When the body is exposed to intense heat, the consequences are severe and… — Page 134, Lesson 209

I want to walk you through the physiological side of stress, specifically how temperature extremes and internal body states affect the human body in aviation. We've already covered the general concept of stress; now we're drilling into the physical mechanisms that can degrade a pilot's performance. Let's start with extreme heat stress. When the body is exposed to intense heat, the consequences are severe and progressive. The first major effect is cell damage, especially within the brain. That's critical for a pilot because cognitive function is everything on the flight deck. Next, you can develop heat stroke, which is a life-threatening condition where the body's temperature regulation fails. If it continues unchecked, it leads to coma, and ultimately, if the blood temperature rises to approximately 43°C (110°F), death will result. That's a hard physiological limit. There's an important note here: generally speaking, the mind and body need an average of 2 weeks to acclimatise to a hot and humid environment. So if you're a crew member who's just arrived in a tropical climate, you are not fully adapted for about two weeks. During that period, your tolerance to heat stress is lower. Now, let's flip to the opposite end: extreme cold stress. The key metric here is core temperature. If the core temperature drops to approximately 35°C, shivering declines and eventually ceases. That's a dangerous sign because shivering is the body's last-ditch effort to generate heat through muscle activity. The effects of extreme cold are listed in a specific sequence. First, you get uncontrollable shivering and an associated need for more oxygen. Around 34.5°C, that shivering, which will have started earlier, tends to cease. That's the point where the body is giving up on generating heat. Then you see cell damage, especially of the brain, just like with heat. Next comes sleepiness associated with a feeling of contentment or apathy — this is extremely dangerous for a pilot because you lose the urge to fight the condition. You also get circulatory impairment and degradation of the sensory nerves, meaning your hands and feet lose dexterity and feeling. Then severe damage to the skin and tissues, which is frostbite. Finally, coma and death. I want to stress something important here: the effects of exposure to extreme temperatures are not restricted to those dramatic conditions I just described. Smaller temperature variations within these limits can have a detrimental effect on a person's ability to perform a task. So even a mild cabin temperature that's a few degrees off can degrade your performance, even if you're not in danger of heat stroke or frostbite. Now, moving to internal physiological factors. These are stressors that originate inside the body. The most important ones are: hunger, thirst, fatigue, lack of sleep, and pain. With the exception of pain, these factors are normally within the control of aircrew. You can choose to eat, drink, rest, and sleep before duty. It is of fundamental importance that crews ensure they never start a period of duty with any of these internal physiological stressors. That means pre-flight preparation isn't just about the aircraft — it's about your own body state. If you're hungry, thirsty, tired, or sleep-deprived, you are already degraded before you even strap in.