Chapter 4- Diving Physiology Diving Physiology 129 C F Diver will Overheat Resting Diver will Overheat Working features including your size and amount of body fat. Exercise and shivering increase your heat production. Agitation of cold water by your activity increases your heat loss. It is not always the case that exercise in cold water makes you colder, however. While exercise in the water causes heat loss to the water, you are still producing heat. It depends which prevails. An easy, though oversimplified scheme is to consider your body a central core of your brain, spinal cord, and organs of your chest, abdomen, and pelvis, surrounded by a peripheral shell of your limbs and skin. Your body controls your core temperature within narrow limits and changes your peripheral shell temperature greatly in response to environmental temperature. Normally, your core is far warmer than the skin of your shell. The familiar 37°C/98.6°F number is the temperature of your core, not your skin. Your skin is far cooler and will change with surrounding temperature. That is one of the ways you conserve your core temperature. Your skin cools to close to ambient temperature to reduce the difference between your shell and the environment. That keeps your heat loss gradient small and reduces your heat loss. People with high skin temperatures are losing a lot of heat to the environment. It is not necessarily true that cold hands means poor circulation. Cool skin temperature, within limits, is a crucial heat-conserving mechanism. The fact that your skin temperature is cooler than your core also means that it is not true that any water cooler than 37°C/98.6°F would chill you. You can overheat in water warmer than your skin temperature. Head heat loss is not the majority of heat lost, as popularly thought. Head heat loss is less than one-third to one-fifth of your total body heat loss. It also is different in different temperatures, and with different amounts of exercise. Still, head heat loss is a good amount considering that your head is only about 7-9% of your body total surface area, but some people have bigger heads than others, and balding increases head heat loss. Your susceptibility to chilling increases, obviously, the longer you stay in cold water and the colder the water. Susceptibility also increases if you are dehydrated, tired, hungry, sick, out of shape, very thin, have been smoking, or are using drugs or alcohol. Effects: Effects of chilling vary with people and conditions, and can range from mild, to severe, to fatal. Very mild chilling can occur in relatively warm, even tropical waters, over repeated dives with no thermal protection. Shivering or overt signals of cold may not occur and you may not recognize the problem, but the subtle heat drain from your body continues. You may become tired with no desire to continue your diving or anything else. In colder water, your hands can become useless if not protected. You may not be able to signal for help or rescue yourself or others, even if your core temperature is unaffected. Core chilling is often categorized for convenience as follows: 1. Mild Chilling. Core temperature 36.1°C/97°F to 37°C/98.6°F. Feeling cold, shivering, clumsy hand movements, and able to talk. 35 90 Unprotected Diver Comfortable During Moderate Work Full Wet Suit or Dry Suit Required 80 70 60 50 40 30 30 25 20 15 10 5 0 -5 FIGURE 4-18. TEMPERATURE PROTECTION CHART IN DEGREES CELSIUS AND FAHRENHEIT.
20047TC
To see the actual publication please follow the link above