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BENDS EXPLAINED

iUniverse, Inc.

Chapter One

The first requirement for bends to occur is that the diver has to have been breathing a gas that can cause bends, namely nitrogen, under greater pressure than ambient pressure for some time to allow for on-gassing of the tissue (for the tissue to absorb the nitrogen). There has to be some history of a long dive under a substantial amount of pressure or depth. Repetitive dives, more than one a day, or flying (reducing the ambient pressure) are the culprits most often responsible for bends. Deep dives on air have other limiting physiological consequences such as blindness under pressure, increased viscosity of the pressurized air as well as regulator problems interfering with breathing. Increased partial pressures of oxygen constrict the blood vessels nourishing the retina, as well as vessels in the heart and brain. The visual field is narrowed and then disappears at great depths breathing air or another air and nitrogen mix. Nitrogen interferes with sight under high pressures also. Tissue oxygen tension may be directly measured. Tissue nitrogen concentrations are calculated, measured indirectly.

There is usually a history of extreme exertion before, during or after the dive. Other events sometimes noted are rapid ascent, extreme cold, unusual warm temperature, and past surgery at the point of symptoms. In the patient's history, it is often noted that they were aware that something was going on, but the significance of the sensation was not appreciated and it was not considered a bends symptom. Almost always someone other than the diver has helped (or insisted that) the diver request an evaluation for the need for a chamber treatment. Divers show "la belle indifference" or denial of the realization that their internal milieu has changed and that they have gotten bent.

The term "bends" derives from a condition that tunnel workers developed while working 12 hour shifts at 60 fsw; 60fsw multiplied by 0.445 lbs/sq inch/foot of sea water (1.46 lbs/sq in/meter of sea water) or 26.7psi gauge approximates the working pressure of air compressors during the 1860's. Their extremities would be fixed in position and could not be straightened due to bubbles destroying the bone in shoulder, knee, and other joints

Most divers and many insurance companies I have dealt with expect that the diver will know that bends has occurred if there is an ictus such as paralysis of an extremity or sudden blindness on ascent to the surface. Often, if a diver is limping on arrival at the dive boat, it is passed off as a swimmer's cramp, a weight belt shifted and bruised a muscle, or fatigue. The diver may just stand around for a while before taking off their gear, which includes 35 pounds of scrap metal called a SCUBA tank, a twelve pound or more weight belt to compensate for the buoyant wet suit and the buoyancy of the empty air tank, assorted tools, knives, gauges, harnesses, buoyancy compensating vest, et cetera. The buddy's responsibility is to note if the affected diver sort of collapses on sitting down. A diver rarely says that he/she cannot work today despite glassy eyes, inability to concentrate and focus their attention.

An interested observer may only be looking for focal weakness of an extremity and does not grasp the significance of the complaint that concentration on a task is impossible. A diver may complain of pain. Pain is a type one bends complaint and could be ascribed to a muscle pull. Neurological complaints of weakness are considered bends type two. Inability to pay attention and recite their name, address, phone number, date of birth, birth place, and the number of their favorite credit card may not even be assessed. It would be a type two cerebral symptom. Inability to wake up, speak, stand, or answer are more serious bends symptoms that may be due to a subdural hematoma or other injury. Observed bruises and tenderness on deep palpation may suggest a broken bone or organ rupture.

Pneumothorax may be difficult to diagnose right after a dive and should always be considered if the diver has any impairment. I have seen divers who had active pneumonia diagnosed after they went diving. This is a risk factor for pneumothorax and bacterial or air embolism. Divers tend to pass off or rationalize pain as a sprain. I cannot remember any diver that told me that they were off the no-decompression limit of the dive table that they were using. Unfortunately, many divers only learn how to use the tables after they have symptoms of bends, and then they often alter their logs to be in compliance with the tables. Divers try to justify by shaving their depths and times that they were in the safe table limits considering the decompression stops they were supposed to take on ascent. They may count 75fsw as 70 fsw because they were at 70 fsw most of the time.

With a buoyant tank on your back and without an extra six pounds of weight on your belt, decompression stops are impossible to take. Holding onto an anchor line converts the hypotenuse described by the line to the y axis. Straightening the anchor line to a bottom-to-surface line because of your buoyancy is what actually happens. A separate decompression line with a float is better. However, the current also "hypotenuses" (my term, not in Webster's Dictionary) the decompression line. A portable chamber, such as the FlexiLite®, is safer and more affordable than an emergency helicopter evacuation. Sometimes, evacuations are impossible to arrange in an emergency because of lack of personnel, a holiday or an equipment malfunction. The chamber they are transported to may not be operational due to lack of tenders or oxygen, failed compressor or loss of electricity due to weather conditions.

