DKW 2 Physiology

7/29/2019 DKW 2 Physiology

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Section Two: Diving Physiology 2

Section Two

Diving PhysiologyHow the human body reacts to the experience of scuba diving is complex and fascinating. Infact, many divers find it the most interesting aspect of diving theory. Certainly, it is one of themost important.

But regardless of the specific mechanisms involved, changes occur to divers because of twovital factors:

1. The mechanical effects on the various air spaces of our body brought about by rapidchanges in pressure. (Sometimes referred to as the direct effects of pressure.)

2. The physiological consequences of breathing gases at higher partial pressures than a

the surface. (Sometimes referred to as the indirect effects of pressure.)The purpose of this section is to help you evaluate your understanding of these phenomena.Without an understanding of these vital concepts, your knowledge of diving theory cannotbe considered complete. In addition, you will find that some of the questions asked in thissection will require an understanding of the concepts introduced in Section One. Therefore, ifit has been a while since you completed Section One, you may wish to briefly review thoseobjectives related to the behavior of gases before proceeding.

Objective 2.1

Identify the substance within the blood that aids in the transport of oxygen, and inwhat component of the blood this substance is contained.

Resources:

Encyclopedia, Chapter Five, under the heading of Blood

Exercises:

1. Oxygen is efficiently transported throughout the body because of a substance called_____________, which is contained in the _____________.

a. oxidative metabolism/bloodb. plasma/arteries

c. protein/heart

d. hemoglobin/red blood cells

RESET


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2-2 Diving Knowledge Workbook

2. If the blood did not contain the substance identified in the above question, blood wouldhave to circulate how many times faster to keep up with the bodys demand for oxygen_____________?

3. Large amounts of carbon dioxide can be carried by the circulatory system back to thelungs for expiration primarily because carbon dioxide:

a. can easily dissolve in the plasma.

b. can easily combine with the hemoglobin.c. can be converted into bicarbonate.

d. is an inert gas like nitrogen.

Objective 2.2

Explain how proper diving techniques and equipment can help avoid exhaustion andexcessive buildup of carbon dioxide.

Resources: Encyclopedia, Chapter Five, under the heading of Responses to Breathing

with Equipment

Exercises:

1. The practice of breathing deeply when scuba diving is important in order to compensatefor the:

a. increased dead-air space resulting from the snorkel or regulator.

b. reduced lung volume resulting from compression of the chest.

c. increased amount of alveolar carbon dioxide.d. All of the above are correct.

2. The practice of breathing slowly when scuba diving is important in order to:

a. minimize resistance caused by turbulence in the airways.

b. compensate for the decrease in energy from immersion in cold water.

c. avoid the potential for thoracic squeeze.

d. All of the above are correct.


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Objective 2.3

Explain the physiological mechanism by which voluntary hyperventilation enables adiver to extend breath-holding time.

Resources:

Encyclopedia, Chapter Five, under the heading of Responses to Breath-Hold Diving

Exercises:

1. When a breath-holding diver submerges in cold water, his heart rate will:

a. increase.

b. decrease.

c. remain unchanged.

d. fluctuate.

2. To reduce the demand for oxygen while breath-hold diving, the diver should:a. breathe pure oxygen before submerging.

b. move slowly and deliberately while underwater.

c. take a few rapid, deep breaths before submerging.


3. To reduce the alveolar carbon dioxide level before a breath-hold dive, the diver should:

a. get plenty of rest.

b. move slowly and deliberately while underwater.

c. take a few rapid, deep breaths before submerging.



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Objective 2.4

Explain the physiological mechanism that causes a shallow-water blackout andwhy this condition usually occurs during ascent rather than descent.

Resources:

Encyclopedia, Chapter Five, under the heading of Hypocapnia

Exercises:

1. The reflex respiratory center regulates breathing based primarily on the level of_____________ in the blood.

a. oxygen

b. nitrogen

c. carbon dioxide

d. All of the above depending upon circumstance.

2. Hypoxia results when the divers carbon dioxide level cannot accumulate to a level highenough to stimulate breathing before the tissues consume the available oxygen.

True False

3. Blackout normally occurs on ascent because:

a. the divers energy expenditure increases.

b. the partial pressure of the alveolar oxygen rapidly decreases.

c. the partial pressure of the alveolar carbon dioxide rapidly decreases.

d. the decreasing pressure causes a carotid sinus reflex.


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Objective 2.5

Explain the physiological mechanism that causes a carotid-sinus reflex, and howthis affects the diver.

