interpreted by viewers to have different meanings.
Same lines, different perceptions. Many can learn
to see the opposite interpretation of the pictures.
Some can flip the interpretations back and forth,
seeing one and then seeing the other. A few are
unable to see anything but their first interpretation.
There is no dishonor or disloyalty or lack of
intelligence in the viewer who sees one picture
but does not see the other view.
The question to ask is not, "Is this view right and
the other wrong?" But rather, "Is this other view a
useful interpretation that enables greater capacity
for discover, analysis, prediction or control?"
Perspectives on Diving Physiology and Pathologies
Traditionally, we have viewed the problems of diving and diving medicine as related to the
behavior of gases under various pressure conditions, hypothermia caused by heat loss to the
aquatic environment, and narcosis caused ostensibly by saturation of tissues with inert gases such as nitrogen.
What is submitted here is the consideration of an hypothesis that all of the above phenomena
are related to a special case of hyperthermia. That is, that in diving we have a special case of extreme thermogenesis, or fever, and that the symptoms of narcosis, the bends, and the deliriums of the deep are intrinsically related to an elevated biological thermodynamic state.
Let us begin with information familiar to all divers and physicians treating diving and diving illness:
1. Water has approximately 25 times the thermal conductivity and 1000 times the specific
heat of air.
2. Both reports by divers and direct measurement show an apparent hypothermia--as evidenced
by reduced body temperature-- in response to exposure in cold water.
3. The deeper the dive, the colder the water encountered.
4. Heat loss is so great, that at 60 foot depths in cold water, a diver without exertion
will burn 3,000-4,000 calories within 20 minutes.
5. With repeated dives, a longer decompression time is called for.
6. Diving in warm waters skew the accuracy of the standard diving tables, i.e. warm
surface waters increase operating "depth" by 10 feet or more in reading the tables.
7. There is often a delayed response in presentation of symptoms of diving sickness.
8. Simple recompression is often insufficient to normalize physical functioning.
We can all agree that the above has been the historic experience of researchers and divers.
What has not been considered previously are the physiological mechanisms of thermogenesis
and how they would come into play in a diving situation.
Specifically, we must consider the following well documented and accepted perspectives on
the mechanisms of thermogenesis:
1. Under pressure, biological heat production increase to the extreme limits of biological
tolerance.
2. Symptoms of heat prostration in response to increased pressure include anemia, chills,
fever, delirium, failure of sweat mechanisms, an increased reliance on respiration
for heat loss to the environment, neurological and metabolic disturbance, change in
blood fluid distribution, chemistry and viscosity.
3. Sudden and rapid heat loss triggers increased heat production--thermogenesis--to
maintain the hypothalamic temperature "set points" of body temperature.
4. Individuals acclimated to high altitudes (low pressure) develop fevers when going to
lower altitudes (higher pressure) due to the greater saturation of blood with O2
and due to the increase in pressure.
5. Individuals with extreme fevers report sensations of extreme cold and chilling due to
the rapid rate of heat loss to the environment. Delirium during fever is not uncommon.
6. Individuals who have been subjected to extreme heat or high fevers develop anaphalaxic
stress in repeated, and often, in single exposures. That is, the physiological
response to new heat stress becomes more acute with less stress and requires greater
efforts to self correct even after a single episode of high heat stress.
7. With extreme or repeated heat stress, hypothalamic set points for temperature,
fluid distribution, electrolyte balance, respiration and heart beat are altered.
New set points are defended by the body or resist resetting in much the same way
that original set points are maintained.
8. During heat stress, the lungs become a major heat exchange site. Rate of exchange
across the lungs is determined by the rate and degree of thermogenesis and the
heat exchange capacity of the inhaled gas (air or other).
9. Body fat acts as insulation. Individuals with low fat content will lose heat to the
environment more rapidly and require a significantly greater rate of thermogenesis
to maintain body temperature.
10. While exercise increases heat production, it can also increase the rate of heat loss
to the environment. In some circumstances, exercise may become a counter-productive means of heat generation.
