Shallow Water Blackout

By Dr. Duke Scott

Most of us began our diving experience as skin divers…mask, snorkel, fins, a body of water and a curious mind. No fancy equipment or cumbersome tanks were needed. We had total freedom, just another aquatic animal at one with the environment. We quickly learned to suppress our urge to breathe, thereby increasing our maximum time and depth underwater. I have to confess that breath-hold diving is still my favorite diving activity. It gives me a great deal of exercise and requires a considerable amount of skill. I often wonder in this era of high-tech diving, if we as instructors fail to emphasize breath-hold diving to our dive classes? Do we fail to teach the physics and physiology of such diving? Do we offer a thorough explanation of the potential dangers of hyperventilation and the resultant Shallow Water Blackout? In my estimation, we probably do not. Therefore, this article will give you a better understanding of breath-hold diving and its pitfalls.

Breath-holding diving (freediving) is used to describe the activity of skin divers when they hold their breath and dive underwater. The maximum amount of time an individual can hold his breath before safely resuming breathing is called breath-hold time. An individual’s maximum breath-hold time is called the breaking point. Training, motivation and a thorough understanding of the physiology of breath-hold diving increase one’s maximum breath-hold time.

There are anatomical, physiological and psychological factors that determine maximum breath-hold time.

1. Anatomical factors: An individual’s lung volume greatly influences his ability to excel at breath-hold diving. This is genetically determined in each of us and is influenced by environmental factors such as smoking, asthma and chronic lung disease. The healthier the lung means the greater extent for utilizing lung volume.

2. Physiological factors: These factors revolve around the effects of changes in the partial pressure of oxygen (PO2) and carbon dioxide (PCO2) during breath-hold diving. They result from changes in ambient pressure, variations in metabolic rate and differences in gas-perfusion rates of the body’s tissues. The primary stimulus for respiration is increasing PCO2, which stimulates the peripheral chemoreceptors located in the internal carotid arteries (carotid bodies) and in the wall of the aortic arch (aortic bodies). It is also the major stimulus of the chemoreceptors located in the base of the brain (medulla). Decreasing O2 is a secondary stimulus to these chemoreceptors.

3. Psychological factors: The individual’s will and training determine psychological factors. It depends on the diver’s ability to learn to suppress his response to the urge to breathe, or his ability to ignore rising levels of PCO2 in his arterial blood.

When we hold our breath on the surface (1 ATM), several simultaneous factors influence our urge to breathe. Initially, the partial pressure of the alveolar gases will approximately equal air at 1 ATM (PO2 = .21, PN2 = .79, and CO2 = .003). Normal metabolism produces a decrease in PO2 and an increase in PCO2. The volume of O2 consumed essentially equals the volume of CO2 produced. The amount of energy expended by the individual drives the rate of this production. The increasing PCO2 and the decreasing PO2 in the aveolus of the lung and subsequently in the arterial blood determines the breath-hold breaking point. By holding our breath, we allow CO2 to build within our body. The initial values at the onset of breath holding are approximately 40 mmHg for PCO2 and 100 mmHg for PO2. Once the PCO2 in the arterial blood increases to 60 mmHg or the PO2 drops to 30 mmHg, the chemoreceptors become stimulated and the breaking point is reached. But, with dropping PO2 and increasing PCO2 occurring simultaneously, a value of 50 mmHg for both creates a marked urge to breathe. In short, that urge is primarily triggered by hypercapina (elevated levels of CO2) and by hypoxia (decreasing levels of O2). It represents a synergistic relationship.

With this basic understanding of surface breath-hold physiology, we tackle the more complex interactions associated with breath-hold diving. Once the breath-hold diver begins his descent, the increasing ambient pressure compresses the lung and thereby increases the partial pressure of the alveolar gases. These effects are clearly defined by Boyle’s and Dalton’s Laws. The increasing ambient pressure effects the lung by decreasing its volume, as previously discussed. This causes an increase in the partial pressure of the alveolar gases - primarily O2, CO2 and N2. Understanding the effect this has on breath-hold divers is the major concern, so let’s examine the components individually and how they interact.