Resources:

Encyclopedia, Chapter Five, under the heading of Carotid-Sinus Reflex

Exercises:

1. The carotid-sinus receptors, which are located in the carotid arteries, stimulate the_____________, which is located in the _____________.

a. thyroid/throat

b. cardioinhibitory center/brain

c. S-A node/heart

d. adrenal glands/kidneys

2. The carotid-sinus reflex is caused by an excessively tight

a. exposure suit or boots that constrict the feet.

b. exposure suit that constricts the thorax.

c. exposure suit or hood that constricts the neck.

d. mask strap that constricts the head.

3. When the carotid-sinus receptors detect high pressure, they cause the heart to:

a. slow down.

b. speed up.c. stop momentarily.

d. increase pressure.


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Objective 2.6

Explain the physiological effect of increased carbon monoxide levels (includingcigarette smoking) on the diver and how they can be avoided.

Resources:

Encyclopedia, Chapter Five, under the heading of Carbon Monoxide Poisoning

Exercises:

1. Carbon monoxide is difficult to detect because it:

a. is inert.

b. has a sedating effect on the diver.

c. is odorless and tasteless.


2. Carbon monoxide bonds with hemoglobin over _____________ times more readily thanoxygen can, and takes _____________ for the circulatory system to eliminate it.

a. 200/8-12 hours

b. 100/4-6 hours

c. 50/2-4 hours

d. 20/30 minutes

3. The symptoms of carbon monoxide poisoning are not as noticeable at depth because:

a. high levels of oxygen are dissolved in the plasma allowing tissues to meet their

oxygen requirement.b. high levels of nitrogen sedate the divers central nervous system, slowing his

metabolism.

c. lower levels of carbon dioxide help to counteract the effects of carbon monoxide.

d. lower levels of oxygen make the brain less sensitive and alert.

4. Smoking cigarettes prior to diving can raise the carbon monoxide level _____________times above normal, which in turn _____________.

a. 2/makes it harder to breath

b. 3-12/impairs oxygen transport and carbon dioxide elimination

c. 20-40/increases the risk of a lung-expansion injury

d. 100/increases the risk of heart attack and stroke


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Objective 2.7

Explain the physiological mechanism of decompression sickness (DCS), and list thecommon susceptibility factors that can contribute to its occurrence.

Resources:

Encyclopedia, Chapter Five, under the heading of Inert Gas Absorption

Exercises:

1. If all of our tissues are essentially comprised of water, why dont they all absorb andeliminate nitrogen at about the same rate?

2. Why does DCS occur to recreational divers upon surfacing rather than while they areat depth?

3. Divers succumb to decompression sickness because in humans any amount ofsupersaturation of the tissues with nitrogen will result in significant bubble formation.

True False

4. The various factors that increase the divers susceptibility to decompression sickness relateprimarily to:

a. tissue half-times.

b. physical conditioning.

c. changes to respiration.

d. changes to circulation.


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Objective 2.8

Define the term silent bubbles as it relates to decompression sickness.

Resources:

Encyclopedia, Chapter Five, under the heading of Inert Gas Release

Exercises:

1. The term silent bubbles refers to bubbles that:

a. do not move, such as those that cause decompression sickness in the joints.

b. cannot be heard with any form of electronic sensors.

c. are so small they do not cause signs and symptoms of decompression sickness.

d. appear and disappear very quickly.

2. What is the device used to detect the presence of silent bubbles?

3. Silent bubbles are thought to form because of the presence of:

a. fat particles in the blood stream.

b. impurities in the divers air supply.

c. gas seeds (micronuclei)

d. changes in blood chemistry brought about by high levels of nitrogen.

Objective 2.9

Explain why individuals with decompression sickness (DCS) are given pure oxygenas a first aid measure.

Resources:

Encyclopedia, Chapter Five, under the headings of Inert Gas AbsorptionPhysiological Rationale for First Aid and Treatment of DCS and First Aid andTreatment for Lung Overexpansion Injuries

Exercises:

1. Why does DCS in recreational divers involve nitrogen bubbles but not oxygen bubbles?


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2. Breathing pure oxygen aids the individual with decompression sickness because it:

a. enables the body to metabolize nitrogen more quickly.

b. increases the pressure gradient between the nitrogen pressure in the tissues andthe alveolar nitrogen pressure.

c. decreases the pressure gradient between the nitrogen pressure in the tissues andthe alveolar nitrogen pressure.

d. helps reduce the size of the bubbles.

Objective 2.10

Explain the cause of nitrogen narcosis, state the approximate depth at which thedisorder occurs and list three common signs/symptoms.

