We have heard homeless people, stranded mountaineers or lost hikers die during winter due to prolonged exposure to cold. But what exactly occurs in human body that causes cold to kill a person?
You and I are living because oxygen is being continuously supplied to the cells in the brainstem that controls our respiration and make our heart beat. Life ceases to exist without oxygen. If 4-6 minutes passes without the brainstem cells getting the oxygen they are irreversibly killed, incapacitating them to initiate and regulate the respiration and heart beat and terminating the person inside who they reside.
Whatever reason that commences the ‘Flow Chart of Death’ or ‘Algorithm of Dying’ — gun shot injury, drowning, starvation, dehydration, cancer, hypothermia — the ultimate cause of death is lack of oxygen to the cells in brainstem in the brain that initiates and control respiration.
This is also the ultimate cause of death initiated by hypothermia. Read on to see how.
Humans are warm blooded animals which means they produce their own heat to keep their inside/core temperature between 97 ° – 100° Fahrenheit (° F) or 36.1° – 37.7° Centigrade (°C) unlike cold blooded animals like frogs, snakes and crocodile who adapt to the outside temperature. Their body temperature is cold if the outside temperature is cold and warm if the outside temperature is warm.
Where does the heat come from to maintain out body temperature between 97-100° F? We produce heat on our own by the food we eat. Whatever food we eat, it is broken down or digested into either glucose (unit of carbohydrate), amino acid (unit of protein), and lipid (unit of fat) that enter blood steam. Part of the food we eat is wasted and are excreted via feces or urine.
The digested food enters the blood stream and then into the cells and into cell organelle called mitochondria where they are reacted by oxygen to produce ATP, the energy, carbon dioxide and heat. If human body were a machine then heat would be a waste product that the machine would want to minimize because it consumes the machine’s share of the ‘food’.
This heat produced via food is our inherent source to keep our body warm. Complying with the law of thermodynamics, human body loses heat to the outside if the outside temperature is cooler than the body via conduction, radiation or convention. The cooler the outside temperature than our skin, the faster the heat is lost to the surrounding.
As long as the outside temperature is between 68°F -113°F or 20°C- 45°C, our body has the ability to maintain the body temperature to the normal range around 97° F. Beyond that, our body fails to maintain the core temperature and begins to succumb to the elements and begins to cool or warm to match the temperature of the environment.
With each of the 50-75 trillion human cells producing heat in our body, chances are that our body is overheated in warmer surrounding or may be under heated when body need to match the heat loss in an excessively colder surrounding.
To ensure heat produced by these cells does not exceed the normal body temperature range, the anterior hypothalamic nucleus (AHN), a part of the hypothalamus in the brain takes a number of actions.
Temperature sensors located at various parts in the skin and inside human body send continuous data to AHN. Based on these data, hypothalamus take actions to increase or decrease heat production. If the hypothalamus senses the skin temperature is above 37°C or 98.6°F, it causes skins to produce sweat to evaporate the heat away and/or to lose heat via convention and radiation.
If the skin temperature drops below 37° C or 98.6°F, the AHN initiates a series of responses to minimize heat loss. They include constriction of blood vessels supplying skin to decrease the flow of heat to the skin, shivering to increase heat production in the muscles, secreting hormones from supra-renal gland called epinephrine and Norepinephrine and thyroid gland called Thyroxin to reduce heat loss.
Humans lack the amount of subcutaneous fat that emperor penguins of Antarctica have to keep the core organs warm. Special body features of these penguins such as uniquely structured feather, bloodless tail, and meager supply of blood minimize heat loss. Further, they characteristically huddle in a group during ice storms that frequently occur in Antarctica. Huddling together converse heat and minimize heat loss.
When human body is constantly exposed to an environment cooler than its skin temperature for a prolonged period of time, then its supply of heat production fails to match the heat loss. Approximately ninety percent of the body heat is lost via skin and 10 percent via lungs.
The longer the body is exposed to the cooler surrounding, the more the heat losses from its skin. When the core body temperature reduces to 35 °C (95 °F) and continues to plummet then hypothermia ensues.
If no measures are taken to prevent heat loss, hyperthermia progress from mild hypothermia with temperature range 32°C – 35° C or 90 – 95° F to moderate hypothermia with temperature range of 28-32° C or 82-90° F to severe hypothermia with temperature range of 20-28 °C or 68-82° F.
With continuous heat loss and scanty production of heart during prolonged exposure, human body is faced with difficult decision — whether to keep on supplying blood to toes and fingers and the peripheral organs or to save the meager supply of blood to keep the precious heat in the core to warm heart, lungs, kidney and other vital organs. With plummeting core temperature, body frantically chooses the latter and cuts off the blood supply to fingers and toes and the extremities to save heat to keep the heart and lungs warm.
The cells in the toes and fingers, not getting the blood supply are unable to warm them, begins to die through a process called necrosis whereby first ice crystals are formed in the space outside the cells, water is lost from the inside of the cells and causing the cells to dehydrate. The affected area becomes numb and insensitive and appears darker and black with the formation of what is known as gangrene. This is what the untreated form of frostbite is.
To prevent the further death of the extremities, the frostbitten extremities need to be amputated. The severe the hypothermia the extensive the frostbite is, sometimes up to ankle and palm. The nose ears and cheeks are vulnerable to frostbite too.
As the exposure to cold continues, the heart begins to slow down and supply less blood to the organs in order to keep the metabolism to the minimum so that the loss of heat is minimized.
This causes the brain cells to get less blood and thus less oxygen to its cells. The cause the person to be delirious and unconscious. Brain is the largest consumer of the blood and the oxygen. It may just have 5 percent of body weight but it consumes 20 percent of blood supply.
The kidney getting less blood produces less urine begins to fail leading to kidney failure. The entire human machinery slows down.
When the internal temperature falls sufficiently below, electrical conduction that maintains heart beat is severely disturbed. This causes heart’s ventricles to pump erratically and inefficiently. This leads to the dreadful ventricular fibrillation incapacitating the heart and failing it to pump.
As the heart fails to supply blood to the brain, the cells of the brainstem die stopping the respiration. Thus the person dies.
This way, a person exposed to cold environment for an extended period of time dies because his heart falters and fails to supply oxygen to the cells in the brain stem that regulates the respiration.
The death of the thousands of soldiers of the Napoleon army in 1812 and the Nazi in 1941 when each of them had advanced to Moscow to invade Russia has been widely attributed to the hypothermia and frostbite that their soldiers had to face due to harsh winter weather.
Elderly people are more susceptible to hypothermia because their ability to regulate temperature and to sense cold or heat decreases with age. They are often the first victims of severe cold weather condition during winter. Infant, toddler and young children too are susceptible to cold and hypothermia.