Like most, I woke up this morning and had a cup of coffee, attained some level of consciousness, and then got dressed. But what to wear? I didn’t think terribly much about it on this particular day. But upon stepping outside, I was made acutely aware, once again, it’s winter in the UP.

It takes a hardy soul to endure these climes, at least from a psychological perspective. What about physically? Are some people just tougher than others, able to withstand frigid temps for days on end? On the contrary, there are many biologic constraints to the human body’s ability to exist in sub-arctic temps. Depending on a large number of variables such as elevation, humidity, wind speed, and more, exposure to lower temperatures will invariably cause certain physical changes, most of them harmful.

The term for the pathologic changes which occur to the body with cold exposure is hypothermia. When someone has this, their core body temperature will be lowered. Statistically, this usually occurs in an austere or wilderness environment. How much lower core temp goes determines the severity of the repercussions of hypothermia. Mild hypothermia is defined as a core temperature between 32 degrees and 35 degrees Centigrade. The physiologic effects are slight, such as shivering to generate heat and an increased metabolic rate. Heart rate will rise, as will cardiac output. Consciousness is not affected; the afflicted will be awake and shivering. When only mild hypothermia has developed, returning to normal temps is the primary treatment required.

Let us consider those body parts most over-exposed, the farthest away, our limbs. I’m talking about those very important arms and legs. Everyone has heard the term frostbite. How about frostnip? This term is not so commonplace but actually occurs quite frequently. In this situation, the skin will become cold, numb and white. A tingling sensation is often experienced, most commonly in the fingers, nose, ears and toes. Frostnip, which often affects people who live or work in cold climates, doesn’t permanently damage the skin and can be treated with simple first-aid measures.

With superficial frostbite, the affected skin will feel warm, a sign of more serious involvement. If you have suffered this degree of frostbite, fluid-filled blisters will appear after rewarming the skin, generally a day or so later. With deep frostbite, numbness will be noted. Joints or muscles may no longer work. Large blisters will form a day or two after rewarming. Later, the skin and deeper tissues in the affected area turns black and hard. As you may have surmised, this is gangrene in which there is tissue death.

The actual nature of frostbite, the specific mechanism, has been controversial. Most authorities believed it was a direct thermal injury. Others believed the tissue injury was indirect, resulting from changes to the microcirculation. Now it appears that both are important. Cold can destroy tissue directly by forming ice crystals, but also by producing changes to the blood vessels. The result is that fingertips or toes become pale, then “dusky”, a sort of purple-grey color. In time, the most severely affected areas can turn black. How deep this tissue death extends won’t be known for weeks. This is why amputation should be delayed for weeks if not months: the amount of tissue lost may turn out to be much less than anticipated.

Although still taught, gradual re-warming is not the optimal treatment. This has been conclusively proven. Rapid re-warming will lead to significantly less tissue destruction. This is best achieved with the use of a tub of water, maintained at a temperature of between 103 and 107 degrees by the occasional addition of hot water. Soaking the affected part in hotter temps risks further tissue injury while a lower temperature bath will not have the desired effect. After a few days of immobilization, some gentle range of motion exercises should be started.

As to the systemic effects of worsening cold weather exposure, aka moderate hypothermia, the body’s core temperature will reach somewhere in the 28-32°C range. Shivering ceases and heat production falls. Moreover, metabolic processes slow, and certain characteristic ECG changes of hypothermia begin to be seen. Patients with moderate hypothermia will require active rewarming because they are not producing heat. This means heat will need to be provided in some form to ensure recovery.

Hypothermia of sufficient duration and intensity will have dramatic effects on many physiologic processes and many organ systems. One of particular concern is the cardiovascular system. Hypothermia decreases the functioning of the cells that control heart rate, initially leading to an abnormally slow heartbeat. Rewarming is required in order to restore normal electrophysiologic function. As the effects of hypothermia progress, characteristic ECG changes will be seen. This slower rate may progress to atrial fibrillation, and can ultimately lead to no heartbeat whatsoever.

The functioning of the central nervous system decreases linearly with temperature. The consequence of this decrease is that, at temperatures below 33°C, cerebral metabolism is markedly reduced. Consequently, the afflicted may manifest confusion, which can progress to delirium, even coma. The decrease in brain function may actually be protective. There have been many reports of patients with severe hypothermia who make a complete recovery as far as brain function.

To survive and thrive in our meteorological environment (at least until climate change alters things), one must prepare appropriately. Temperatures below zero demand some thought be given to your wardrobe choices. The key word here is “preparation”, dress in layers, heat-retaining materials, with face and extremity protection. With the right kind of equipment, it is certainly possible to safely survive, even thrive, in these arctic conditions. But we are all human, which means we make mistakes. Don’t let poor clothing choices lead to pain, suffering, possibly even disability. We are all human, which means anyone of us can suffer from frostbite and/or hypothermia. These can be dangerous times; dress smart, play safe!

Editor’s note: Dr. Conway McLean is a physician practicing foot and ankle medicine in the Upper Peninsula, with a move of his Marquette office to the downtown area. McLean has lectured internationally on wound care and surgery, being double board certified in surgery, and also in wound care. He has a sub-specialty in foot-ankle orthotics. Dr. McLean welcomes questions or comments atdrcmclean@outlook.com.