Increasing CO2 is the main source causing the urge to breathe during descent. With oxygen consumption, there is an equal production of CO2. During breath-hold diving, CO2 builds up, and as the ambient pressure increases, the PCO2 in the aveolus increases to the point that the normal outward perfusion of CO2 is reversed and CO2 is driven into the body’s tissue and fluids. But, because of the increased solubility of CO2 in these tissues, the increase of the PCO2 in the alveolar and the arterial blood is not as great or as rapid as expected. Dr. Suk-Ki Hong showed that during a typical breath-hold dive to 30 feet, the PCO2 increased from 29 mmHg upon leaving the surface to a PCO2 of 42 mmHg on reaching the bottom. This is far below the required PCO2 of 50-60 mmHg needed to trigger the urge-to-breathe mechanism. On the surface the PCO2 increases more rapidly and triggers the mechanism more quickly. As the dive continues and more energy expends, the PCO2 increases. When the breaking point is reached, the diver is alerted to begin his ascent. Once the diver begins his ascent, the ambient pressure decreases. With decompression the lung volume increases and the PCO2 decreases. This initial decrease in PCO2 gives the diver a momentary sense of well being and decreases his sense of urgency to reach the surface. But as the PCO2 perfusion gradient reverses the CO2 flows out of the tissues into the lung and again increases the urge to breathe. Dr. Hong showed that the diver has an average immediate post-dive PCO2 of 42 mmHg. This demonstrates that although the elevated PCO2 alerts the diver to ascend, its influence on his urge to breathe may actually diminish as he rises toward the surface.

The ambient pressure increases with depth. Correspondingly, the PO2 in the aveolus steadily increases with depth. So, although the diver’s oxygen store is consumed by metabolism, this decrease in oxygen is not correctly reflected. The increasing PO2 in the aveolus and therefore in the arterial blood continues to provide adequate oxygenation of the brain and other vital organs as long as the diver remains at depth or deeper. Of course, this depends on the fact that he does not completely deplete his oxygen supply or reach a state of critical hypoxia (PO2 <=.10ATM). The increasing PO2 also suppresses the oxygen component of the urge to breathe. The deeper the diver goes, the greater the arterial PO2 and the longer the urge to breathe are suppressed. This occurs despite the fact our diver is expending a considerable amount of energy and is quickly using his oxygen stores. Dr. Hong showed that during a typical breath-hold dive to 30 feet, the PO2 increases from 120 mmHG to 149 mmHG on reaching the bottom. This is far above the oxygen breath-hold breaking point of 30 mmHG. So, obviously during descent, the PO2 is not a factor in triggering the urge-to-breath mechanism. Upon ascent the ambient pressure steadily decreases. This causes an increase in lung volume and a decrease of the PO2 in the aveolus and arterial blood. Also, our diver continues to consume oxygen. Therefore, as he ascends he develops a progressively sever hypoxia. So, during ascent the PO2 becomes a major factor in the urge-to-breath equation. Our diver should have just enough oxygen to safely reach the surface. Obviously the degree of hypoxia is more profound than experienced during a comparable breath hold on the surface. Therefore, a good rule of thumb is never breath-hold dive longer than you can hold your breath on the surface.

...

Now we have a concept of the forces that interact during a breath-hold dive. The main factor that determines how long an individual can stay underwater is his ability to suppress his response to the PCO2 stimulus to breathe. Fortunately, most of us are not able to suppress that urge long enough to deplete our oxygen to the point of critical hypoxia. This is accomplished by vigorous pre-dive hyperventilation. Almost all breath-hold diving accidents are associated with such hyperventilation and the over-achiever mentality (the individual who always pushes the limits). Hyperventilation increases breath-holding time. During hyperventilation the rate of elimination of CO2 from the body greatly increases, while the amount of O2 in the lung essentially remains unchanged. Therefore, pre-breath-hold hyperventilation greatly reduces the amount of CO2 in the aveolus and the arterial blood. This increases the time before the PCO2 in the blood reaches the breath-hold breaking point. But, this extension of underwater time produces a further reduction of the PO2 in the arterial blood, which reflects the sever reduction in oxygen stores. This endangers one’s safe return to the surface. If the critical state of hypoxia is reached while the diver struggles to reach the surface, he may slip into unconsciousness and drown. Remember that severe hypoxia leading to unconsciousness and/or death can strike without any warning signs or symptoms. This is the Shallow Water Blackout. 

...

