SCUBA DIVING EXPLAINED
Questions and Answers on
Lawrence Martin, M.D. Copyright 1997
Brief History of Diving
Stress, Hyperventilation, and Hypothermia
WHAT IS STRESS?
Stress is a term frequently used by divers to describe uncomfortable or dangerous experiences. The dictionary defines stress as "physical, mental or emotional strain or tension." The diver who says "I was stressed" usually means something like: "I found myself in a difficult situation and was uncomfortable, anxious, fearful." Or, "I was not in full control of the situation, my heart was pounding, and for a while I felt pretty tense." The sudden onset of stress is usually accompanied by specific physiologic changes such as sweating, headache, fast heart beat and over breathing (hyperventilation).
WHY IS AN UNDERSTANDING OF STRESS IMPORTANT FOR DIVERS?
Stress is such an important concept in diving - avoiding it when possible, confronting stress without panic when it does occur - that the subject is an integral part of "Stress and Rescue" courses offered by the scuba training agencies. Recognition and proper handling of stress are keys to safer, more enjoyable diving.
Stressful situations leading to panic probably account for many preventable fatal scuba accidents. In Stress and Rescue courses divers are taught that in any stressful situation you must STOP - BREATHE - THINK - ACT, in order to avoid a panic reaction.
|1. Someone who has symptoms from "hyperventilating" will always
have:(choose one answer only)
a. a fast breathing rate
b. deeper breathing then normal
c. numbness or tingling in the fingers
d. an arterial PCO2 lower than 36 mm Hg
e. a history of anxiety
|2. An open water scuba student goes to 30 fsw with his instructor. After about five
minutes the student finds it difficult to inhale through his regulator and starts to
breath fast. The student gives an out-of-air sign and the instructor signals him to
surface. On the surface the student appears anxious and is noted to be breathing fast. The
instructor helps him get back into the dive boat. The student complains of numbness and
tingling in his hands and around the mouth. What is the most likely cause of his problem?
|3. What is the principle difference between hyperventilating on land and while
TEST YOUR UNDERSTANDING Answers
WHAT IS HYPOTHERMIA?
Hypothermia is a lower than normal body temperature. Normal body temperature is about 37°C (98.6°F). Water temperature less than this will drain heat away from the body and, over time, cause hypothermia. The most susceptible areas for heat loss are the head, underarms and groin. This is why a hood is so important in cold water diving.
Water conducts heat about 25 times faster than air. Because of rapid heat conduction by water, and lack of much natural insulation, the human body cannot defend against low water temperatures as well as against low air temperatures. That is why 75°F in the air feels quite comfortable with light clothing, but the same water temperature requires a full wetsuit for comfort.
Normal body temperature is 37°C/98.6°F. For medical purposes, hypothermia is defined as a central body temperature equal to or less than35°C (95°F). Hypothermia can be divided into three stages based on the body temperature: mild, moderate and severe (Table 1).
|TABLE 1. CLASSIFICATION OF HYPOTHRMIA|
|Mild: 34 º - 36.5 ºC (93 º - 95 ºF)
Blood pressure usually normal but may be high or low; victim may have trouble speaking, walking, remembering; shivering often present when temperatures reaches 95 ºF.
|Moderate: 28 º - 33.5 ºC (82.4 º - 92 ºF)
Victim begins t lose consciousness; heart rate slowed; victim may have heart rhythm disturbance with low blood pressure .
|Severe: Below 28 ºC (82.4 ºF)
Victim in shock; no response to pain; very slow heart rate; victim at high risk for sudden death from heart rhythm disturbance
Up to a point we can maintain normal central body temperature when exposed to cooler temperatures, even though we may feel cold. Feeling cold or chilly is not the same thing as hypothermia, but may be a precursor to true hypothermia. True hypothermia is a medical emergency that, uncorrected, can be fatal. However, water temperature has a variable effect on a given individual; its physiologic effects depend not just on individual tolerance, which varies from person to person, but also on the length of the exposure and the type of protection worn.
