How Your Body Uses Food for Thermoregulation, By Joshua English EMT-P

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Regulation of body temperature in the winter months can be challenging. Add in factors experienced on a mountain hunt, and thermoregulation can be particularly challenging. Long hours of glassing on a mountainside can easily lead to hypothermia if caution is not taken.

Physiology

Your body can maintain a core temperature of approximately 99F (37C) even in extreme conditions. The hypothalamus is chiefly responsible for involuntary responses to cold (i.e. – shivering). Your body also vasoconstricts peripheral vessels (especially in the skin) in an attempt to reduce the amount of heat lost through radiation. By shunting blood to the core, the body is able to further maintain adequate temperatures. This vasoconstriction comes at a cost, however, and the major effect we can all relate to is cold hands, feet and faces. These responses to cold can also cause our brains to “suggest” to the body to move around or fidget in order to generate heat through metabolic means achieved through skeletal muscle movement. It is also known that your body increases its metabolic rate in order to generate heat at the cellular level (remember this for later).

Environmental Factors

There are several ways that the body loses heat to the environment:

  1. Radiation
  2. Conduction
  3. Evaporation

We wear ultra-high-tech clothing to counteract these factors, and we make sure that we have super warm glassing gloves to avoid non-functioning hands when the shot of a lifetime comes. If you’re smart, you make sure that you have properly fitted boots that do not cut off blood flow to the feet which reduces the amount of warm, circulating blood to the feet. You should also make sure that you do not sit directly on cold rock and use your inflatable sleeping pad to prevent loss of heat through conduction. During your hike up the mountain, shedding layers to prevent sweating can help reduce heat loss through evaporation. But did you ever consider that your caloric intake could help you avoid hypothermia?

Increased Metabolism

Remember that increased metabolic rate I mentioned above? That increase in metabolism is through a process called cellular respiration. Increased metabolism means you can eat more calories without gaining weight, because your body is using those calories to turn up the heat in your core. Staying well fed during cold exposure can also reduce the amount of vasoconstriction necessary to maintain proper core temperature. Eating high-energy snacks during glassing or other down times on the mountain is essential to helping your body continually churn and burn.

The calorie is effectively a unit of measurement for heat. It is the measurement of how much energy is needed to raise the temperature of one kilogram of water by one degree Celsius. If your normal caloric intake per day is around 2500-3000 calories, consider adding about 500-800 more calories when there is the potential for cold weather. High calorie bars can be a great source for these extra calories without adding a bunch of food weight. If your stomach can’t handle these types of bars, maybe you aren’t drinking enough water when eating them. Avoid making a gut brick, and drink plenty of fluids. Fluids are important anyway, as you lose a lot of water vapor in your breath (which also reduces your internal temperature). People often forget to hydrate in cold weather, but it is doubly important when temperatures drop due to increases in loss of heat due to evaporation.

During your hike, don’t be a speed demon. Hike efficiently and if possible use a heart rate monitor to make sure you are not overexerting yourself. Overexertion, like having a heavy gas pedal, can cause you to burn fuel faster. Finding that balance between reducing pack weight and hiking efficiently can help conserve valuable calories during your hunt. It’s strange to think about, but lightweight backpacking has additional benefits beyond increased comfort. It actually can help with thermoregulation through lower exertion levels.

Your internal engine needs to be topped off in order to keep warm. Make sure you are eating enough to stay in the hunt. Eating right is only one factor in battling the cold, but it is an often overlooked one. There were some interesting studies conducted in the 1940’s that showed that lab rats ate more when temperatures dropped while still maintaining body weight. When you’re in the mountains and your stomach starts to talk to you, your body is asking you to stoke the fire. Don’t ignore this. Better yet, have a plan for caloric intake so you don’t get behind the 8-ball when the mercury drops.

Thermoregulation

Recognition and Treatment of Cold Related Injuries and Illnesses

Despite our best efforts to prepare for the worst, Mother Nature is hell bent on making our outdoor experiences a pure suffer-fest. Even if you eat right and plan your gear accordingly, there are myriad ways that you can still find yourself, or someone in your hunting party, facing the effects of cold related injuries and illnesses. Both hypothermia and frostbite can be life threatening if left unchecked. Both entities are best handled in the early stages, so early detection is the best way to prevent poor outcomes.

Frostbite

This entity has plagued mountaineers since the dawn of man. One of the main culprits of frostbite in a mountain setting is ill fitting boots. Boots that are too tight, reduce circulation to the foot. Circulation keeps warm blood flowing to the extremities, so a reduction in blood flow can result in rapid cooling of the affected limb, especially in extreme conditions. Your feet can be bone dry, in a pair of $600 mountain boots, with the world’s most technical socks money can buy, but tie up those Scarpas too tight, and you’ll be cruising for a world of hurt when your feet start to slowly freeze at the cellular level. If your feet start to feel cold in your boots, don’t ignore them. Try and figure out the root cause and fix it. Frostbite can lead to amputation or worse, death if exposure continues.

Another bad actor in frostbite is exposed skin of the face and hands. Having a way to cover your ears, mouth, and nose is vital to ensuring you don’t end up looking like one of the Jacksons after a bad nose-job! A great glove system is also important. It is not enough to have one pair of gloves (one is none, two is one). Sweaty hands can chill down very quickly, so layering your gloves will allow you to adjust your warmth so you can prevent sweat from leading to evaporative heat loss.