Don’ts:
1. Never hyperventilate vigorously prior to breath-hold diving – no more than four slow and controlled breaths.
2. Never breath-hold dive alone.
3. Never exceed your ability, go deeper or stay down longer than your physical condition and training permits.
4. Never practice breath-hold diving in any body of water without a knowledgeable observer.
5. Never perform recreational breath-hold diving after inhaling pure oxygen, Nitrox I or II or any other gas, except air.
6. Never breath-hold dive in cold or murky water without sufficient, prior training.

...

Obtain these and other such data from:
1. Hong, S.K., Cerretelli P., Cruz J.E., Ruhn H.: Mechanics of Respiration During Submersion In Water. J. Appl Physiol 27:537-538, 1969.
2. Blue Water Free Divers: 1-800-667-7462. Freedive! ($45)
3. Local experts: Tec Clark and Glennon Gingo.

PREVENTION OF MIDDLE EAR BAROTRAUMA

If you find the topic interesting, please feel free to save it to a file or print it out for later reference. This document may be reproduced for personal or classroom use but please let readers know where it came from. There is also a video lecture of this material.  Copyright (c) 1997 - 2000 Edmond Kay, M.D.

TABLE OF CONTENTS

• Introduction
• Learning Objectives
• Relevant Anatomy
• What is Ear Fear?
• The Simplest Technique
• Assessing Equalization Efforts
• The Valsalva Maneuver
• The Frenzel Maneuver
• The Toynbee Maneuver
• Beance Tubaire Volontaire (BTV)
• The Roydhouse Maneuver
• The Edmonds Technique
• The Lowry Technique
• The Twitch
• The Take Home Message
• Summary
• Where to Get More Information

INTRODUCTION

Middle ear barotrauma is the most frequent diving injury I see in my medical practice. It occurs much more commonly in the novice diver as a direct result of improper middle ear equalization technique. The following information is intended for the diving instructor, diving safety officer and any individual charged with the responsibility of managing novice divers. This information should also be of value for the advanced or commercial diver interested in rapid descent. The topic includes a discussion of nine different techniques of equalization, and offers tips on assessing the effectiveness of middle ear pressurization.

LEARNING OBJECTIVES

At the end of this topic, the reader should be able to:

1. Define and recognize "Ear Fear".
   
2. Recognize and assess the effectiveness of equalization efforts.
   
3. Discuss the difference between middle ear pressurization and middle ear equalization.
   
4. Describe and be able to teach nine different methods of middle ear equalization.
   
5. Describe the medical conditions that might interfere with adequate middle ear equalization, and understand the appropriate use of decongestants.
   
6. Describe the conditions or injuries that would preclude further diving until medical clearance is obtained.
   

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RELEVANT ANATOMY

The Eustachian tube was first identified by Bartolomeo Eustachio (Latin: Eustachius), an Italian anatomist who died in the 1500's. In the United States the Eustachian tube is usually pronounced "yoo-sta-shan", but some pronounce it "yoo-sta-ke-an" in honor of the anatomist as it more closely approximates the original Latin pronunciation of the name. The tube is approximately 1.5" long and is located in the back of the nasopharynx at approximately nostril level. The tube is normally closed and has a highly variable patency. This means that some individuals will virtually never have problems with middle ear equalization while diving. Others with narrow or partially obstructed Eustachian Tubes may have trouble equalizing their middle ears in airplanes or elevators. These later individuals can dive safely, but for them middle ear pressurization requires meticulous attention to detail and much practice.

Thanks to the comments of Francisco Javier Orellana Ramos, a Diving Medical Officer from Spain, I am reminded that there are several factors that influence tubal patency and tolerance to pressure changes. The Eustachian Tube angle and the shape of the tube can affect ones ability to pressurize the middle ear. Individuals with a relatively large volume of air in the mastoid sinuses will be less tolerant to pressure changes as the actual volume change in the middle ear will be greater for a given amount of descent. Allergies, trauma, infection and Thyroid disorders are other possible causes of disruption in normal tubal function.

