Check out these altitude safety tips and facts about common variations of altitude sickness from Summit Expeditions & Nomadic Experience
Life as we know it is completely dependent on oxygen. Humans require a constant supply of it. Generalized hypoxia is the condition in which a body is deprived of adequate oxygen supply. If deprived for six minutes, irreparable damage to the brain can occur.
Contrary to what many believe, air is not sucked into the lungs but rather it is pushed into the lungs by atmospheric pressure. As altitude increases, barometric pressure decreases and therefore less oxygen is pushed into the lungs. Other physiological changes that naturally occur at altitude include increased heart rate, increased respiratory rate, increased metabolic rate, and sometimes an increase in blood pressure.
Hemoglobin is a protein that is carried by red cells. It picks up oxygen in the lungs and delivers it to the cells throughout the body. Typically when breathing at sea level, 96 to 98 percent of hemoglobin molecules in the blood are saturated with oxygen. As altitude increases, blood is less fully saturated and may have as little as 75 percent of what it can carry. Thus, hypoxia occurs in healthy people when they ascend to high altitude, where it can cause acute mountain sickness (AMS), commonly known as altitude sickness.
Acute Mountain Sickness (AMS)
The symptoms of generalized hypoxia depend on its severity and acceleration of onset. In the case of AMS, where hypoxia develops gradually, the symptoms may include headaches, fatigue, shortness of breath, a feeling of euphoria, or nausea.
The impact of altitude on the body is determined by the priority the body places on oxygen supply to each organ system. The brain receives 15 percent of the blood pumped by the heart and uses over 20 percent of all oxygen consumed; the cerebral cortex is the most demanding. Therefore, generalized hypoxia affects judgment and high intellectual functions early. The research is unclear as to why headaches occur at altitude but this is one common sign of AMS. Other symptoms, such as nausea, vomiting, and disrupted sleep may be due to swelling or altered blood flow to the mid-brain where the centers that control these functions are located.
Four key factors usually determine whether a person will experience symptoms of AMS at elevation: (1) speed of ascent; (2) altitude reached; (3) health status (factors such as malnutrition, dehydration, fatigue, and any of several illnesses will increase risk); and (4) individual characteristics (genetic influences or some unusual metabolic or circulatory variant may affect susceptibility).
High Altitude Pulmonary Edema (HAPE)
Although less common, HAPE is more serious than AMS.
With an increase in altitude, fluid develops in the lung tissue that separates air sacs, alveoli, from capillaries. Typically this is promptly reabsorbed. If it is not and accumulates in the alveoli, movement of oxygen from the lungs to the blood is impaired and more fluid accumulates in the air sacs.
Symptoms of HAPE include shortness of breath even at rest and an irritative cough that may produce a frothy, often blood-tinged sputum. Mental confusion, extreme fatigue, and a struggling drunken walk may follow soon; the climber will slip into coma unless treated promptly.
High Altitude Cerebral Edema (HACE)
HACE, although extremely rare, can be fatal with little to no warning. It is believed to be due to parts of the brain being waterlogged. One early sign of HACE is difficulty in walking (also seen in HAPE) and with finger and hand motions.
Altitude Safety Tips for Staying Well at Altitude
- Eat regular nutritious meals
- Drink lots of fluids
- Gain altitude slowly (acclimatize)
- Inform your guide of any signs or symptoms you experience – even if only minor
- Keep a smile on your face
Source: Houston C. “High Altitude Illness and Wellness” ICS Books, Indiana, 1993.