Environmental Physiology: Cold

Homeotherms

Organisms, such as humans, that use behavioral and physiological mechanisms to regulate their core temperature.

Core Temperature

The temperature of the hypothalamus, is the site of temperature regulation in the body. The resting temp is 36.5-37.5. During exercise, Tc can rise about 40 degrees C and increases proportionally to exercise intensity

Ways to measure Core temp

Rectal and esophageal probes. Pills that are swallowed and send a temp signal from gastrointestinal system

Skin Temperature

The temperature of the skin, can be influenced by environmental factors, metabolic rate, clothing, and hydration state. Measured with dermal patches

Hypothermia

A condition where the core temperature is below 35 degrees Celsius. The body's core is the brain, heart, lungs, blood, liver, and kidneys. Critical areas for heat loss is , the head, neck, side of the chest and groin. Shivering will cease when the core temp is below 32-34 degrees and Death occurs when Tc drops to 24-28 degrees

Heat Exhaustion

A condition where the core temperature is between 38.5 and 40 degrees Celsius.

Heat Stroke

A condition where the core temperature is 40 degrees Celsius.

Mechanisms for Heat Gain

Basal metabolic rate, thermic effect of food, shivering, environment, radiation, conduction, and convection.

Mechanisms of Heat Loss

Radiation, conduction, convection, and evaporation.

Radiation

The exchange of electromagnetic energy waves emitted from one object and absorbed by another.

Conduction

The transfer of heat that occurs whenever two surfaces with differing temperatures are in direct contact.

Insulators

Materials that do not conduct heat readily, such as still air. The rate of conductive heat exchange is inversely related to the thickness of the insulating substance

Convection

The transfer of heat requires one of the media to be moving, as occurs with a fluid or gaseous medium. How heat transfers from skin to moving air or water. Temp gradient between skin and air/water velocity are important factors in determining convective heat loss. Convective heat/loss gained during swimming more than twice than still water

Evaporation

The transfer of heat from the body surface through the change of liquid water on the skin to gaseous water vapour in the environment.

Increase in Metabolic Rate

A physiological response to a cold environment that involves an increase in heat production through voluntary exercise (increases heat production 10-20 times the basal rate) or involuntary shivering (increase by 3-4 times the basal rate)

Increase Tissue Insulation

A physiological response to a cold environment involves vasoconstriction of peripheral blood vessels and shunting of blood flow into deeper vessels to retain heat. Blood flow stays deeper so retains heat and when its too hot blood reaches the skin to give off heat. Superficial Blood vessels in the head don’t contraction, so the head is the most important source of heat loss, accounts for 30-35% of total heat loss

Behavioural Responses to Cold

Actions taken by individuals to protect themselves from the cold, such as wearing clothing, seeking shelter, or starting a fire.

Factors Affecting Response to Cold

Skinfold thickness, gender, clothing, and wind penetration.

Cold Injuries

Hypothermia and frostbite, which can occur due to prolonged exposure to cold temperatures.

Effects of Cold on Performance

Decreased strength, power, flexibility, cardiovascular endurance, nerve conduction velocity, reaction time, and manual dexterity.

Primary physiological responses used by human to defend against a cold environment

Increase in metabolic rate and increased tissue insulation

Skinfold thickness

Thicker the fat layer, the greater the insulation

Gender

Women have more subcutaneous fat than men, therefore more insulation. But women and children have a larger surface area to mass ratio than men. women lose heat more rapidly than men in cold water

Clothing

Effective insulation given by clothing is a function of the air layer next to the skin, the thickness of the clothing and the air trapper between the layers of clothing. Insulation is reduced if it is wet. Outer layer should be water repellent and wind resistant, middle layers provide insulation and innermost layer provide insulation and wick moisture away from the skin

Factors associated with hypothermia

• Immersion in cold water or wet clothing

• Wind

• Physical exhaustion

• Inadequate clothing for conditions

• Lower percent body fat

• Hypoglycemia

• Alcohol consumption

  • Decreases in shivering, increase blood flow to skin and impairs judgement

Hypothermia causes the oxyhemoglobin dissociation curve to shift left

Increased hemoglobin affinity for O2 > less O2 is released to tissues > body tissue shift to anaerobic metabolism >hypoxia of heat and brain plus metabolic acidosis > depressed brain function and cardiac output > ventricular fibrillation and death

Frost bite

Freezing of superficial tissues that occurs when skin temp reaches -2 to -6 degrees C and Many are unaware of frostbite because the sensory nerves are blocked and skin is numb

Cold Exposure and Expiratory tract

Inhaled air is conditioned as it enters the upper respiratory passageways, warmed to 37 degrees C. Can't freeze your lungs when exercising in very cold weather and is very dry possible causing throat irritation

Cardiovascular Endurance In the cold

Optimal temp is 14 degree for best performance, More circulation is directed to working muscles and less is required for heat dissipation. Due to increase metabolism and heat production with this exercise but A drop can occur with very low intensity duration walking or trekking. If TC does drop, there is less reduction in aerobic performance

Cold Exposure

Cold-water immersion can result in a more dramatic and rapid heat loss. Water is 25* more conductive than air. Survival for more than a few hours in unlikely even in water that is 10 degrees C