If the diver arrives at the treatment facility alone, the buddy, who is usually not bent (often because they dove fewer dives that day or they did not dive the day before) will have the usual comments. Buddies tend to support the injured diver's claim that the limits and decompression/no decompression schedule were respected. Most aquanauts did not read my book and do not have enough understanding of bends to appreciate what is going on and how to avoid bends. I have offered to teach bends subjects at dive shops that certify divers. They decline the offer because this type of instruction would point out that there is risk to Self Contained Underwater Breathing Apparatus (SCUBA) diving. The term SCUBA should alert the customer that you need to understand a gadget which enables you to breathe underwater because your mother was not a fish.

SCUBA diving is less risky than snow skiing. I have heard that comparison and state that any sport has some risk and risks can be managed. Health evaluation, instruction, and following rules are effective ways to manage the risks associated with participating in sports. With millions of divers getting certified each year accidents or mishaps crippling and killing divers can and do happen.

Too often the profile of the dive is set by the depth of the water. Take the Blue Hole at Belize, for example. A first open water dive at 135 fsw is not planned for (ten minutes for a single decompression dive), but the ledge at that depth and the one at 170 fsw are macho goals. I would not fly home the day after that dive, but some people do. The physical required for sport diving is not designed to detect problems with the diver's psychological reactions to accident scenarios.

The medical release to be fit to dive does not include a qualifying statement that some medical problems that may become a hazard in the water are not detectable by the required examination. I have refused to sign a fit-to-dive slip for a diver with a seizure disorder only to have that diver return later with an explanation that he recently had a seizure while diving. I have heard that it is acceptable practice to allow asthmatics to dive, even with a history of exercise induced asthma; that it is the diver's right to dive if they want to; and it is the diver's right to breathe any mixture of gasses that they want to breathe during their dive.

On the ascent, blood (which is considered a tissue) and other tissues are always supersaturated with the gasses used in the breathing mixture. Astronauts breathe oxygen for hours before a launch into space in order to off-gas the nitrogen already in their tissues to prevent bends. Bends has also been noted after space walks, long duration plane flights at extremely high altitudes, and after prolonged underwater habitat stays at shallow depths, less than 10 meters, for weeks.

There is often a delay from the ascent until the appearance of bends symptoms. Initially bubble niduses form and grow. Cavitation, a normal result of joint motion, sucks dissolved air into low pressure areas of the joint space. Bubbles form and mechanical effects cause pain, reduce oxygenation of the bone and with time, destroys the integrity of the joint. If the bubble nidus does not grow it disappears because its surface tension is very large. Bernoulli, a mathematician and friend of J.S. Bach, proved the simple relationship T, surface tension, = p, pressure in the bubble, divided by r, the radius of the bubble. When the T is large because the radius is very small, the bubble cannot exist. If the bubble is large, it stays. Breathing oxygen helps get nitrogen out of the bubble by equilibrating the composition of the oxygen in the bubble with the oxygen in the blood and tissue. Nitrogen diffuses out during the equilibrating process. Metabolism of the oxygen shrinks the bubble causing an increase in the surface tension, and thus the demise of the bubble. This dance of gasses in and out of the bubble is referred to as the oxygen window. If a denatured layer of proteins forms on the surface of the bubble, nitrogen dancing outside the bubble is prevented mechanically.

Bends symptoms are thought to be caused by direct pressure on a nerve ending by enlarging bubbles. The bubbles also interfere with blood flow necessary for oxygenation of the tissues. Anoxia also causes pain. Bubbles may be solitary fellows as sometimes seen in a retinal vessel, or appear as pearls on a string. The retinal blood vessel outline has a round clear bulge with a red line on both sides of it. Bubbles may be elongated, filling the blood vessel for a length of a few centimeters and the bubbles in a large artery may resemble the foam which comes out of a soap dispenser. If two nerves are involved, the brain only pays attention to the one in greater pain. When that bubble resolves, then attention is directed to the lesser pain. It is as if the original bubble causing the pain moved over to the remaining bubble's location.

