EFFECTS OF BAROTRAUMA AND PRESSURE ON THE HUMAN BODY
The tissues of the body can withstand tremendous pressure. Divers have made
open-sea dives in excess of 1,000 fsw (445 psi) and, in experimental situations,
have been exposed to a depth of 2,250 fsw (1001.3 psi). Despite these pressures, it
is somewhat ironic that divers make the greatest number of medical complaints during the shallowest part of a dive. The cause is barotrauma, which is the damage
done to tissues when there is a change in ambient pressure. Barotrauma on descent
is called squeeze. Barotrauma on ascent is called reverse squeeze.
Conditions Leading to Barotrauma
Barotrauma does not normally occur in
divers who have normal anatomy and physiology, and who are using properly
functioning equipment and correct diving procedures. Barotrauma can occur in
body areas subject to all five of the following conditions:
- There must be a gas-filled space. Any gas-filled space within the body (such
as a sinus cavity) or next to the body (such as a face mask) can damage the
body tissues when the gas volume changes because of increased pressure.
- The space must have rigid walls. When the walls are elastic like a balloon,
there is no damage done by gas compression or expansion until the volume
change surpasses the elasticity of the walls or vessels.
- The space must be enclosed. If any substance (with the exception of blood in
the vessels lining the space) were allowed to enter or leave the space as the gas
volume changes, no damage would occur.
- The space must have vascular penetration (arteries and veins) and a membrane
lining the space. This allows the blood to be forced into the space and exceed
the elasticity of the vessels to compensate for the change in pressure.
- There must be a change in ambient pressure.
Overpressure is caused when gas
is trapped within the sinus cavity. A fold in the sinus-lining membrane, a cyst, or
an outgrowth of the sinus membrane (polyp) may act as a check valve and prevent
gas from leaving the sinus during ascent. Sharp pain in the area of the affected
sinus results from the increased pressure. The pain is usually sufficient to stop the
diver from ascending. Pain is immediately relieved by descending a few feet.
From that point, the diver should slowly ascend until he gradually reaches the
surface.
While a diver is under pressure,
gas may form within his intestines or gas may be swallowed and trapped in the
stomach. On ascent, this trapped gas expands and occasionally causes enough
discomfort to require the diver to stop and expel the gas. Continuing ascent in spite
of marked discomfort may result in actual harm.
The inner ear contains no gas and is not subject to
barotrauma. However, the inner ear is located next to the middle ear cavity and is
affected by the same conditions that produce middle ear barotrauma. As the gas in
the middle ear is compressed or expands without the relief normally provided by
the eustachian tube, the fluid and membranes of the delicate inner ear will be functionally
disturbed. The membranes may tear as the pressure gradient increases.
The inner ear contains two important organs, the cochlea and the vestibular apparatus.
The cochlea is the hearing sense organ; damage to the cochlea can result in
symptoms of hearing loss and ringing in the ear (tinnitus).
The vestibular apparatus senses balance and motion; damage to the vestibular
apparatus may cause vertigo, which is the false sensation of a spinning type
of motion. The diver will feel that he or the surrounding area is spinning while in
fact there is no motion. One can usually tell this distinct sensation from the more
vague complaints of dizziness or lightheadedness caused by other conditions.
Vertigo is usually specific to the inner ear or that part of the brain that analyzes
inner ear input. Vertigo has associated symptoms that may or may not be noticed.
These include nausea, vomiting, loss of balance, incoordination, and a rapid
jerking movement of the eyes (nystagmus). Vertigo may also be caused by arterial
gas embolism or Type II decompression sickness, which are described in volume
5.
Frequent oscillations in middle ear pressure associated with difficult clearing may
lead to a condition of transient vertigo called alternobaric vertigo of descent. This
vertigo usually follows a Valsalva maneuver, often with the final clearing episode just as the diver reaches the bottom. The vertigo is short-lived but may cause
significant disorientation.
Alternobaric vertigo may also occur during ascent in association with middle ear
overpressurization. In this case, the vertigo is often preceded by pain in the ear that
is not venting excess pressure. The vertigo usually lasts for only a few minutes,
but may be incapacitating during that time. Relief is abrupt and may be accompanied
by a hissing sound in the affected ear. Alternobaric vertigo during ascent
disappears immediately when the diver halts his ascent and descends a few feet.