11. Temperature is not a measurement of heat or the rates of thermogenesis and loss.
What temperature measures is a site and time specific conductive energy.
Heat is a measure of energy and its movement. Think of a thermostat controlling a furnace.
If the thermostat is set to 70 degrees Fahrenheit, the thermostat will turn the furnace on
and off as the environmental temperature exceeds or is below the "set point". If, however,
the windows and doors are open and a blizzard is blowing through, the temperature in the
room may drop far below the set point even when the rate of heat production is at its maximum limits.
If we consider the heat production factors effecting divers, we already know that the net heat production in cold water at 60 feet depth without currents or exertion utilizes 3,000-4000 calories in 20 minutes. In one hour this would be 9,000 to 16,000 calories or sufficient energy in air for five to eight days of normal activities.
Physiologically, this intense heat production is an unusual and extreme fever. It is the
rapid and efficient heat transfer to the aqueous environment that enables divers to
function during such extreme thermogenesis.
Endurance of the extreme thermogenesis and extreme heat loss in water varies with the
physiology and conditioning of the diver. Compression combines with the thermogenesis
to further increase thermodynamic activity. Exertion and the chill factor of water
currents act to further increase the rate of heat loss and demand for greater thermogenesis.
So great may be the heat generation that gases cannot be exchanged across the lungs and
toxicity if not asphyxia results.
Examining the decompression tables, it is clear that the rate and pattern of decompression
is more accurately an approximation of the time required to allow re-balancing of theoretic
heat production and heat loss factors in a theoretically uniform aqueous environment.
These theoretical models, however, are not a complete inventory of the factors which
determine the degree of solubility of gases in a liquid (Boyle's Law), nor the physiology
of the diver, his activities and energy state before and in the dive, or his
preconditioning to thermodynamic stress.
In the proposed model of diving as a hyperthermic phenomena, warm water dives must
logically have a different heat exchange rate than dives in cold waters. In warm water,
the rate of heat loss is reduced, therefore requiring more time to equilibrate with
biological heat production. The reduced rate of heat loss in warm waters presents
the physiological equivalent of a deeper, higher pressure dive. That is, more
physiological heat is present when either the rate of heat loss is diminished
(warm waters conduct heat slower and less efficiently) or the heat production
factors are increased (greater pressure at a deeper level).
If a system is beyond normal limits of heat production and tolerance, a reduced rate of heat
loss does not immediately reduce the rate of heat production. We acclimate to the heat
loss and thermogenesis occurring at particular ambient temperatures as well as different
pressures. Re-adjustment to both requires time and may be more complex than we have imagined.
Air travel shortly after dives has been known to trigger decompression sickness, and
recommendations are now made to avoid air travel for twenty four hours or more after diving.
Physiological adaption to reduced pressure are more than the effects of reduced pressure
triggering loss of gases or formation of embolisms: lower pressure causes increase in
production of blood --a condition requiring increased biological heat, greater liver
and bone marrow activity and altered respiration. Even pressurized commercial planes
are often flown with cabin pressure at 6,000 to 8,000 ft. altitude. Extensive testing
has identified that British, Swiss and Saudi airlines are the only commercial airlines
that keep in flight pressure at one atmosphere or standard sea level.
Anaphalaxic stress and loss of tolerance for heat can take many forms. A diver may complete
a dive successfully with no indication of stress, but hours later, after a high protein meal, the increase in basal metabolic activity may trigger symptoms of diving sickness.
The "specific action of protein" can raise basal metabolic rates some 30% within an hour
and maintain the elevation for 3 to 12 hours depending on the amount and type of protein
ingested. A hot tub or sauna, or other artificial heating of the body has a similar effect.
The effect is as if another dive is in progress, only the pressure keeping gases in solution and the heat loss of the aquatic environment is not present. The recent dive "conditions" the systemic response much the way exercise "conditions" the body for future stresses.