Resources:

Encyclopedia, Chapter Five, under the heading of Gas Narcosis

Exercises:

1. It is believed that nitrogen narcosis results from:

a. disruptions in the transmissions between nerve cells.

b. extravascular bubble formation in the brain.

c. a severely decreased sensitivity to pain caused by silent bubbles.

d. mechanisms that are completely unknown to science.

2. The signs and symptoms of nitrogen narcosis normally begin to occur at approximately

what depth?a. 15 metres/50 feet

b. 30 metres/100 feet

c. 45 metres/150 feet

d. 60 metres/200 feet

3. List the three primary signs/symptoms of nitrogen narcosis:

a.

b.

c.


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Objective 2.11

Define the term barotrauma, and explain how it can occur to the lungs, sinuses andears of the diver during both ascent and descent.

Resources:

Encyclopedia, Chapter Five, under the heading of Problems in Body Air Spaces

Exercises:

1. The term barotrauma literally means: ___________________________________________

2. Other than potential damage to the ear drum, an excessively forceful Valsalva maneuvercan result in a(n):

a. oval window rupture

b. round window rupture

c. eustachian tube ruptured. All of the above are correct

3. Severe lung squeeze can occur in shallow depths in which of the following conditions?

a. A skin (breath-hold) diver hyperventilates prior to descent.

b. A scuba diver descends taking excessively large breaths.

c. A skin diver (breath-hold) descends with a normal lung volume.

d. A skin diver descends with his lungs nearly empty.

Objective 2.12Define the term vertigo and explain the mechanism by which this normally occurs in the diver.

Resources:

Encyclopedia, Chapter Five, in the sidebar article entitled Summary of Ear andSinus Barotrauma Treatment

Exercises:

1. Vertigo is a medical term meaning:

a. dizziness.

b. infection of the inner ear.

c. the inability to hear.

d. the ear drum has been ruptured.


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Section Two: Diving Physiology 2-

2. Vertigo can be caused by:

a. ear squeeze.

b. inner ear barotrauma.

c. decompression sickness.


Objective 2.13

Describe the basic anatomy of the ear and which areas/structures are most affectedby changing pressures.

Resources:

Encyclopedia, Chapter Five, under the heading The Ears

Exercises:

1. Sound vibrations are transferred from the outer to the inner ear via the:

a. oval window.

b. round window.

c. cochlea.

d. ossicles.

2. The vestibular canals are located in the_____________ and are responsible for_____________.

a. inner ear/balance

b. middle ear/sound transmission

c. outer ear/channeling sound waves to the ear drum

d. brain/transmitting nerve impulses (sound)

3. Which portion of the ear is most affected by changes in pressure?

a. outer ear

b. middle ear

c. inner ear

d. All areas are equally affected.


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Objective 2.14

Compare and contrast the various signs/symptoms of decompression sickness andair embolism.

Resources:

Encyclopedia, Chapter Five, under the heading Decompression Sickness andLung Overexpansion Injuries

PADI Rescue Diver Manual, Chapter Four, under the heading PressureRelated Injuries

Exercises:

1. A symptom of air embolism may be _____________, while two symptoms ofdecompression sickness may be _____________ and _____________.

a. pain in the joints, fatigue/sudden unconsciousness

b. sudden unconsciousness/pain in the joints and fatiguec. coughing of bloody froth/dizziness and confusion

d. cherry red nail beds/paralysis

2. In terms of the location of symptoms, air embolism is characterized by _____________,while decompression sickness is characterized by _____________.

a. involvement of the head and neck/involvement of the arms and legs

b. involvement of the respiratory center/involvement of the central nervous system

c. involvement of both sides of the body, either upper or lower/involvement of only

one side of the bodyd. involvement of only one side of the body/involvement of both sides of the body,

either upper or lower

3. In terms of the change in symptoms, air embolism is characterized by _____________,while decompression sickness is characterized by _____________.

a. symptoms tending to improve as a result of first aid/usually no change orworsening of condition

b. usually no change or worsening of condition/symptoms tending to improve as aresult of first aid

c. gradual worsening over time/gradual improvement over timed. gradual improvement over time/gradual worsening over time


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Section Two: Diving Physiology 2-

Objective 2.15

State the most serious form of lung-expansion injury in diving and how it occurs, andwhat factors can contribute to its occurrence.