A pressure imbalance between the middle ear and external
environment may cause lasting damage to the inner ear if the imbalance is sudden
or large. This type of inner ear barotrauma is often associated with round or oval
window rupture.
There are three bones in the middle ear: the malleus, the incus, and the stapes.
They are commonly referred to as the hammer, anvil, and stirrup, respectively
(Figure 3-9). The malleus is connected to the eardrum (tympanic membrane) and
transmits sound vibrations to the incus, which in turn transmits these vibrations to
the stapes, which relays them to the inner ear. The stapes transmits these vibrations
to the inner ear fluid through a membrane-covered hole called the oval window.
Another membrane-covered hole called the round window connects the inner ear
with the middle ear and relieves pressure waves in the inner ear caused by movement
of the stapes.
Barotrauma can rupture the round window membrane, causing the inner ear fluid
(perilymphatic fluid) to leak. A persistent opening following barotrauma that
drains perilymphatic fluid from the inner ear into the middle ear is referred to as a
perilymph fistula. Perilymph fistula can occur when the diver exerts himself,
causing an increase in intracranial pressure. If great enough, this pressure can be
transmitted to the inner ear, causing severe damage to the round window
membrane. The oval window is very rarely affected by barotrauma because it is
protected by the foot of the stapes. Inner ear damage can also result from overpressurization
of the middle ear by a too-forceful Valsalva maneuver. The maneuver,
in addition to its desired effect of forcing gas up the eustachian tube, increases the
pressure of fluid within the inner ear. Symptoms of this inner ear dysfunction
include ringing or roaring in the affected ear, vertigo, disorientation, nystagmus,
unsteadiness, and marked hearing loss.
The diagnosis of inner ear barotrauma should be considered whenever any inner
ear symptoms occur during compression or after a shallow dive where decompression
sickness is unlikely. In some cases it is difficult to distinguish between
symptoms of inner ear barotrauma and decompression sickness or arterial gas
embolism. Recompression is not harmful if it turns out barotrauma was the cause
of the symptoms, provided the simple precautions outlined in volume 5 are
followed. When in doubt, recompress. All cases of suspected inner ear barotrauma
should be referred to an ear, nose and throat (ENT) physician as soon as possible.
Treatment of inner ear barotrauma ranges from bed rest to exploratory surgery,
depending on the severity of the symptoms.
figure3-9 Impedance Matching Components of Inner Ear.
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General Symptoms of Barotrauma
The predominant symptom of barotrauma is
pain. Other symptoms such as vertigo, numbness, or facial paralysis may be
produced depending on the specific anatomy. Pulmonary Overinflation Syndrome
is a potentially serious form of barotrauma and is discussed in detail later in this
chapter. In all diving situations, arterial gas embolism and decompression sickness
must be ruled out before the diagnosis of squeeze can be accepted.
Middle Ear Squeeze
Middle ear squeeze is the most common type of barotrauma.
The anatomy of the ear is illustrated in Figure 3-7. The eardrum completely seals
off the outer ear canal from the middle ear space. As a diver descends, water pressure
increases on the external surface of the drum. To counterbalance this pressure,
the air pressure must reach the inner surface of the eardrum. This is accomplished
by the passage of air through the narrow eustachian tube that leads from the nasal
passages to the middle ear space. When the eustachian tube is blocked by mucous,
the middle ear meets four of the requirements for barotrauma to occur (gas filled
space, rigid walls, enclosed space, penetrating blood vessels).
As the diver continues his descent, the fifth requirement (change in ambient pressure)
is attained. As the pressure increases, the eardrum bows inward and initially
equalizes the pressure by compressing the middle ear gas. There is a limit to this
stretching capability and soon the middle ear pressure becomes lower than the
external water pressure, creating a relative vacuum in the middle ear space. This
negative pressure causes the blood vessels of the eardrum and lining of the middle
ear to first expand, then leak and finally burst. If descent continues, either the
eardrum ruptures, allowing air or water to enter the middle ear and equalize the
pressure, or blood vessels rupture and cause sufficient bleeding into the middle ear
to equalize the pressure. The latter usually happens.
The hallmark of middle ear squeeze is sharp pain caused by stretching of the
eardrum. The pain produced before rupture of the eardrum often becomes intense
enough to prevent further descent. Simply stopping the descent and ascending a
few feet usually brings about immediate relief.
