of appetite, nausea, disturbed sleep, and a general feeling of malaise (Princeton, 1995). These symptoms tend to increase at night when respiration is slowed during sleep. Mild AMS does not interfere with normal activity and symptoms generally subside spontaneously as the body acclimatizes to the higher elevation. Moderate AMS includes a severe headache that is not relieved by medication, nausea and vomiting, increasing weakness and fatigue, shortness of breath, and decreased coordination called ataxia (Princeton, 1995). Normal activity becomes difficult at this stage of AMS, although the person may still be able to walk on their own. A test for moderate AMS is to have the individual attempt to walk a straight line heel to toe. The person with ataxia will be unable to walk a straight line. If ataxia is indicated it is a clear sign that immediate descent is required. In the case of hiking or climbing it is important to get the affected individual to descend before the ataxia reaches the point where they can no longer walk on their own. Severe AMS presents all of the symptoms of mild and moderate AMS at an increased level of severity. In addition there is a marked shortness of breath at rest, the inability to walk, a decreasing mental clarity, and a potentially dangerous fluid buildup in the lungs.

There is really no cure for Acute Mountain Sickness other than acclimatization or descent to a lower altitude. Acclimatization is the process, over time, where the body adapts to the decrease in partial pressure of oxygen molecules at a higher altitude. The major cause of altitude illnesses is a rapid increase in elevation without an appropriate acclimatization period. The process of acclimatization generally takes 1-3 days at the new altitude. Acclimatization involves several changes in the structure and function of the body. Some of these changes happen immediately in response to reduced levels of oxygen while others are a slower adaptation. Some of the most significant changes are: Chemoreceptor mechanism increases the depth of alveolar ventilation. This allows for an increase in ventilation of about 60% (Guyton, 1969). This is an immediate