Resources:

Encyclopedia, Chapter Five, under the heading Lung Overexpansion Injuries PADI Rescue Diver Manual, Chapter Four, under the heading Pressure

Related Injuries

Exercises:

1. The most serious form of lung-expansion injury is a(n) _____________ because air bubblesenter the _____________.

a. pneumothorax/thorax

b. pneumothorax/lung tissues

c. air embolism/arterial circulation

d. air embolism/venous circulation

2. Explain how a lung-expansion injury can occur even to a diver who is breathing normally

3. Surfactant is a substance that coats the inner surfaces of the _____________ and helpsprevent them from _____________.

a. bronchioles and alveoli/rupturing

b. bronchioles and alveoli/collapsing

c. veins and arteries/collapsing

d. veins and arteries/rupturing


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Section Two: Answer Key 2-

Correct:ConfidentGuess

Incorrect:

Simple MistakeLack of Knowledge


Incorrect:Simple MistakeLack of Knowledge

Correct:

ConfidentGuess


Section Two

Answer KeyObjective 2.1

Identify the substance within the blood that aids in the transport of oxygen, and inwhat component of the blood this substance is contained.

1. (d)Oxygen is efficiently transported throughout the bodybecause of a substance calledhemoglobin, which iscontained in thered blood cells. Red blood cells whichcomprise 45% of the blood mass contain the proteinhemoglobin. In fact, the chemical reaction between hemoglobin

and oxygen is what makes the cells red. White blood cellsprimarily fight infections. The plasma is the fluid in which all theother components are suspended.

2. If the blood did not contain the substance identified in theabove question, blood would have to circulate how many timesfaster to keep up with the bodys demand for oxygen?15 to 20 times.

3. (c) Large amounts of carbon dioxide can be carried bythe circulatory system back to the lungs for expirationprimarily because carbon dioxide: can be converted

into bicarbonate. Carbon dioxide the waste productof oxidative metabolism is a very reactive compound. Toefficiently transport as much of it as possible back to the lungs,most of it is turned into another compound bicarbonate.Once back at the lungs, the bicarbonate is converted again intocarbon dioxide and released through respiration.


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Objective 2.2

Explain how proper diving techniques and equipment can help avoid exhaustion andexcessive buildup of carbon dioxide.

1. (d) The practice of breathing deeply when scuba divingis important in order to compensate for the:All of the

responses are correct. Deep breathing helps exchangemore air, reducing the effect of increased dead-air spaces. Italso compensates for the reduction in lung volume caused bythe increased pressure on the chest (thorax) due to submersion.Finally, deep breathing helps eliminate the higher than normallevel of carbon dioxide in the alveoli brought about by theincreased resistance of breathing while submerged.

2. (a) The practice of breathing slowly when scuba diving isimportant in order to: minimize resistance caused byturbulence in the airways. Slower breathing reduces thetendency for the air flow to become turbulent. (See figure in

Chapter Five of the Encyclopedia) Turbulence results in increasedresistance and, therefore, an increased breathing effort.

Objective 2.3

Explain the physiological mechanism by which voluntary hyperventilation enables adiver to extend breath-holding time.

1. (b) When a breath-holding diver submerges in cold water, hisheart rate will: decrease.While it is true that if we hold ourbreath on land our heart rate will increase, just the opposite

can occur when we are immersed in water. The phenomenonof decreasing heart rate upon submersion is referred to as themammalian diving reflex. Although humans have far less of aresponse, it is common to all diving mammals. (This accountsfor the incredible breath-hold capabilities of marine mammals.)However, in order for the phenomenon to occur, the face mustbe immersed, or at least moistened, in cold water.

2. (b) To reduce the demand for oxygen while breath-hold diving,the diver should: move slowly and deliberately whileunderwater. This is mere common sense. To reduce thedemand for oxygen, we must reduce our energy expenditure.Breathing pure oxygen prior to diving will, of course, increasethe amount available to us. But, it will do nothing to reduce thedemand. Likewise, hyperventilation will increase our breath-holding capacity by reducing the amount of carbon dioxide,but it will not reduce the demand for oxygen. Only a reductionin work can reduce the demand for oxygen.

Correct:Confident

GuessIncorrect:









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3. (c) To reduce the alveolar carbon dioxide level before abreath-hold dive, the diver should: take a few rapid,deep breaths before submerging.A few deep breathsprior to diving will help flush carbon dioxide out of the lungs.Slow movement will reduce oxygen demand during the dive,but will do nothing to decrease the carbon dioxide levelbefore the dive. Likewise, the amount of rest will have no

impact on reducing the predive level of carbon dioxide. Onlyhyperventilation will do this.

Objective 2.4

Explain the physiological mechanism that causes a shallow-water blackout and whythis condition usually occurs during ascent rather than descent.

1. (c) The reflex respiratory center regulates breathing basedprimarily on the level ofcarbon dioxidein the blood. Aseemingly paradoxical phenomenon is that the factor controllin

the urge to breathe is not primarily the lack of oxygen inour blood. Instead, its an elevated level of carbon dioxide.Incidentally, the noted dive table physiologist J.S. Haldane wasone of the scientists who discovered this fact.