If descent continues in spite of the pain, the eardrum may rupture. Unless the diver
is in hard hat diving dress, the middle ear cavity may be exposed to water when
the ear drum ruptures. This exposes the diver to a possible middle ear infection
and, in any case, prevents the diver from diving until the damage is healed. At the
time of the rupture, the diver may experience the sudden onset of a brief but
violent episode of vertigo (a sensation of spinning). This can completely disorient
the diver and cause nausea and vomiting. This vertigo is caused by violent disturbance
of the malleus, incus, and stapes, or by cold water stimulating the balance
mechanism of the inner ear. The latter situation is referred to as caloric vertigo and
may occur from simply having cold or warm water enter one ear and not the other.
The eardrum does not have to rupture for caloric vertigo to occur. It can occur as
the result of having water enter one ear canal when swimming or diving in cold
water. Fortunately, these symptoms quickly pass when the water reaching the
middle ear is warmed by the body.
figure3-7 Gross Anatomy of the Ear in Frontal Section.
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Preventing Middle Ear Squeeze
Diving with a partially blocked eustachian tube
increases the likelihood of middle ear squeeze. Divers who cannot clear their ears
on the surface should not dive. Divers who have trouble clearing their ears shall be
examined by medical personnel before diving.
The possibility of barotrauma can be virtually eliminated if certain precautions are
taken. While descending, stay ahead of the pressure. To avoid collapse of the
eustachian tube and to clear the ears, frequent adjustments of middle ear pressure
must be made by adding gas through the eustachian tubes from the back of the
nose. If too large a pressure difference develops between the middle ear pressure
and the external pressure, the eustachian tube collapses as it becomes swollen and
blocked. For some divers, the eustachian tube is open all the time so no conscious
effort is necessary to clear their ears. For the majority, however, the eustachian
tube is normally closed and some action must be taken to clear the ears. Many
divers can clear by yawning, swallowing, or moving the jaw around.
Some divers must gently force gas up the eustachian tube by closing their mouth,
pinching their nose and exhaling. This is called a Valsalva maneuver. If too large a
relative vacuum exists in the middle ear, the eustachian tube collapses and no
amount of forceful clearing will open it. If a squeeze is noticed during descent, the
diver shall stop, ascend a few feet and gently perform a Valsalva maneuver. If
clearing cannot be accomplished as described above, abort the dive.
WARNING Never do a forceful Valsalva maneuver during descent or ascent. During
descent, this action can result in alternobaric vertigo or a round or oval
window rupture. During ascent, this action can result in a pulmonary
overinflation syndrome.
Treating Middle Ear Squeeze
Upon surfacing after a middle ear squeeze, the
diver may complain of pain, fullness in the ear, hearing loss or even mild vertigo.
Occasionally, blood may be in the nostrils as the result of blood being forced
through the eustachian tube by expanding air in the middle ear. The diver shall
report this to the diving supervisor and seek medical attention. Treatment consists
of taking decongestants and cessation of diving until the damage is healed.
Sinus Squeeze
Sinuses are located within hollow spaces of the skull bones and
are lined with a mucous membrane continuous with that of the nasal cavity (Figure
3-8). The sinuses are small air pockets connected to the nasal cavity by narrow
passages. If pressure is applied to the body and the passages to any of these sinuses
are blocked by mucous or tissue growths, pain will soon be experienced in the
affected area. The situation is very much like that described for the middle ear.
figure3-8 Location of the Sinuses in the Human Skull.
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Causes of Sinus Squeeze
When the air pressure in these sinuses is less than the
pressure applied to the tissues surrounding these incompressible spaces, the same
relative effect is produced as if a vacuum were created within the sinuses: the
lining membranes swell and, if severe enough, hemorrhage into the sinus spaces.
This process represents nature’s effort to balance the relative negative air pressure
by filling the space with swollen tissue, fluid, and blood. The sinus is actually
squeezed. The pain produced may be intense enough to halt the diver’s descent.
Unless damage has already occurred, a return to normal pressure will bring about
immediate relief. If such difficulty has been encountered during a dive, the diver
may often notice a small amount of bloody nasal discharge on reaching the
surface.