While we recognize the impact of previous dives on the systemic response to a new dive,
the interactive effects of other forms of thermogenesis on divers have not been explored.
In fact, the tremendous energy output of diving leads to encouragement to have large and high calorie meals, to warm up and relax using saunas and hot tubs, to press for greater physical strength and conditioning by aerobic exercising.
To Insulate or Not to Insulate
Wet Suits
In the model of diving as a hypothermic phenomena, the "problem" of longer dives has been
addressed as a need to insulate the diver from the heat loss to the environment. This has
resulted in new types of wet suits with greater insulation capacity. Unfortunately, divers
using these new wet suits have experienced more diving illness than the old suits.
In the new model of diving as a hyperthermia phenomena, the issues for divers shift.
On entering the water and reaching depth, greater insulation of a wet suit would decrease
the heat loss to the environment and the diver would experience greater comfort. On decompression, however, the rate of equilibration between thermogenesis and heat loss would be slowed by the insulation of the suit. This would make the diving tables more unreliable since readaption at various depths would vary based on the new pattern of thermogenesis and heat exchange. Decompression would be more often inadequate or incomplete.
Suits could be designed to increase the rate of heat loss on ascent from the dive or personal "monitors" designed to allow individualized patterns of thermal adaption to decompression to guide the diver.
Dry Suits
In the hypothermic model, the dry suit provides insulation from heat loss, but the divers
experience the thermogenesis of pressure. This leads to extreme heat production such as is
experienced in submarines, deep mines and other underground environments: Profound sweating,
difficulty breathing, need for cooling, changes in fluid balance, changes in metabolism,
during and after the dive and extreme fatigue on the order of heat stroke.
In the dry suit, respiration of compressed air becomes a major source of heat exchange.
The lungs become the coolest site, and the heat of the body moves mechanically to exchange
at the coolest sites. This causes changes in lung tissue, condensation in the lungs, and
may permanently effect the pulmonary capacity of the diver on land.
Redesigned suits that would monitor the heat generation and heat loss of the diver would
moderate the effects of the extreme thermogenesis of diving and its long term consequences.
With repeated dives, in either a wet suit or a dry suit, conditioning takes place that
results in heat sensitivity, more rapid aging, changes in cell structures and functioning
including changes in lung and nerve tissue, chronic dehydration, increased susceptibility
to infections, hypothalamic changes including altered set points for weight, respiration,
appetite, and libido. The extreme thermodynamic stress to the system may result in adrenal
exhaustion, kidney failure, heart and arterial disease, edema, and pulmonary disfunctions.
Personality changes accompanying these physiological alterations are not uncommon and may
be severe.
Professional divers who are diving in deep, cold water often many times in a day in dives
of an hour or more face the problem of becoming more adapted to living at depth than at the
surface. Indications of this would be phenomena such as sickling of red blood cells on
decompression or during mild fevers. Liver, spleen and circulatory problems and extreme
distress when at a higher altitude or low pressure environment--such as in an airplane--
are indication of profound alteration in the physiological mechanisms and even the
molecular structure of cells and tissues.
By understanding the true nature of the physiological interaction of a biological system
and the aqueous environments, a condition of hyperthermia or extreme fever-- we can develop
better means to secure the safety and health of divers.
Decompression and Thermodynamic Resetting
In febrile illness, the individual experiences an excess of heat production and heat loss.
He feels cold even when tremendous heat is moving through his system. The heat causes
low partial pressure of oxygen which in turn causes changes in circulation and respiration.
Heat increases the rate of nerve conductivity and can induce tremors or if persisted in,
paralysis and prostration. Extreme weakness, lethargy, dehydration and diminished respiration accompany the fevers. Following the abatement of the fevers, the individual may experience fatigue, emotional sensitivity, sleepiness and disinterest in surroundings and be specially sensitive to light and sound in the environment.