Bends sites may be multiple, but only the most painful is noticed. For example, if you are stuck simultaneously with two pins, you'll only feel the more painful one. You unconsciously extinguish the sensation of the lighter one. However, when you get relief of the more painful site, then you notice the other one. Thus treatment for bends can make you "worse" than you were originally. Sometimes, it is convenient to explain to the patient that it is as if the bubble moved to another site.

Bubbles can act as a foreign body and denature the protein surrounding them. This is akin to what happens to an egg when it is cooked. On the one hand, the denatured protein shrinks as a scar does, so even a late treatment is often effective. Any treatment helps partially injured tissue to recover. On the other hand, the tissue may have been cooked to a point where it will not recover. This happens when the insults to the tissue are many over a long period of time as occurs in commercial fishermen who dive six tanks a day to a hundred feet or more on each dive. Hydration and rest after a day of this type of diving is not good enough. Surface-On-Deck decompression breathing oxygen, usually at forty fsw, for a couple of hours prevents bends after repetitive dives.

Nitrogen is orders of magnitude more soluble in fatty tissue than in muscle or blood. Nerves, spinal cord, and the brain are fatty tissues. The omentum and subcutaneous fat are a couple of the body's storage tanks for nitrogen. Long treatments are needed to off-gas the nitrogen from these storage depots as well as the nervous system's tissues. Short treatments favor redistribution of nitrogen from fat to nervous system tissues. Treatment past the point of relief is the rationale for completing the table selected at the beginning, when the profile is analyzed.

Complement is a substance necessary for red cell agglutination to take place. Divers who go diving frequently get acclimated. One of the measures of acclimation is reduction of the amount of circulating complement. The explanation is that blood coagulation cascade proteins get denatured by subclinical bubbles. Some of these proteins are complement. Less agglutination means less impediment to blood flow which off gasses the tissues. Acclimated divers have fewer incidences of clinical bends for this reason. Capillary beds vary and some divers are less prone to bends than others are.

Acclimation of the diver's chemistry and physical attributes, e.g. muscular conditioning, wards off the bends. Lack of physical conditioning when diving can be disastrous for many reasons, including thrombo-embolism, early exhaustion, cardiac arrhythmia, hyperventiliation and no physical reserve necessary for the physical demands of the dive plan.

Chapter Two

NITROGEN NARCOSIS

Various gasses have pharmacologic properties when inhaled under pressure, in a pressurized environment. Air has 78% nitrogen which is inert. Air also has 21% oxygen which reacts with almost everything except gold and argon, another inert gas. Diving deeper or pressure greater than two ATA, atmospheres absolute or 33 fsw, there begins a narcosis (sleepiness) and at three ATA it is referred to as "Martini's Rule." The diver behaves as though he/she drank a few martinis which consist of a glass containing 2 or 3 ounces of 50% ethanol with a few drops of sweet vermouth and perhaps an olive or small onion for flavor.

Diving deeper than four ATA, while breathing compressed air causes confusion and constriction of the visual field, which progresses to tunnel vision and reversible blindness. This occurs without warning, making it difficult to ascertain if you are going up or down. Deeper than seven ATA (33+2x99fsw=231fsw) oxygen toxicity and seizures are inevitable. During an oxygen seizure, the regulator is expelled from the mouth by the tongue. The drowning victim is recovered and is thought to have given the regulator to a fish, part of the Martini's Rule hype. Oxygen seizures can occur at shallower depths even in acclimated and experienced divers. Anyone could have a fit at any time; it is predictable only in its unpredictability. Fortunately, most people do not have them.

Electroencephalograms (EEGs) can indicate if there is a seizure focus in someone who has had fits recently. But the EEG is not a screening tool to predict a tendency to oxygen seizures at depths greater than three ATA. It has been standard operating procedure in some circles to subject the diver to three ATA and breathing pure oxygen for periods of 20 to 80 minutes to see if they are seizure prone. They could have a seizure as well as a persistent postictal focal weakness after this exercise, which would make them unqualified for deep diving and other occupations where they would be respiring oxygen for hours at a time. However, if the weakness did not clear up they would be disabled for many other types of work also. If testing can cause disability, imagine what repetitive deep diving can do!

Weightless Environment

Adjustment of buoyancy allows the diver relative freedom from the tug of gravity and allows ease of movement in three dimensions.

(Continues...)

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Excerpted from BENDS EXPLAINED by JEFFREY H. RUDELL Copyright © 2009 by JEFFREY H. RUDELL, MD. Excerpted by permission of iUniverse, Inc.. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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