Divers should not dive if any signs of nasal congestion
or a head cold are evident. The effects of squeeze can be limited during a dive
by halting the descent and ascending a few feet to restore the pressure balance. If
the space cannot be equalized by swallowing or blowing against a pinched-off
nose, the dive must be aborted.
Tooth squeeze occurs when a small pocket of
gas, generated by decay, is lodged under a poorly fitted or cracked filling. If this
pocket of gas is completely isolated, the pulp of the tooth or the tissues in the tooth
socket can be sucked into the space causing pain. If additional gas enters the tooth
during descent and does not vent during ascent, it can cause the tooth to crack or
the filling to be dislodged. Prior to any dental work, personnel shall identify themselves
as divers to the dentist.
A diver who wears ear plugs, has an infected external ear
(external otitis), has a wax-impacted ear canal, or wears a tight-fitting wet suit
hood, can develop an external ear squeeze. The squeeze occurs when gas trapped
in the external ear canal remains at atmospheric pressure while the external water
pressure increases during descent. In this case, the eardrum bows outward (opposite
of middle ear squeeze) in an attempt to equalize the pressure difference and
may rupture. The skin of the canal swells and hemorrhages, causing considerable
pain.
Ear plugs must never be worn while diving. In addition to creating the squeeze,
they may be forced deep into the ear canal. When a hooded suit must be worn, air
(or water in some types) must be allowed to enter the hood to equalize pressure in
the ear canal.
When making a breathhold dive, it is possible to reach
a depth at which the air held in the lungs is compressed to a volume somewhat
smaller than the normal residual volume of the lungs. At this volume, the chest
wall becomes stiff and incompressible. If the diver descends further, the additional
pressure is unable to compress the chest walls, force additional blood into the
blood vessels in the chest, or elevate the diaphragm further. The pressure in the
lung becomes negative with respect to the external water pressure. Injury takes the
form of squeeze. Blood and tissue fluids are forced into the lung alveoli and air
passages where the air is under less pressure than the blood in the surrounding
vessels. This amounts to an attempt to relieve the negative pressure within the
lungs by partially filling the air space with swollen tissue, fluid, and blood.
Considerable lung damage results and, if severe enough, may prove fatal. If the
diver descends still further, death will occur as a result of the collapse of the chest.
Breathhold diving shall be limited to controlled, training situations or special operational
situations involving well-trained personnel at shallow depths.
P
A surface-supplied diver who suffers a loss of gas pressure or hose rupture with
failure of the nonreturn valve may suffer a lung squeeze, if his depth is great
enough, as the surrounding water pressure compresses his chest.
Scuba face masks, goggles, and certain types of exposure
suits may cause squeeze under some conditions. The pressure in a face mask can
usually be equalized by exhaling through the nose, but this is not possible with
goggles. Goggles shall only be used for surface swimming. The eye and the eye
socket tissues are the most seriously affected tissues in an instance of face mask or
goggle squeeze. When using exposure suits, air may be trapped in a fold in the
garment and may lead to some discomfort and possibly a minor case of hemorrhage
into the skin from pinching.
Expanding gas in the
middle ear space during ascent ordinarily vents out through the eustachian tube. If
the tube becomes blocked, pressure in the middle ear relative to the external water
pressure increases. To relieve this pressure, the eardrum bows outward causing
pain. If the overpressure is significant, the eardrum may rupture and the diver may
experience the same symptoms that occur with an eardrum rupture during descent
(squeeze).
The increased pressure in the middle ear may also affect nearby structures and
produce symptoms of vertigo and inner ear damage. It is extremely important to
rule out arterial gas embolism or decompression sickness when these unusual
symptoms of reverse middle ear squeeze occur during ascent or upon surfacing.
A diver who has a cold or is unable to equalize the ears is more likely to develop
reverse middle ear squeeze. There is no uniformly effective way to clear the ears
on ascent. Do not perform a Valsalva maneuver on ascent, as this will increase the
pressure in the middle ear, which is the direct opposite of what is required. The
Valsalva maneuver can also lead to the possibility of an arterial gas embolism. If
pain in the ear develops on ascent, the diver should halt the ascent, descend a few
feet to relieve the symptoms and then continue his ascent at a slower rate. Several
such attempts may be necessary as the diver gradually works his way to the
surface.