2. Hypoxia results when the divers carbon dioxide level cannotaccumulate to a level high enough to stimulate breathingbefore the tissues consume the available oxygen. True. Thisis precisely why an overextended, breath-holding diver blacksout. Although the tissues are hypoxic in need of oxygen the urge to breathe is suppressed because of the low levelof carbon dioxide influenced by hyperventilation. If the tissuescontinue to be air starved, they begin to cease functioning.Eventually, the breath-hold diver will become unconscious.

3. (b) Blackout normally occurs on ascent because: the partialpressure of the alveolar oxygen rapidly decreases.At depth, the elevated partial pressure of alveolar oxygen canbe sufficient to meet the tissues demand. However, when thediver ascends, the oxygen partial pressure quickly drops (Forexample, an ascent from 10 metres/33 feet will result in areduction of the partial pressure by 50%). Now, suppose thediver barely had enough oxygen at depth to remain conscious

and functional. A severe drop would be enough to decreasethe level to a point the body could not tolerate. So, although thdiver could continue to function at depth, he will black out as heascends to the surface due to the abrupt decrease in the oxygepartial pressure.










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Correct:Confident

GuessIncorrect:




Objective 2.5

Explain the physiological mechanism that causes a carotid-sinus reflex, and how thisaffects the diver.

1. (b) The carotid-sinus receptors, which are located in the carotidarteries, stimulate thecardioinhibitory center,which is

located in thebrain. Although the impulse that simulates theheart originates in the heart (sino-arterial node), the brain hasthe capability to inhibit this impulse. This is what occurs in acarotid-sinus reflex. The heart rate slows down to a point whereit is unable to maintain sufficient blood flow to the brain.

2. (c) The carotid-sinus reflex is caused by an excessively tight:exposure suit or hood that constricts the neck.Because the receptors are in the carotid arteries (neck),anything constricting that area could cause the reflex to occur.Dry suit neck seals are particularly noted for this.

3. (a) When the carotid-sinus receptors detect high pressure, theycause the heart to: slow down. In essence, the brain is fooled.The pressure the receptors are sensing results from the squeeze ofthe hood or exposure suit, not the pressure within the artery.

Objective 2.6

Explain the physiological effect of increased carbon monoxide levels (includingcigarette smoking) on the diver and how they can be avoided.

1. (c) Carbon monoxide is difficult to detect because it: isodorless and tasteless.People mistakenly believe thatcarbon monoxide smells like car exhaust. This is not the case.The smell given off from internal combustion engines resultsfrom hydrocarbon emissions. Carbon monoxide itself has noodor. Although a diver will eventually become unconscious, thisis not because of any sedative effect, but rather due to hypoxia.

Clearly, carbon monoxide is not inert (chemically inactive).




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Correct:

ConfidentGuess

Incorrect:


2. (a) Carbon monoxide bonds with hemoglobin over200timesmore readily than oxygen can, and takes 8-12 hoursfor thecirculatory system to eliminate it. The molecular structure of carbomonoxide enables it to combine with hemoglobin more readilythan can oxygen 200 times more readily. In fact, the bondingof carbon monoxide and hemoglobin is so strong that it takes oveight hours for it to be released from the bloodstream.

3. (a) The symptoms of carbon monoxide poisoning are not asnoticeable at depth because: high levels of oxygen aredissolved in the plasma allowing tissues to meet theiroxygen requirement. Remember that tissues receive oxygenin two ways. Primarily they are supplied by oxygen carried bythe hemoglobin. But, they are also supplied by free oxygendissolved in plasma. With the increased partial pressure at depththe amount of oxygen in solution could be sufficient to providethe tissues demand. The carbon monoxide would then have nonoticeable effect. However, as the partial pressure drops duringascent, the oxygen in the hemoglobin will be needed. However,

the hemoglobin is locked-upby carbon monoxide, then insufficieoxygen will be delivered to the tissues.

4. (b) Smoking cigarettes prior to diving can raise the carbonmonoxide level3-12times above normal, which in turn impairoxygen transport and carbon dioxide elimination.One of the primary by-products of burning tobacco is carbonmonoxide. Once in the bloodstream it combines with thehemoglobin, effectively locking out the oxygen. In addition,because hemoglobin also transports carbon dioxide on its returnto the lungs, it also hinders the transport of this gas. The evidence

for not smoking is overwhelming for anyone. For divers even moso. Dont smoke, particularly if you are a diver!

Objective 2.7

Explain the physiological mechanism of decompression sickness (DCS), and list thecommon susceptibility factors that can contribute to its occurrence.