For most divers, water temperatures above 90°F feel hot, and temperatures between 84°F and 89°F feel quite comfortable, at least initially. We often see divers enter water in the mid 80s without a wetsuit, or with only a non-insulating protective "skin" worn to avoid abrasions. Even so, heat loss is occurring at these "warm" temperatures, because they are still lower than normal body temperature. For each degree of water temperature lower than 84°F, an increasing percentage of people feel the need for thermal protection with a wet suit.
There are data regarding how long an unprotected person can stay immersed in water at various temperatures before hypothermia occurs; obviously the colder the water, the faster body temperature will fall and the more likely the victim will succumb. According to the National Oceanic and Atmospheric Association (NOAA), a body temperature of 91.4° F (33°C) is lethal for about 50 percent of all people who reach this level from water exposure.
Recreational divers in warm waters (>75°F) will likely not develop hypothermia during one dive. They may, however, feel chilled and uncomfortable, lose some body heat, and enter into a stressful situation. It is not a pleasant way to dive. The major warning sign of impending severe hypothermia is shivering, which usually occurs when body temperature reaches 95°F. The shivering diver should exit the water.
It is always better to have a little too much protection than too little. Protection for the diver means some type of worn garment covering most of the skin surface, either a wet or a dry suit. One can always open a wet suit zipper if the water feels too warm. Once chilled, however, there is little one can do except get out of the water.
A wet suit is a form-fitting suit, usually made of closed-cell neoprene, which means it contains air cells that are an inherent part of the fabric. The wet suit allows water to enter between the suit and the diver's skin. This layer of water is then warmed by the diver's skin and serves to retard heat loss during the dive. Wet suits, depending on their thickness and use of hood and gloves, can be protective down to the 50°F to 55°F range. Note that the closed air cells of neoprene are compressed with depth, so the wet suit loses much of its insulating ability the deeper one goes.
Below 50°F, a dry suit is usually necessary for proper thermal protection. (Some divers feel any water temperature less than 60°F mandates a dry suit.) No water can enter a dry suit, so the diver stays dry throughout the dive. A dry suit is typically composed of 1/4 inch closed-cell neoprene with nylon backing. Instead of water, a layer of air (delivered from the tank) is kept in place between the inside of the dry suit and the undergarments worn by the diver (thermal underwear is recommended). Boots are also an integral part of the dry suit. The amount of air inside a dry suit is controlled by the diver; since it can markedly affect buoyancy throughout the dive, special training is necessary for proper use.
The range of wet suit thickness' and temperature effectiveness are shown in the following box, compared with the dry suit. Note that the protection afforded by both types of suits will be enhanced if the diver also wears a hood and gloves. The neoprene wet suit sizes are based on the English system of measuring thickness. In most countries wet suits are marketed by metric thickness, e.g., 1, 3, 5 mm, so the corresponding thickness in inches will vary accordingly.
|TABLE 2. WET SUIT THICKNESS AND WATER TEMPERATURE|
|wet suit thickness:||water temperature|
|1/16||1.6||75-85 ºF / 24-30.5 ºC|
|1/8||3.2||70-85 ºF / 21-30.5 ºC|
|3/16||4.8||65-75 ºF / 18-24 ºC|
|1/4||6.4||50-65 ºF / 10-18 ºC|
|3/8||9.5||45-60 ºF / 7-15.5 ºC|
|Dry Suit||< 60 ºF / 15.5 ºC|
|* Tolerance to cold will vary according to the diver's body makeup, plus use of hood and gloves. There are no hard rules about what wet suit to wear at what water temperature ; It is largely a matter of preferences and diver tolerance. The temperatures shown are approximate ranges for comfort for the specified protective gear.|
WHAT IS THE TREATMENT OF HYPOTHERMIA?
You may be called on to assist or aid a hypothermic or chilled diver. There are formal hypothermia protocols and whenever possible victims should be handled by a knowledgeable professional. Issues such as CPR or hypoxia may also need management in any hypothermic diving injury.
Treatment of hypothermia can be divided into passive rewarming, active surface rewarming, and active core rewarming. In the field, away from a medical facility, you will probably only be able to accomplish the first two.