For individuals who have difficulty pressurizing ears, the position in the water column is extremely important. It is well known that the head-down position during descent can make middle ear equalization more difficult. Less well understood is the reason for this effect. There are soft tissues in the nasopharynx which surround the membranous Eustachian Tube, and no doubt gravity plays a role in there normal functioning. The most likely candidate for positional obstruction is this soft tissue. A sub-optimal position can compromise marginally patent Eustachian Tube. For this reason it is advisable for students to begin descent slowly, and always in the head up position. Divers with prior ear problems, timid divers and those who are not sure whether middle ears will equalize should also assume this position. Half of the Eustachian Tube is surrounded by bone but the other half is open to the pressure changes of the respiratory system (ambient pressure). This membranous later half is partially surrounded by a "C" shaped cartilage and during swallowing, muscles of the soft palate pull on the Eustachian Tube. This traction opens the tube while closing the nasopharynx. The act of swallowing often causes a clicking or crackling sound to be heard and this sound is the noise made when the moist tissues of the Eustachian Tube pop open. You can hear this sound for yourself in a fellow diver or student by applying a stethoscope in the area around the ear. If the student swallows and the crackling sound is heard, the listener can verify that the Eustachian tube has opened. This technique was first described by Joseph Toynbee in the 1800's, and will be described later.

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WHAT IS "EAR FEAR"?

Ear Fear is a term I have coined to describe the apprehension associated with middle ear equalization. It tends to occur in individuals who have had prior middle ear trauma, a frequent childhood history of middle ear infections or those who just get queasy when they feel new bodily sensations. To some, this sensation of pressure in the middle ears and the crackling in one's head associated with the popping open of a Eustachian tube is uncomfortable. These are the individuals who do not like to "pop" their ears and many have been told all their life that this is "bad to do". For these individuals, middle ear pressurization effort is anxiety provoking and efforts tend to be very cautious and tentative. For many of these novice divers, middle ear trauma occurs at the first dive. Students can become confused about the actual pressure needed to achieve middle ear equalization when well meaning friends remind them not to blow too hard. This advice is certainly prudent when a student is under water and experiencing middle ear squeeze. Unfortunately, for the squeamish individual, and especially if a marginally patent Eustachian tube is present, this limits the ability of some to pressurize adequately at anytime during the dive. Pressurization of the middle ear can and should be vigorous on the surface, when no negative pressure gradient is present across the middle ear. This means that it is possible (and desirable) for an individual to pre-pressurize the middle ear and to inflate the Eustachian tube prior to descent. Pressurization of the middle ear provides a pillow of air behind the tympanic membrane, protecting the "ear drum" (TM) from barotrauma." As descent occurs, more air can easily enter an inflated Eustachian tube and pass into the middle ear, if pressurization begins early in the dive. If the Eustachian tube is allowed to collapse at any time during descent due to squeeze, the pressure to re-inflate it becomes greater. For this reason, I always recommend that individuals practice pressurization of their middle ears prior to diving in order to test their Eustachian tubes for patency, and to perform middle ear pressurization before beginning actual descent to cushion the ears against trauma..

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ASSESSING EQUALIZATION EFFORTS

Before teaching pressurization techniques, it is useful to learn a technique for assessing the adequacy of pressurization. A technique I use in my office is to "watch the nose inflate" (Watch the Schnazolla). Inflation can be observed if one pinches the nasal passages (nares) closed, with pinching fingers held low on the nose. With fingers occluding the nares, observe the fleshy portion of the nose immediately above the fingers. A good, strong pressurization effort will cause the tissues above the occluding fingertips to balloon outward. This nasal inflation is an indication of the inflation effort (nasopharyngeal pressure) that has been applied to the Eustachian tubes. This can be practiced in the mirror in order to optimize technique. Merely pressurizing the nose is not quite the same as inflating the middle ear, but if the diver reports no evidence of a popping or crackling sensation the instructor may check the pressure of the nose to evaluate inflation effort. Practicing on yourself allows some comparisons of effort (and pressure) to be made.

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THE SIMPLEST TECHNIQUE

Among the simplest and most basic techniques in diving are the yawn, swallow, jaw thrust and the head tilt. These techniques of equalizing middle ears are useful for individuals who have widely patent Eustachian tubes and never have problems with equalization. These methods hardly ever work alone without the addition of pressurization in an individual with marginally patent tubes. I do not recommend these techniques for the novice diver as they offer little margin for error. The first dive in a swimming pool is often the cause of significant barotrauma due to a combination of poor technique, student distraction and other factors such as buoyancy control. Pressurization techniques (see below) should ALWAYS be used first, until a student is comfortable with a preferred technique that reliably prevents middle ear squeeze.