As the skin starts to freeze, it will turn red and feel cold to the touch. An ominous sign is skin that has blanched (or turned ashen white), become fully numb, and is hard. As frostbite worsens, the skin can blister. These blisters can easily become infected and gangrene can set in, which can be deadly. Because of the potential for a very negative outcome, frostbite should be considered an evacuation event (unless caught very early and there is a remedy to keep it from re-occurring).

To care for a frostbitten body part, take care to not rewarm the part with too much heat. Because the body part is often numb, it is difficult for the injured person to know when their skin is burning. Wrap the affected part in a warm sleeping bag or clothing, this passive warming method is safe, but less effective in extreme conditions. Immersion in warm water (between 40 and 42 degrees Celsius) is faster but trickier to manage in austere environments. Your proximity to an evacuation site will best determine what method you use.

NOTE: Only rewarm the body part if you are certain that it will not refreeze. It is best to walk out on a cold stump of a foot than to rewarm it only to have it re-freeze during the hike out. The damage caused by thawing and refreezing can almost certainly ensure that some part of the affected limb will be amputated.

Avoid rewarming by a fire for the above mentioned reason. As well, vigorous rubbing of a frostbitten limb can cause tissue damage as well. As the affected body part rewarms, a rotten feeling of “pins and needles” can be felt along with abject pain. But please don’t underestimate the potential for damage caused by thawing and refreezing! Consuming alcohol or tobacco products constricts blood flow to the extremities and can hasten the onset of frostbite, so act accordingly.

Thermoregulation

Hypothermia

When the body loses heat faster than it can produce it, the core body temperature begins to plummet, causing your body’s major organs to function improperly. As mentioned above, your body responds to cooling by shivering. This shivering burns fuel, and causes muscle movement that is intended to warm the body’s core temperature. Shivering is a very early sign, and should not be ignored if encountered. Certain conditions can hasten hypothermia, but one that we can easily control is dehydration and low caloric intake.

Mild Hypothermia can cause:

  • Shivering
  • Confusion
  • Slurred speech
  • Increased heart and respiratory rate
  • Nausea

Since hypothermia affects our mental status, it is important to take notice of a hunting partner who becomes more annoying than usual, or who has an unexplained change in demeanor. The most annoying person on the hunt may be innocently experiencing mild hypothermia, so don’t ask them to go out alone to glass on the opposite ridge. Instead check in with them to make sure they are warm enough, have eaten plenty of calories, and are not dehydrated. If you hunt solo, you should pay attention to your own mental status. If your mind wanders a little too easily, and you are feeling cold, take that as a sign that your body is losing the thermoregulation battle and take evasive action. Shivering is easy to spot, but changes in mentation are a little more subtle. Picking up on the subtle changes in mentation can be the difference in early recognition of hypothermia.

As hypothermia progresses to moderate and severe:

  • Shivering can stop
  • A person can seem aloof to their worsening condition
  • Decision making is severely impaired and people do very stupid things like shed warm clothing
  • Incoherent speech and drowsiness are ominous signs as well as a marked decrease in consciousness
  • The pulse will weaken and breathing slows down

When we get to this point, we have a very true emergency on our hands and we need to act fast to get this person warmed up again. Evacuation is key, but it is important to reverse the effects of hypothermia. Do not use direct heating, since rapidly reheating the hypothermic patient can cause irregular heart rhythms. Wrap the person in warm sleeping bags. Skin to skin contact under sleeping bags can be very effective, so get over yourself and snuggle right up to your buddy…it’ll save his life. Since the body can lose heat through conduction (direct contact with a cold object) make sure to insulate the person from the cold ground. If at all possible, get the person out of the exposed, cold air. A tent can do well to protect from further heat loss due to convection. If the person is fully awake, and can hold their own head up, give them warm liquids to drink as this is very effective at warming them from the inside out. Adding some chocolate powder or soup broth will replenish energy lost through shivering as well. Pull out all the stops to get the person back to a warmer state, but remember to avoid direct heat sources. If the person has on wet clothing, be sure to remove the wet clothing, especially before heading back out on the trail. The wet clothing will cause rapid heat loss through the evaporative effect.

If caught early, hypothermia is a nuisance. If measures can be taken to prevent another episode, use your best judgment. Erring on the side of caution and making a plan for exfil after rewarming is probably the best plan. Once someone experiences hypothermia, the only way to truly avoid further complications is to remove that person from the environment that caused it in the first place. A warm truck is a great way to stabilize the person’s thermoregulator so they can live to hunt another day. If moderate to severe hypothermia sets in, consider air evacuation. Extracting a hypothermic patient from a mountainside can be very difficult as they would be of no help during the extraction. Always have a doomsday plan in place that includes a way to contact rescue teams that can arrange for an airlift if necessary. I always reiterate the notion that failing to plan is planning to fail when teaching wilderness medicine.

Pay attention to the early signs of hypothermia, and it will keep you and your hunting partners in the hunt…better yet, plan well, eat well, and stay hydrated to avoid this dastardly entity in the first damn place!

Be safe out there.

 


 

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