PASSIVE REWARMING - remove all wet clothing; use dry, unheated blankets, dry clothes, and a warm room environment.
ACTIVE SURFACE REWARMING - use heated blankets or hot water bottles applied to skin. If the victim is fully alert, give warm liquids; this will help correct any associated dehydration. Alcohol and caffeine beverages such as coffee and tea should be avoided. Immersion techniques, such as placing the victim in a tub of hot water, are not generally recommended.
ACTIVE CORE REWARMING (by medical personnel only) - instillation of warm fluids into the veins; placement of warm fluids through a tube into the victim's stomach; inhalation of warm respiratory gases; dialysis (removal of blood for warming outside body, then returning the blood to the victim).
|4. Listed below are four "mechanisms." Choose
the two mechanisms by which wet suits protect against hypothermia.
a. insulation (prevention of radiation heat loss)
b. thermal equilibrium between water under the wet suit and the diver's skin temperature
c. continuous circulation of water under the wetsuit and the diver's skin
d. compression of neoprene air cells with depth, which keeps heat from escaping
|5. What is the recommended procedure for a diver who feels chilled and
begins to shiver 10 minutes into a planned 40 minute/ 50fsw dive? The diver is wearing a
wet suit appropriate for the water temperature.
a. Stay as deep as possible to increase wet suit compression and thus thermal insulation.
b. Exercise by using arms in a swimming motion; plan for a somewhat shorter dive since this technique will increase air consumption
c. Tighten the BC to prevent flow of water between it an the wetsuit.
d. Ignore the sensation until your teeth chatter and you can no longer comfortably hold the regulator in your mouth.
e. Make a sign to your dive buddy that you are chilled and then exit the water. Expect your buddy to follow you up unless there is someone else he/she can buddy up with.
TEST YOUR UNDERSTANDING Answers
WHAT IS HYPERTHERMIA?
Hyperthermia, or over heating, is much less common than hypothermia. The main reason is that open water (oceans, lakes, rivers) is naturally cooler than body temperature. However, while wearing a thick wet suit on hot days, any diver can become overheated and develop true hyperthermia out of the water. The body temperature rises, which is the same as developing a fever. The threshold body temperature that puts the diver at risk is about 102.2°F (39°C). Signs of hyperthermia include rapid breathing, feeling warm or hot, mental confusion, fatigue, muscle cramps, nausea, and exhaustion.
The higher the temperature above 102°F the worse the problem. Hyperthermia is considered life threatening whenever body temperature reaches 105-106°F; such a fever places the diver at risk of cardiovascular collapse, shock and death. Treatment requires that any wet suit be removed as quickly as possible. If recently in the water the diver will be wet, but the skin will be warm and pulse rapid. (If hyperthermia occurs before entering the water the victim will appear hot and dry, with flushed skin and a rapid pulse.)
The major complications from hyperthermia are dehydration and shock. Emergency first aid requires cooling the body temperature by any means available: wrapping in a wet blanket, immersion in water, spraying with cool water. Generally the body temperature should not fall below 101°F, as too rapid cooling can precipitate hypothermia. Since a thermometer may not be available in the field, it is best to cool the person slowly rather than quickly.
Answers to TEST YOUR UNDERSTANDING
1. d. Of the answers provided, only a low PaCO2 is invariably present, since it is part of the definition of hyperventilation. All of the other symptoms are often found, but are not part of the definition (they could be due to other causes, including DCS.
2. Hyperventilation. Although hyperventilation and the bends may be difficult to distinguish after a dive, in this situation the shallow depth and short length of time virtually rule out the bends.
3. On land you cannot run out of air so hyperventilation, per se, is not life threatening. Under water a hyperventilating diver can run out of air, panic, or have some other catastrophe, and thereby risk drowning.
4. a. and b. Note that answer d, compression of neoprene air cells at depth, actually diminishes the wet suit's thermal protection.
5. e. Exit the water. Exercise is likely to worsen the hypothermia since it brings cold
blood from the extremities to the central part of the body.
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