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THE VALSALVA MANEUVER (pressurization)

Antonio Valsalva lived in the 1700's and was the first to record a technique for pressurization of the middle ears. With the nostrils pinched closed, pressure is increased in the chest. An attempt is made to blow out the closed nostrils and cheek muscles are kept tight and retracted, not puffed out. With this technique, gradients of 6-10' of seawater can be achieved. This technique does have some disadvantages however as prolonged effort can cause venous engorgement of the tissues around the Eustachian tubes. It also causes a decrease in venous return to the heart and can lower blood pressure if the effort is prolonged. It does seem to be the easiest and most intuitive of the techniques and usually is what a student will perform on their own with no other training.

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THE FRENZEL MANEUVER (preferred pressurization)

Herman Frenzel was a Luftwaffe commander who taught this technique to dive bomber pilots during WW2. The pressure changes in commercial aviation are usually much more gentle and occur more slowly than in diving. A dive-bomber pilot will experience pressure changes more rapidly however, much the same as in diving. The technique developed for flying is to close off the vocal cords, as though you are about to lift a heavy weight. The nostrils are pinched closed and an effort is made to make a "K" or guttural "guh" sound. By doing this you raise the back 1/3 of the tongue and the "Adams Apple" will elevate. For this reason I call the technique the "throat piston". A diver is actually making a piston out of the back of the tongue, pushing it upward. This maneuver compresses air in the back of the throat and the pressurization effort can be seen in the fleshy tissues of the nose. A student may practice the technique by watching the nose inflate and by watching the "Adams Apple" move up and down. Bobbing the "Adams Apple" is good practice for dive-bomber pilots and scuba divers alike. This technique is actually my preferred pressurization maneuver as it can be done anytime during the respiratory cycle and it does not inhibit venous return to the heart. The effort is usually brief and can be repeated may times quickly.

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THE TOYNBEE MANEUVER

Joseph Toynbee lived in the 1800's and as you recall, he first identified the crackling sound present in ones head with the anatomical opening of the Eustachian tube during swallowing. His technique is to pinch nostrils shut while swallowing. The muscles in the back of the throat pull open the Eustachian tube and allow air to equalize if a gradient is present. Swallowing can be difficult for the novice diver, especially while breathing dry air. This technique is not recommended for rapid descent, as there is no margin for error if the Eustachian tube does not equalize on first effort. If a middle ear squeeze is already occurring, it will be more difficult for the Eustachian tube to be pulled open.

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BEANCE TUBAIRE VOLONTAIRE (BTV)

In the 1950's, the French Navy developed a technique for middle ear equalization called "Voluntary Tubal Opening". This technique is difficult to teach and in my hands, only approximately 30% of those taught can perform it reliably. Muscles of the soft palate are contracted while upper throat muscles are employed to pull the Eustachian tube open. This technique is similar to the events that happen in the back of your throat at the end of a yawn. It is also similar to wiggling your ears, and some people seem to be born with the talent, but many cannot master the technique reliably. For commercial divers and dive tenders in Hyperbaric chambers (people who spend many hours in decompression), there is an excellent opportunity to practice the technique while undergoing gradual and predictable pressure changes.

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THE ROYDHOUSE MANEUVER

Noel Roydhouse is a Sports Medicine Physician from New Zealand. He has written an excellent book on the subject, referenced at the end of this article. Some of the most interesting tidbits of information in this section come from his book and I highly recommend it for the reader who just cannot get enough information about the ears. His technique is similar to the Voluntary Tubal Opening except that Dr. Roydhouse has provided an additional clue for contracting the muscles in their proper order in the back of the throat. The instructions are to contract the palate lifters (the levator palatini) and to contract the palate tensor muscles, (tensor palatini). This raises up and tilts forward the uvula. The uvula is the small, fleshy protuberance hanging down from the soft palate in the back of your throat and it can be seen in the mirror. If an individual watches the soft palate and trains the uvula to rise up and tilt forward, half of the technique is mastered. The second part is to tense the muscles of the tongue in such a way as to cause the crackling sensation of Eustachian tube opening to occur. Often a jaw thrust can help make this maneuver more effective, and if the technique for "blowing smoke rings" was ever mastered, this is another good training maneuver which teaches you to recognize the muscles necessary to pull open the Eustachian tube.

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THE EDMONDS TECHNIQUE (pressurization)

Carl Edmonds is an Australian author and lecturer who described a technique where pressurization by either the Valsalva or the Frenzel maneuver can be combined with jaw thrust or head tilt to more effectively open the Eustachian tube. His book (see below) is a must for anyone interested in Diving Medicine.