1. If all of our tissues are essentially comprised of water, why dontthey all absorb and eliminate nitrogen at about the same rate?Although our tissues are comprised primarily of water, there are som

important differences among tissues that affect their gas absorptioncharacteristics. First, tissues have differing densities. Bone, foexample, is more dense than skin. This will affect how gas is diffuseonce it reaches the tissue. Secondly, the blood supply differsamong tissues. Therefore, tissues receiving more blood supply whave more gas delivered and eliminated.

Correct:

ConfidentGuess

Incorrect:


Correct:

ConfidentGuess

Incorrect:


Correct:

ConfidentGuess

Incorrect:



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2. Why does DCS occu r to recreational divers upon surfacingrather than while they are at depth?Bubble formationcannot occur until the tissues become supersaturated(ie. hold more gas than the ambient pressure).Supersaturation cannot occur, however, until theambient pressure is reduced upon ascent. As saturationdivers have shown us, humans can remain at depth indefinitely

and not get DCS. The problem occurs only when we ascend.3. Divers succumb to decompression sickness because in humans

any amount of supersaturation of the tissues with nitrogen willresult in significant bubble formation. False. Humans cantolerate some degree of supersaturation. Otherwise, we wouldget the bends by merely going to the top of a skyscraper inan elevator, or driving up a mountain. The important factor isdetermining how much supersaturation can be tolerated withoutthe formation of nitrogen bubbles. This is what decompressionmodels seek to explain.

4. (d) The various factors that increase the divers susceptibilityto decompression sickness relate primarily to: changes tocirculation. Two factors affect gas absorption the densityof the tissues and the blood flow. We can help control only oneof these the amount of blood flow (circulation) getting to thetissues. In reviewing the various susceptibility factors, noticehow most involve (to some degree) circulation: 1) decreasedcirculation efficiency with age; 2) increased circulation fromexercise; 3) changes in circulation during alcohol consumptionand 4) recent illness/injury. The only factor that takes tissuedensity in consideration is obesity. And it is unclear as to what

effect this really has upon recreational divers.

Objective 2.8

Define the term silent bubbles as it relates to decompression sickness (DCS).

1. (c) The term silent bubbles refers to bubbles that: are sosmall they do not cause signs and symptoms ofdecompression sickness. The term silent simply refers tothe fact that the bubbles are so small that they apparently causeno symptoms of DCS. It has nothing to do with the ability todetect them.








Incorrect:



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2. Silent bubbles can, in fact, be detected using ultrasoundtechnology. A pre-cordial Doppler Ultrasound Flowmetercan enable scientists to hear the silent bubbles as they travelto the lungs in the venous circulation. This phenomena is usedas a criterion in testing decompression models and some divetables/computers.

3. (c) Silent bubbles are thought to form because of the presence

of: gas seeds (micronuclei). Just as rain drops requiredust particles on which to form, it is theorized that nitrogenbubbles need some form of seed. These seeds are termedgas micronuclei - unwettable microscopic gas pockets on tissuesurfaces that act as seeds for bubble growth.

Objective 2.9

Explain why individuals with decompression sickness (DCS) are given pure oxygen asa first aid measure.

1.Why does DCS in recreational divers involve nitrogen bubblesbut not oxygen bubbles?Nitrogen is physiologicallyinert, meaning that it is not used in the metabolicprocess. Therefore, whatever nitrogen is absorbedby the body as the ambient pressure increases mustbe eliminated as the ambient pressure is reduced. Indecompression sickness, bubbles form because thenitrogen cannot escape quickly enough to remainin solution. Oxygen bubbles do not form becausethe oxygen we breathe is used up in the metabolicprocess.

2. (b) Breathing pure oxygen aids the individual withdecompression sickness because it: increases the pressuregradient between the nitrogen pressure in thetissues and the alveolar nitrogen pressure.From ourdiscussion of diving physics you should remember that thedifference in the pressure within a liquid (gas tension) and thegas in contact with it is referred to as the pressure gradient.

When this condition occurs, the gas within the liquid and that icontact with the liquid will attempt to equalize. A large pressuregradient is said to create a high driving force, meaning the gasexchange will take place rapidly. In decompression sickness thetissues of the body contain a high level of nitrogen. The alveolaair also has nitrogen within it, but less than what is within the










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tissues. As a result, there is a pressure gradient between thenitrogen in the tissues (high) and the nitrogen within the alveolarair (low). Hence, the nitrogen begins to come out. But, if insteadof air the diver breathes oxygen, there will be no or verylittle alveolar nitrogen. This will further increase the pressuregradient between the tissue nitrogen levels and the alveolarnitrogen levels. The result is a significant increase in the drivingforce of the tissue nitrogen, thus aiding in its elimination.