Medical treatment of fevers involve cooling the individual with tepid baths, administering of aspirin and other antipyretic drugs, rehydration, rest and protection from light and heat. In extreme cases, intravenous saline or Krebs solutions may be administered, salt replacement may be recommended, diets high in electrolytes and weak acids, and extended periods of rest with little or no exertion for weeks or even months may be recommended.
In diving, we may not have the time available to engage all of these gentle and relatively passive means of reducing heat in a non-aqueous environment. The life of the diver may depend on a definitive and orderly rapid reduction of heat. Several possibilities seem self-evident:
In water cooling: If a tub or tank can be filled with water and the diver placed in the tank, it will be found that the water warms very rapidly. The wet suit should be opened and gently
removed so that the optimum skin surface is exposed to the water. By adding cooler water to the tank and keeping the diver relatively calm and still, the higher thermal exchange with the water will cool the diver down.
The head is a major heat exchange site (about 30% of heat exchange is off of the head). The head should be kept wet, and an ice pack applied to the neck and lower portion
of the head. This will help protect the brain and central nervous system from the effects of extreme heat exposure.
It will be noted that a tremendous volume of heat will be radiated by the diver. Keep cooling until the diver feels peaceful and comfortable in the cold water and is breathing deeply and easily. sighing deeply, and generally emphasizing the expulsion of air rather than struggling to get air in or
holding the breath.
Ice Packs: As indicated above, the head is a major source of heat loss
to the body. To slow that heat loss, one may be tempted
to apply ice directly to the head. This is NOT recommended.
This would, in fact increase thermogenesis because, again,
the body registers the RATE of heat loss as an indicator
and prompter of thermogenesis.
Instead, one can apply cloth covered cold packs to the neurological lines approximately one inch to the right and left of the spine on the neck between the base of the skull
and the top of the shoulders. The skull itself should not
be cooled with the ice pack nor should the spine. There are deep thermal sensors in the spine that if activated trigger
rapid and profound thermogenesis.
Returning to land, the patient should rehydrate with pure water intake of at least one ounce of water per pound of body weight per day, avoiding alcohol, coffee and black teas, sugars and citrus fruit and juices (too many strong acids which heat the system by increasing free radicals) but taking freely of other liquids and eat small meals with low to moderate amounts of protein and carbohydrates for at least a day. As with febrile illness, avoid exertion, flying, trips to higher altitudes, hot tubs, saunas, electric blankets, sun bathing, tanning or other forms of manmade or natural heat and radiation.
Air conditioning presents a problem. While some moderation of air temperature to a temperate range can enable people to work and function more comfortably, the methods of air conditioning may cause greater thermogenesis to take place. Avoid blowers and fans that push air fast across the body. Air conditioning systems that pull air out of a room (as in turning the fan to face out the window) gives a more uniform shift and less of a "draft" upon the body. Thermostats should be set for no more than 7 to 10 degrees Fahrenheit below the air temperature. Greater cooling results in thermogenesis in most individuals.
Baths and showers should continue to be tepid to cool for a week or more.
As with any extreme of fever, the patient will not find this a comfortable regime at first. Our culture encourages people to stay warm even when the source of disorder or disease may be an excess of heat in the system.
Over several days, however, the individual will acclimate to the cooler regime and become aware of when they feel too warm and need to cool down. Eventually, the individual will enjoy the cooler bathing and living environment and find that they can self regulate more easily and recover more readily when presented with the stress of thermogenesis.
Divers can also begin to condition themselves prior to dives by cooling down in advance. That is, they can start to "flex" their ability to heat and cool by increasing their exposure to cold water as in swimming in cold water without wet suits; taking cool to cold showers and baths; taking air baths where they exercise in the nude; cooling the head and neck after high stress, exercising or high emotional stress. Keeping a rehydration schedule as a normal water intake using deionized or purified water to minimize stress to the kidneys. All of these actively condition the body to "reset" after a thermal stress.
Use of aspirin and other antipyretics should be investigated. The particular challenges of
individuals with medical conditions requires careful study and individual consultation
with the attending physician.