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THE LOWRY TECHNIQUE (pressurization)

Another combination technique has been described, whereby a pressurization maneuver is combined with a swallow. Coordination and practice is required to pinch nostrils, build up pressure and swallow at the same time but the technique is very effective once it is mastered. Carl Edmonds knows how this technique came about and as soon as he tells me the story I'll update this section. While I have not had that much luck teaching the technique, one of the most respected ENT Physicians in diving medicine, Dr. Alan Decklebaum of San Francisco (now retired) prefers it.

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THE TWITCH (pressurization)

This combination technique is effective for some, and involves pinching nostrils with a moderate pressure in the back of the throat. Generation of pressure is again by either Valsalva or Frenzel Technique. Instead of swallowing as in the Toynbee Maneuver, the head is suddenly "twitched" sideways. Tension in the throat muscles helps to make this a more effective maneuver.

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THE TAKE HOME MESSAGE

Most new divers have trouble with technique, not anatomy or illness. In a very few individuals allergies, acute or chronic infection or nasal polyps may play a role. By far the most common reason for middle ear barotrauma however is inadequate pressurization of the middle ears due to a lack of basic understanding of the mechanisms involved. "Ear Fear" must always be considered as a possible complicating factor and an instructor must be sensitive to the issues surrounding the reluctance of a diver to fully and aggressively pressurize the middle ears. Occasionally a "dragooned diver" will be quite reluctant to learn the techniques of equalization as this may provide a legitimate reason to drop out of the diving. Other phobias may be present such as the fear of water, or confinement fear (claustrophobia). Problems with nasal anatomy such as a deviated nasal septum, intranasal polyps, or obstructed sinuses must be addressed by a medical practitioner and occasionally these will require surgery. Recent advances in endoscopic surgery offer vast improvements over older techniques. There is much that a professional diving safety officer or a good friend can do to help an individual learn safe middle ear equalization practices, but don't forget to look for the obvious. A person with cold symptoms should not dive until the cold has cleared and the Eustachian tube clearly pops with a swallow.

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IN SUMMARY

*  Eustachian tube awareness should be taught to all divers.

*  New divers should always use pressurization to prevent middle ear barotrauma.

*  Watch the tissues of the nose balloon out as inflation pressure increases during pressurization maneuvers.  Assessing the adequacy of inflation effort will help to identify the causes of equalization problems.

*  Listen for the crackle and pop of the Eustachian Tube opening (during swallowing) as this will help train your ears for advanced techniques.

*  Practice bobbing your "Adams Apple" to perfect the Frenzel Maneuver, and teach others this technique.

*  If middle ear barotrauma does occurs, discontinue diving immediately. If symptoms are mild, they should subside within 1-2 weeks. When equalization ability is back to normal, no abnormal sounds or crackles are present in the middle ears and hearing is normal, a diver can return safely to the water. If there is any question, a medical opinion should be obtained.

*  Decongestants never help when cold or trauma symptoms are present, but at the very end of a cold, when just a little minor stuffiness remains, the occasional use of an inhaled decongestant like Afrin (oxymetazalone) spray will do no harm and may help.

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WHERE TO GET MORE INFORMATION

1)  "Underwater Ear And Nose Care", Noel Roydhouse: Best, 1993

2)  "Diving And Subaquatic Medicine", Carl Edmonds: (Third Edition) Butterworth 1992

3)  "Diving Physiology in Plain English", Jolie Bookspan, Ph.D

4)  Divers Alert Network

Return to Doc's Diving Medicine Home Page

Copyright © 2000 Edmond Kay, M.D.
13030 Military Rd. S., Suite 210
Seattle WA 98168
206-242-6500 (Wk)   206-246-7946 (Fx)
Web -- http://faculty.washington.edu/ekay/
Last modified November 4, 2000

Physiology part I


Illustration showing human adaptations to freediving.