Objective 2.10

Explain the cause of nitrogen narcosis, state the approximate depth at which thedisorder occurs and list three common signs/symptoms.

1. (a) It is believed that nitrogen narcosis results from:disruptions in the transmissions between nerve cells.Though not fully understood, it is believed that nitrogen narcosisresults from disruptions in nerve impulse transmissions. Inertgases particularly when breathed under pressure have the

capacity to cause this disruption. The degree of the disruptiondepends upon how well the gas dissolves into the lipid (fat)tissues. As we are all aware, nitrogen has no effect at surfacepressure. But, when breathed under sufficient pressure, it toocan cause the disruption of nerve impulse transmissions.

2. (b) The signs and symptoms of nitrogen narcosis normally beginto occur at approximately what depth?30 metres/100 feet.In most people the signs/symptoms of nitrogen narcosis willbegin to appear at approximately 30 metres/100 feet. However,this is a highly individual consideration. Many divers have

succumbed to the disorder at much shallower depths, particularlyin instances where drugs or alcohol have been consumed.

3. List the three primary signs/symptoms of nitrogen narcosis:a) poor judgment; b) decreased coordination; and c)a feeling of false security. Other signs/symptoms includefoolish behavior, anxious or uncomfortable feelings and ageneral disregard for safety.


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Objective 2.11

Define the term barotrauma, and explain how it can occur to the lungs, sinuses andears of the diver during both ascent and descent.

1. The term barotrauma literally means: pressure injury(baro = pressure, trauma = injury).

2. (b) Other than potential damage to the ear drum, an excessivelyforceful Valsalva maneuver can result in a(n): round windowrupture. During an excessively forceful Valsalva maneuver,increased pressure in the chest inhibits the flow of blood returninto the heart. As the venous blood backs up it momentarily raisethe pressure of the cerebrospinal fluid. (Its the job of the venouscirculation to absorb this fluid that bathes the nerves.) As thecerebrospinal fluid includes the perilymph within the inner ear,the pressure within the inner ear rises. This rise in pressure causethe round window to bulge outward. If the pressure continues tobuild, the bulge can grow to a point where rupture will occur. Th

is a primary reason why divers are warned to be cautious whenclearing their ears using the valsalva maneuver.

3. (d) Severe lung squeeze can occur in shallow depths in which ofthe following conditions?A skin diver descends with hislungs nearly empty. Although rare, thoracic squeeze canbe life threatening. The mechanics are easy to understand if youthink back to our discussion on diving physics. An expandablecontainer like our lungs when taken to depth will besqueezedby the pressure, resulting in a decrease in volume.If the container (lung) is full, the descent will merely reduce its

volume. However, our lungs cannot be reduced below their emp(residual) volume without the potential for damage. Therefore, if rapid descent is begun after a forceful exhalation, a reduction inlung volume below the residual level will rapidly occur. This couldresult in severe tissue damage and bleeding.

Correct:Confident

GuessIncorrect:







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Objective 2.12

Define the term vertigo and explain the mechanism by which this normally occurs inthe diver.

1. (a) Vertigo is a medical term meaning: dizziness. Vertigois defined as a disoriented state where the individual has the

feeling of rotating or spinning.2. (d) Vertigo can be caused by:All of the responses are

correct. Various forms of ear squeeze can cause vertigo.Examples are: cold water entering the middle ear as a result of aruptured ear drum; and a reverse block in one of the eustachiantubes allowing one ear to depressurize on ascent but not the other.As the sense of balance is controlled by the inner ear, damage tothis organ usually results in some form of vertigo. Finally, in rarebut severe cases, bubble formation from decompression sicknesscan occur in the inner ear and result in vertigo.

Objective 2.13

Describe the basic anatomy of the ear and which areas/structures are most affectedby changing pressures.

1. (d) Sound vibrations are transferred from the outer to the innerear via the: ossicles. The ossicles are the series of bonesthat are attached at one end to the tympanic membrane (eardrum) of the outer ear, and are connected to the oval window

of the inner ear. The mechanical advantage resulting from thearrangement of the ossicles also amplifies the vibrations as theypass from the outer to the inner ear.

2. (a) The vestibular canals are located in theinner earand areresponsible forbalance. In addition to enabling us to hear, theinner ear also controls the sense of balance via the vestibular orsemi-circular canals. These canals are arranged in such a waythat the movement of fluid within them can be interpreted by thebrain to determine balance and orientation.

