It used to be that only mad dogs and Englishmen went out in the noonday sun. These days you might see anybody who owns a pair of Reeboks pounding around the track, down the street or through the park, working hard to live forever, paying no mind to the current heat wave.
So he looks a little pink, like a lover engulfed by a blush. It probably won't kill him -- not if he's in shape, accustomed to the climate and has been pumping fluids into that most efficient and adaptable of machines we call the human body.
If he's not in shape, has recently lived in Alaska or has refrained from water and such, he could be in trouble.
What precisely is happening to our determined jogger, this macho jock undeterred by Fahrenheit levels approaching 100?
This kind of heat has already killed well over 100 people in the Deep South and Western states, and it has finally found its way here. Yesterday it reached 98 degrees by 4 p.m., with a heat index of 102.
The jogger's blood is doing its best to rescue him from his brain's recklessness, in deciding he should exercise in weather like this. Blood is flowing out from the core of his body to the surface of his skin so the heat being generated within his body by his exertion can be dissipated into the air.
Body's response
The red color -- the blush -- is evidence of the dilation of the capillaries on his skin; they are filling up with this large volume of blood.
Now, according to physicians and physiologists this is good. It is the body defending itself. And the body has an array of specific physiological defenses against heat besides this, things like heat-shock proteins which are being produced in the cells to protect them from heat stress.
As with all defenses, this one, the migration of the blood, has its limitations. In this case, the limitation relates to the supply. The blood engaged in getting rid of the heat at the surface of the body has to come from somewhere, right?
So where does it come from?
From vital organs like the kidneys, the brain, the heart. These need fresh blood, too, and don't like being deprived. Take the heart, for instance. With so much blood out on the periphery of the body, it has less to pump. So what happens?
Artin Shoukas, a physiologist and biomedical engineer at Johns Hopkins Medical School, explains the sequence: "Your blood pressure decreases. You start to feel faint. And, usually because you are standing, you don't have enough blood going to the brain. So you faint."