As a freediver, your most important asset is your own body. Treated with understanding and respect, your body will transport you to many wonderful adventures underwater. On the other hand, if you ignore the basic rules of physiology or fail to stay in shape, you may suffer serious injury-even death. Adding a dose of common sense to the knowledge you gain from this chapter should help avoid calamity. Although at times these two chapters may sound a bit morbid, keep in mind there are relatively few freediving accidents.
Each dive must be perfect. Once you descend, you're committing yourself to a successful journey back to the surface. Our job in Physiology-part 1 is to help you understand the physiology of breath-holding and relate it to the inherent dangers of freediving. We'll start by addressing the mechanics of respiration, the gases of respiration, the human physiologic adaptations to breath-holding underwater and blackouts. In Physiology-part 2, we'll examine the direct effects of water pressure on your body and gear. This chapter ends with discussions of mental and physical stress, nutrition, heartburn and the effects of temperature.
Respiration
Just as life begins and ends with a breath, so does a freedive. Breathing is such an integral part of life that we take it for granted, but freedivers can't afford to take such a casual approach to respiration.
Respiration is the exchange of gases-oxygen and carbon dioxide-between your lungs and the cells of your body. As you take a breath of fresh air, it warms as it journeys through your mouth and throat and into your lungs. In the lungs, air passes through an ever-smaller network of tubes to end in tiny grape-like sacs called alveoli.........

Middle-ear squeeze
Of the three kinds of ear squeeze-internal, external and middle-ear-it's the middle-ear squeeze that's most common. In fact, it's probably the single biggest cause of freediver dropout. As increasing water pressure forces your eardrums and sinus walls in, you feel pain. If you don't correct this squeeze early in the dive, you may suffer a ruptured eardrum-it's possible to injure yourself in water just 4 feet (1 meter) deep. Unlike scuba divers, who have minutes to equalize their ears and may need to equalize only several times a day, the freediver has just seconds to clear his ears and may need to clear them hundreds of times a day. Because of problems with ear anatomy and/or soft tissue responses to chronic allergy, some individuals will never be able to freedive.
An important segment of your ear-clearing anatomy is the eustachian tube. Its proper function is critical to successful ear clearing. For freediving, the ideal eustachian tube would be a wide-open, straight passage to the ear. Unfortunately, it's neither. Curving upward, this air duct is lined with the same mucous membrane that covers your throat-the very same mucous membrane that swells with allergies or colds. To equalize your ears, you seal your nose by pushing the bottom of the nose pocket against your nostrils (don't pinch) and gently blowing to force air through an open eustachian tube into your middle ear.....................

Inner-ear squeeze
Your inner ear processes vibrations, transmitted through your eardrum, into sound. It also contains your organ of balance. Separating the air-filled middle ear from the fluid-filled inner ear is a thin membrane called the "round window." Rupture of your round window has serious consequences-deafness, debilitating dizziness, nausea and vertigo.
The round window can rupture inward or outward depending on the direction of force applied to it. It ruptures inward when you clear forcefully. Outward rupture occurs when you fail to clear your ears. In an attempt to equalize the pressure gradient between the middle ear and the inner ear, inner-ear fluid breaks the round window and leaks into the middle ear................

Heartburn, or pain in your esophagus, can be a problem for freedivers, especially those prone to this condition. Normally, a valve at the top of the stomach confines the acids of digestion below the esophagus. When these acids leak upward, out of the stomach, they burn the esophagus.
Freediving aggravates this condition for several reasons. Simple immersion increases pressure on the stomach by about four times and distorts the stomach-esophagus valve so that it leaks more easily. The unfavorable effects of gravity when you’re floating or diving downward makes matters worse. Novices, using improper ear-clearing techniques, may swallow air, which also interferes with the stomach-esophagus valve.




GOOD ARTICLES ON STRETCHING:
1. http://www.divefitness.com/html/articles/article_pdfs/should_stretch.pdf
2. http://www.divefitness.com/html/articles/article_pdfs/foot_calf.pdf
3. http://www.divefitness.com/html/articles/article_pdfs/knees_to_neck.pdf
4. http://www.divefitness.com/html/articles/article_pdfs/EAMC.pdf

GOOD ARTICLES ON  NUTRITION

1. http://www.divefitness.com/html/articles/article_pdfs/carbo_role.pdf
2. http://www.divefitness.com/html/articles/article_pdfs/eating_perform.pdf




ON HISTORY OF FREEDIVING
http://www.notanx.com/index_redirect.htm?page=/freediving/history.htm

Title:	FIRST ENTRY OF FIRST BLOG
Date:	2008-01-09 @ 23:41
Security:	public
Mood:	touched

Oscar Peterson