Physiology of Mountaineering

Hydration

Humans are mostly water. Our brain is cushioned by fluid, our joints are lubricated by fluid, our blood is 90% water, and every biochemical reaction takes place in water. Exercise causes water loss through sweating, breathing, and metabolism. When it is warm we sweat to lose heat and when it is cold we lose water to moisten the cold air we breathe. Obviously maintaining enough water in our system is important, but how important?

Dehydration

Dehydration is often overlooked as a cause of accidents, illness, and injury in the mountains. With just a 2% fluid deficit we experience mental deterioration, decreased group cooperation, vague discomfort, lack of energy and appetite, flushed skin, impatience, sleepiness, nausea, an increased pulse rate and a 25% loss in efficiency.

How much water should we drink to stay healthy? Probably more than we usually drink. 3 to 4 liters a day is the minimum, with another liter added for cold or high altitude conditions. Thirst is a poor indicator, alerting us to the fluid deficit after we are already dehydrated and indicating we are satiated before we are fully rehydrated. Urine color and volume are helpful indicators; darker, more concentrated urine is an indicator of dehydration. This is a later sign, appearing after our body has decided to conserve fluid.

Fluids must be forced to maintain hydration in the mountains.

Drink early, anticipating fluid loss throughout the day.
Drink often, preventing mental and physical deterioration.
Drink more than you think you need.

Hypothermia

Hypothermia occurs when body temperature drops to 95° F or lower. It can develop whenever heat loss exceeds heat production and is common during the wind, rain and hail of summer as well as the cold of winter. In order to prevent hypothermia it helps to understand the mechanisms of heat production and heat loss.

Heat Production

Our basal metabolic rate is a constant internal furnace. Shivering produces heat at a rate 5 times greater than our metabolic rate.

How We Lose Heat

Conduction: Direct contact between a hot and cold object.
Convection: Heat loss to moving air or water.
Radiation: Infrared or heat radiation passing to a cold object.
Evaporation: Through sweating and breathing.

Signs & Symptoms

Mental: Apathy, lethargy, slow and improper response to cold, deterioration in decision making ability, increased complaints, decreased group cooperation.

Physical: Shivering, loss of fine motor skills progressing to stumbling, clumsiness and falling.

Treatment & Prevention

Remove yourself from the cold, dry off, insulate, and hydrate with hot drinks and food. With what we know about heat loss, we should never fall victim to hypothermia.

Frostbite

As blood flow declines, cooling can progress to freezing. The fluid between cells freezes forming ice crystals that draw water out of the cells, dehydrating them. A second phase of damage occurs during rewarming. Damaged cells release substances that promote constriction and clotting in small blood vessels, impairing blood flow to the tissues. Frostnip, Superficial frostbite, and Deep frostbite correlate to 1st, 2nd and 3rd degree burns.

Causes of frostbite include

  • cold stress
  • low temperatures
  • wind chill
  • poor insulation
  • contact with supercooled metal or gasoline
  • interference with circulation due to
    • cramped position
    • tight clothing
    • local pressure
    • tight fitting or laced boots
    • dehydration.

Immersion Foot

A local, non-freezing cold injury that occurs in cold, wet conditions usually in temperatures of 30 to 40° F. It can occur with only ten hours of exposure to these conditions. Dry socks and feet provide total protection. Rotate socks as needed. Dry out socks on your body and in your sleeping bag overnight, and always sleep with warm dry feet.

Altitude Illness

Oxygen diffuses from the alveoli in the lungs into the blood because the gas pressure is greater in the alveoli than in blood. At altitude, diminished air pressure reduces the pressure in the alveoli and decreases the amount of oxygen diffusing into the blood.

Factors that can affect the incidence and severity of altitude illness:

  1. Rate of ascent
  2. Altitude attained (especially sleeping altitude)
  3. Length of exposure
  4. Level of exertion
  5. Hydration and diet
  6. Inherent physiological susceptibility

Signs & Symptoms

AMS: headache, malaise, loss of appetite, nausea, disturbed sleep, peripheral edema

Pulmonary Edema (fluid accumulation in the lungs):
AMS, shortness of breath, fatigue, dry cough progressing to productive cough, increased heart rate and respiratory rate, rales (sounds of fluid in the lungs), ataxia.

Cerebral Edema (swelling of the brain):
AMS, changes in level of consciousness, ataxia, severe lassitude, headache, vision disturbances, seizures, hallucinations, etc.

Prevention & Treatment

Ascend slowly, climb high and sleep low, high carbohydrate diet, hydrate. If you experience the symptoms of altitude illness, the most effective treatment is to descend as soon as possible.

The trip was a fantastic experience! We were amazed at the broad range of locations and activities we got to experience in a short time span. Our guide was expert, kind and funny! Overall, we were thrilled with our visit to Iceland!

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