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3. (b) Which portion of the ear is most affected by changesin pressure?middle ear. The outer ear structures (canal,lobes) are open to the water, and are unaffected by changesin ambient pressure. Like any air-filled structure of the body,the middle ear is affected by changes in ambient pressure.Although what occurs in the middle ear can, in turn, affectthe inner ear, the inner ear itself is not directly affected by thechange in ambient pressure because it is fluid-filled.

Objective 2.14

Compare and contrast the various signs/symptoms of decompression sickness andair embolism.

1. (b) A symptom of air embolism may besuddenunconsciousness,while two symptoms of decompressionsickness may bepain in the jointsandfatigue. In airembolism, air bubbles escape directly into the pulmonary vein,are transported to the heart and then most likely to the

brain. The bubbles begin to expand upon ascent and eventuallyblock arterial circulation when they become too large to passthrough the blood vessels. Much like a stroke, this blockagecuts off vital blood flow to the brain, usually resulting in almostimmediate unconsciousness. Coughing of bloody froth is actuallynot a very common sign. On the other hand, decompressionsickness results from nitrogen elimination occurring so quickly due to a reduction in ambient pressure that it comes outof solution and forms bubbles. This condition does not occurimmediately, but rather over time (taking usually 30 minutes ormore). Although not fully understood, many believe that joint pai

is a result of extravascular bubble formation in the ligaments andtendons of the joints.

2. (d) In terms of the location of symptoms, air embolism ischaracterized byinvolvement of only one side of thebody, while decompression sickness is characterized byinvolvement of both sides of the body, either upperor lower. Air embolism often resembles a stroke the entireright or left side of the body is affected, according to whicheveside of the brain is involved. (The right brain controls the motorcoordination of left side of the body and vice versa). Therefore,

symptoms of air embolism appear likewise. In decompressionsickness, particularly when it involves the central nervoussystem, the symptoms are more akin to paralysis. In this caseboth sides of the body upper or lower are affected,according to where in the spinal column the bubble damagehas occurred.




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3. (a) In terms of the change in symptoms, air embolism ischaracterized bysymptoms tending to improve asa result of first aid,while decompression sickness ischaracterized byusually no change or worsening ofcondition. In cases of embolism, a victim will often appear toimprove once they are treated for shock and begin breathingpure oxygen. In cases of decompression sickness, the conditionrequires time to develop and, therefore, requires time andaggressive treatment to improve. Immediate first aid measureswill tend to have little consequence on bubble growth. Symptomswill often not show improvement as a result of first aid.

Objective 2.15

State the most serious form of lung-expansion injury in diving and how it occurs, andwhat factors can contribute to its occurrence.

1. (c) The most serious form of lung-expansion injury is a(n)air embolismbecause air bubbles enter thearterial

circulation. Although all forms of lung-expansion injury areserious, air embolism is clearly the most serious. In this case,air bubbles enter the arterial circulation and similar to astroke block blood flow. To make matters worse, the bubblesusually migrate to the brain; and in accordance with the lawsof physics, the bubbles continue to expand as long as thediver ascends. No other lung-expansion problem has suchimmediately life-threatening consequences.

2. Explain how a lung-expansion injury can occur even toa diver who is breathing normally. Any obstruction that

prevents the normal release of air from the lungs can causeoverpressurization. These obstructions can occur for variousreasons. Even though the diver may breathe normally,obstructions deep in the lungs may not allow air to escape.Various diseases such as asthma and other pulmonary disorderscan cause these obstructions. However, a more prevalent causeof lung obstructions in divers are those resulting from smokingcigarettes, or diving after a severe chest cold.

3. (b) Surfactant is a substance that coats the inner surfaces ofthebronchioles and alveoliand helps prevent them fromcollapsing. Because of the size and flexibility of the structuresof the lungs, the bronchioles and alveoli tend to collapse uponexhalation. To prevent these structures from remaining shutonce they collapse, the walls of the bronchioles and alveoli arecoated with a chemical referred to as a surfactant. Still anotherdanger of cigarette smoking is that it destroys the surfactant,inhibiting the reopening of the bronchioles and alveoli.





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Section AnalysisFrom the answer key, identify any items marked "correct-guess" or "incorrect-lack ofknowledge." These items represent important points of information or concepts you still might

not fully understand. Check below any objectives that contained items with a "correct-guess"or "incorrect-lack of knowledge" response. Completing this section is an important step indetermining your understanding of physiology as it relates to recreational diving.

Confident Guess Total

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Simple Mistake Lack of Knowledge Total

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Objectives To Be Reviewed:

2.1 2.2 2.3 2.4 2.5

2.6 2.7 2.8 2.9 2.10

2.11 2.12 2.13 2.14 2.15

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DKW 2 Physiology