When Janis Joplin wasn’t screaming into the mike, her voice was more than just a captivating sound, it was a mysterious and passionate mezzo-soprano vocal that resonated with all the influences of her troubled life. Her songs carried a raw emotional quality that was a powerful mix of blues, rock, and soul. Janis’s life was way too short for her talent; she tragically died of a heroin overdose on October 4, 1970, she was just 27 years old (coincidentally the same age as both Jimi Hendrix and Alan Wilson, who also died of drug-related deaths within a few weeks). Of all Janis’ music, one tune always sticks out in my mind: her cover of “Summertime“ from the timeless 1930s folk opera Porgy and Bess, written by George and Ira Gershwin. Her throaty rendition is hauntingly ethereal and can make your skin crawl from its raw emotion. The song starts off, “It’s summertime and the livin’ is easy, fish are jumping and the cotton is high.” But the kind of summer we’re having here in South Florida—and in most of the country too—isn’t so easy, especially the impact it can have on us pilots due to high heat and humidity and all the negative impacts to our overall health and cockpit performance. There are really important things you have to do to avoid heat-related problems in your everyday activities and especially when getting into your airplane.
The human body can properly function only within a very narrow temperature range, about 4oC. When core body temperature is below about 35oC or above about 39oC, the biochemistry and physiology of our cells and organ systems start to fall apart. Children are a little different and can tolerate higher fevers, but those levels would cripple adults. The body stays within that narrow temperature range with a biological “thermostat” called the “hypothalamus,” a small structure buried deep in the center of the brain. It functions with incredible precision, detecting body temperature changes as little as 0.01oC and triggering a cascade of physiological responses before you even realize you’re warming up or getting too cold.
There are three mechanisms that the hypothalamus gland uses to cool you off when it detects a rising core temperature. The first one we’re all familiar with, is sweating; the second is more subtle and involves vasodilation of the small arteries and veins in the skin. The body has sweat glands in the skin that receive signals from the brain that stimulate the release of water and electrolytes onto the skin surface. As sweat evaporates in the breeze, it carries away body heat with it and lowers our core temperature. The second thing our bodies do to cool off is something called “cutaneous vasodilation.” Blood vessels near the skin surface widen (dilate), routing warm blood close to the surface where it can radiate off heat. Also, with evaporation of sweat that has cooled the skin, the shunted blood runs through a cooler area and is carried back to the rest of the body, further helping in cooling. That “flushed” appearance of someone who’s been running hard is the surface look of vasodilation as the skin acts as a radiator, the same look you get on any hot day out in the sun.
This explains why the combination of heat and humidity is so dangerous to this intrinsic cooling system. We all studied aviation weather in our training and remember the basics of temperature and dew point—the warmer the air, the more water vapor it holds. But when the air is saturated with water it’s not possible to add more water vapor to the atmosphere. That means that sweat doesn’t evaporate and carry away with it rising body temperature. It’s also why we feel so much more uncomfortable in high humidity and TV “meteorologists” tell us that it’s 85o out but it “feels” like it’s 95o. Muscle activity generates heat—that’s why we shiver when it’s cold out. It’s also the basis of the third mechanism the hypothalamus uses to cool us off. The brain sends “slow-down signals” to our body that influence behavior, essentially making us feel bad so we ease up on activities and decrease muscle activity.
A much more serious aspect of raising body temperature is brain overheating. It’s more subtle and more dangerous since it impairs cognitive function, and that can start well before the body reaches dangerous core temperatures. When the brain overheats, “brain fog,” that we’ve talked about before, sets in, negatively impacting thinking and problem solving, data processing, and memory. None of that is good in the cockpit and can be a potential source of fatal mistakes. If you’re lucky enough to have an air-conditioned airplane you can at least cool off when you fire up the engine, but if you don’t have that luxury, you run the risk of raising your body temperature pretty quickly, long before you get off the ground, and can start off your flight not thinking clearly. When this cooling system breaks down, the consequences range from uncomfortable to life-threatening, something known in the popular vocabulary as “overheating.” The technical name for this is “hyperthermia,” that can progress from confusion and dizziness to seizures and organ failure within hours. For all the reasons above, this carries huge risks for safety in the air.
This leads us into the topic of things we can do to avoid overheating in the first place and help cool off when outside in the heat. The most obvious thing is to limit time in the sun and heat and cover up, as there’s a lot of heat absorption with the sun beating down on your head. Wear a hat on the ramp for your pre-flight inspection or keep your plane in the hangar or the shade till you’re ready to go. During exertion in hot conditions the human body will produce up to two liters of sweat per hour. That’s a combination of water and electrolytes that need to be replaced. The kidneys are responsible for body fluid balance; when you get dehydrated the kidneys stop excreting fluid—urine—so an important metric of normal hydration is urine output. Your brain will remind you that you’re getting dehydrated by making you feel thirsty, but also keep track of trips to the bathroom. If you’re not going to the bathroom much, or your urine is very dark and concentrated, you’re underhydrated. So, when you’re out in the heat—drink plenty of fluids until you have to pee a lot—it’s that simple. You have to replace those two liters of sweat by drinking water or a balanced electrolyte solution, the colder the fluid and more ice in the glass the better.
The main electrolytes you lose in sweat are sodium, chloride, and potassium, and if it’s really hot out you can deplete levels of magnesium and calcium. The main ingredients of most balanced electrolyte drinks are water, sodium, potassium, and glucose. The electrolytes not only replenish what you lost but they help your stomach and intestines pull water into the bloodstream faster than plain water. Most adults should be aiming for around 2-2.5 liters of fluid on a hot day, but you might need more. There are lots of fruits and vegetables that contain a good balance of the electrolytes that we lose in sweat and are something to add to your diet. Bananas, potatoes, and broccoli are rich in potassium, and fruits like watermelon are easy to carry in the cockpit and pleasant ways to add fluids. Another really important thing is to limit alcohol intake and caffeine drinks, since both are diuretics that will cause further dehydration. Keep track of your prescription meds too. Obviously, diuretics and other blood pressure meds can worsen dehydration, as can a whole list of meds for other conditions. Check with your doc and the labels on your prescriptions to be sure. Special care needs to be used if any of your meds are administered by transdermal skin patch, since absorption of the medication will be altered by sweating and dilation of blood vessels in the skin, that can lead to overdosing or underdosing of those time-release formulations. Since almost all medications are ultimately excreted by the kidneys, if you get dehydrated and are not making much urine, blood levels of drug metabolites can rise, also affecting the concentration and dose of those meds in your body.
Make summertime livin’ easy again with some simple, common-sense things to protect yourself in the heat. Limit exposure and exertion, cover up, “pre-hydrate” in advance of any exertion on hot days and drink lots of balanced electrolyte fluids, avoid alcohol and caffeine, check your prescriptions, make sure you’re making lots of trips to the bathroom, and cool your brain down before you take off so you can think clearly. And as always, FLY SAFE.
