A HEATED CONVERSATION AWAITS
In two previous posts we have learned about hostile environments in general, and dived deep into hot hostile environments and how they put the body at risk of death. This post will focus on the mechanisms that the human body uses in order to lower its core body temperature, and dispose of internal heat.
A hot environment could be defined as one in which the environment’s temperature is
greater than that of the body, while a hostile and hot environment could be defined as one in which the environment’s temperature is significantly greater than that of the body, which could put one’s health/life in danger. in addition, hostile environments tend to be challenging as it pertains to water and food resources.
The basic principle behind the idea of existence and/or exercise in a hot environment is one of a simple temperature gradient with three optional outcomes: 1) The environment is hotter than the body - the body takes in heat; 2) The body is hotter than the environment - the body loses heat; 3) The body is equal in temperature to that of the environment - heat does not change its location.
Advertisement
In order for heat to be disposed of, it must make its way to the environment. As long as the heat is inside the body or on it, we cannot consider ourselves rid of it. Thus, the body's mechanisms of heat disposal are directed at translocating heat from internal organs to the skin. The next goal is to have the environment absorb the heat into it.
A core body temperature greater than 40ºC/104ºF is dangerous, while a core body temperature of 42ºC/ 107.6ºF or greater can be deadly. Body core temperature is supervised and regulated by the Hypothalamus gland, since heat production in our body is mostly achieved via deep internal organ activity (brain, liver, heart) and skeletal muscle contraction. Physiological heat production is mainly governed via hormonal means in the form of inefficient heat production.
Heat loss is governed via five processes: 1) Thermal Conduction; 2) Thermal Radiation; 3) Thermal Convection; 4) Thermal Evaporation; and 5) Respiration. While all five as used to dispose of heat, one of the processes tends to be more dominant as a response to the circumstances. As circumstances change, so does the dominant heat disposal mechanism.
Next, let's define and explain each one of the five heat disposal mechanisms: 1) Thermal Conduction – the transfer of heat energy arising from temperature differences between adjacent parts of a body; 2) Thermal Radiation – radiation emitted by a heated surface in all directions and travels directly to its point of absorption. Thermal radiation does not require an intervening medium to carry it; 3) Thermal Convection – heat is transferred
by movement of a heated medium such as air or water; 4) Thermal Evaporation – a phase change whereas heat leaves the liquid it was in, to be absorbed by the environment; 5) respiration - heat is lost to the environment by breathing hot air out from our mouth or nose.
The hotter it gets, the more we relay on sweating to lose heat to the environment and “cool down” via evaporation, while the need to sweat so evaporation can take place, is regulated according to core(internal) body temperature (not the temperature of skin). Conduction and respiration (breathing) stay the same with very slight changes, while radiation begins as the dominant mechanism to lose heat and decreases to almost nothing as it get hotter outside.
Convection decreases slowly from being the 2nd dominant mechanism of losing heat. Greater humidity reduces the lose of heat via sweating, since the environment is highly
saturated with water vapor and cannot absorb more water (sweat is mostly water + NaCl).
Thus, in humid environments, our core temperature increases faster. For example, getting your cloths wet does not help, since the water does not evaporate, leaving the heat on our body. The best environment, that promotes heat loss, is either an environment colder than the body's core temperature, or an environment with plenty of wind and dry air (the least saturated with water vapor).
For populations that are most likely to have functional problems existing and/or exercising in a hot environment, evermore so in a hot and hostile environment are 1) Children; the younger the worse off they are; 2) The elderly; the older the worse off they are; 3) People with obesity, since fat is an insulator tissue; 4) People with health problems, especially cardiac and kidney diseases.
Graph: changes in the dominancy of body heat disposal mechanism (Watts) according to the temperature of the environment (degrees Fahrenheit).
Hyperthermia is a term that represents a higher than normal body core temperature; It can be a normal response to exercising or a clinical sign (fever, heat illness, other). If unregulated and uncontrolled, it can be deadly. Even when it is in light of a clinical reason, hyperthermia, still might be a reaction that helps the body. For example: immune induced hyperthermia in response to a fever to help fight an illness. There is a difference between “low-grade fever” and “high-grade fever” in their clinical implications.
It is suggested to distinct between two different scenarios of exercising in a hot environment, by dividing them into two major dynamics: 1) With external means (water, nutrition, temperature regulation means and clothing); 2) Without external means. External means allow you, if planned smartly, to intervene and make up for the lack of natural physiological abilities, as the body is tested under extreme conditions.
Advertisement
Adaptation to heat, as is the case with all adaptations, must include multiple exposures to the conditions you wish to adapt to. Proper adaptation requires at least 14 days of constant exposure to the actual environment and conditions one wants to be acclimated to. Function at all levels is most-likely less then it would be in a non-hostile environment. Some people experience “pseudo-chills” due to the over-heating of the nervous system, which while dysfunctional, acts as if the body is experiencing hypothermia (abnormal low body temperature; the opposite of what is actually occurring)…
The following schematic shows how hostile hot environments create a death-loop or death trap, without external means as described above (also see a previous post explaining in detail how this happens):
Comments