The Effects Of Altitude On Human Physiology Changes In Altitude Have A Profound Effect On The Human Body The Body Attempts To

.. taneously 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. ACCLIMATIZATION There is really no cure for Acute Mountain Sickness other than acclimatization or descent to a lower altitude.

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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 response to oxygen debt. Over a period of several weeks the capacity to increase alveolar ventilation may increase 600-700%. Pressure in pulmonary arteries is increased, forcing blood into portions of the lung which are normally not used during sea level breathing. The body produces more red blood cells in the bone marrow to carry oxygen.

This process may take several weeks. Persons who live at high altitude often have red blood cell counts 50% greater than normal. The body produces more of the enzyme 2,3-biphosphoglycerate that facilitates the release of oxygen from hemoglobin to the body tissues (Tortora, 1993). The acclimatization process is slowed by dehydration, over-exertion, alcohol and other depressant drug consumption. Longer term changes may include an increase in the size of the alveoli, and decrease in the thickness of the alveoli membranes. Both of these changes allow for more gas transfer.

TREATMENT FOR AMS The symptoms of mild AMS can be treated with pain medications for headache. Some physicians recommend the medication Diamox (Acetazolamide). Both Diamox and headache medication appear to reduce the severity of symptoms, but do not cure the underlying problem of oxygen debt. Diamox, however, may allow the individual to metabolize more oxygen by breathing faster. This is especially helpful at night when respiratory drive is decreased. Since it takes a while for Diamox to have an effect, it is advisable to start taking it 24 hours before going to altitude.

The recommendation of the Himalayan Rescue Association Medical Clinic is 125 mg. twice a day. The standard dose has been 250 mg., but their research shows no difference with the lower dose (Princeton, 1995). Possible side effects include tingling of the lips and finger tips, blurring of vision, and alteration of taste. These side effects may be reduced with the 125 mg.

dose. Side effects subside when the drug is stopped. Diamox is a sulfonamide drug, so people who are allergic to sulfa drugs such as penicillin should not take Diamox. Diamox has also been known to cause severe allergic reactions to people with no previous history of Diamox or sulfa allergies. A trial course of the drug is usually conducted before going to a remote location where a severe allergic reaction could prove difficult to treat.

Some recent data suggests that the medication Dexamethasone may have some effect in reducing the risk of mountain sickness when used in combination with Diamox (University of Iowa, 1995). Moderate AMS requires advanced medications or immediate descent to reverse the problem. Descending even a few hundred feet may help and definite improvement will be seen in descents of 1,000-2,000 feet. Twenty-four hours at the lower altitude will result in significant improvements. The person should remain at lower altitude until symptoms have subsided (up to 3 days). At this point, the person has become acclimatized to that altitude and can begin ascending again.

Severe AMS requires immediate descent to lower altitudes (2,000 – 4,000 feet). Supplemental oxygen may be helpful in reducing the effects of altitude sicknesses but does not overcome all the difficulties that may result from the lowered barometric pressure. GAMOW BAG This invention has revolutionized field treatment of high altitude illnesses. The Gamow bag is basically a portable sealed chamber with a pump. The principle of operation is identical to the hyperbaric chambers used in deep sea diving. The person is placed inside the bag and it is inflated.

Pumping the bag full of air effectively increases the concentration of oxygen molecules and therefore simulates a descent to lower altitude. In as little as 10 minutes the bag creates an atmosphere that corresponds to that at 3,000 – 5,000 feet lower. After 1-2 hours in the bag, the person’s body chemistry will have reset to the lower altitude. This lasts for up to 12 hours outside of the bag which should be enough time to travel to a lower altitude and allow for further acclimatization. The bag and pump weigh about 14 pounds and are now carried on most major high altitude expeditions.

The gamow bag is particularly important where the possibility of immediate descent is not feasible. OTHER ALTITUDE-INDUCED ILLNESS There are two other severe forms of altitude illness. Both of these happen less frequently, especially to those who are properly acclimatized. When they do occur, it is usually the result of an increase in elevation that is too rapid for the body to adjust properly. For reasons not entirely understood, the lack of oxygen and reduced pressure often results in leakage of fluid through the capillary walls into either the lungs or the brain. Continuing to higher altitudes without proper acclimatization can lead to potentially serious, even life-threatening illnesses.

HIGH ALTITUDE PULMONARY EDEMA (HAPE) High altitude pulmonary edema results from fluid buildup in the lungs. The fluid in the lungs interferes with effective oxygen exchange. As the condition becomes more severe, the level of oxygen in the bloodstream decreases, and this can lead to cyanosis, impaired cerebral function, and death. Symptoms include shortness of breath even at rest, tightness in the chest, marked fatigue, a feeling of impending suffocation at night, weakness, and a persistent productive cough bringing up white, watery, or frothy fluid (University of Iowa, 1995.). Confusion, and irrational behavior are signs that insufficient oxygen is reaching the brain. One of the methods for testing for HAPE is to check recovery time after exertion.

Recovery time refers to the time after exertion that it takes for heart rate and respiration to return to near normal. An increase in this time may mean fluid is building up in the lungs. If a case of HAPE is suspected an immediate descent is a necessary life-saving measure (2,000 – 4,000 feet). Anyone suffering from HAPE must be evacuated to a medical facility for proper follow-up treatment. Early data suggests that nifedipine may have a protective effect against high altitude pulmonary edema (University of Iowa, 1995).

HIGH ALTITUDE CEREBRAL EDEMA (HACE) High altitude cerebral edema results from the swelling of brain tissue from fluid leakage. Symptoms can include headache, loss of coordination (ataxia), weakness, and decreasing levels of consciousness including, disorientation, loss of memory, hallucinations, psychotic behavior, and coma. It generally occurs after a week or more at high altitude. Severe instances can lead to death if not treated quickly. Immediate descent is a necessary life-saving measure (2,000 – 4,000 feet). Anyone suffering from HACE must be evacuated to a medical facility for proper follow-up treatment.

CONCLUSION The importance of oxygen to the functioning of the human body is critical. Thus the effect of decreased partial pressure of oxygen at higher altitudes can be pronounced. Each individual adapts at a different speed to exposure to altitude and it is hard to know who may be affected by altitude sickness. There are no specific factors such as age, sex, or physical condition that correlate with susceptibility to altitude sickness. Most people can go up to 8,000 feet with minimal effect.

Acclimatization is often accompanied by fluid loss, so the ingestion of large amounts of fluid to remain properly hydrated is important (at least 3-4 quarts per day). Urine output should be copious and clear. From the available studies on the effect of altitude on the human body it would appear apparent that it is important to recognize symptoms early and take corrective measures. Light activity during the day is better than sleeping because respiration decreases during sleep, exacerbating the symptoms. The avoidance of tobacco, alcohol, and other depressant drugs including, barbiturates, tranquilizers, and sleeping pills is important. These depressants further decrease the respiratory drive during sleep resulting in a worsening of the symptoms. A high carbohydrate diet (more than 70% of your calories from carbohydrates) while at altitude also appears to facilitate recovery.

A little planning and awareness can greatly decrease the chances of altitude sickness. Recognizing early symptoms can result in the avoidance of more serious consequences of altitude sickness. The human body is a complex biochemical organism that requires an adequate supply of oxygen to function. The ability of this organism to adjust to a wide range of conditions is a testament to its survivability. The decreased partial pressure of oxygen with increasing altitude is one of these adaptations. Sources: Electric Differential Multimedia Lab, Travel Precautions and Advice, University of Iowa Medical College, 1995.

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