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.

3-8.1 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.

3-8.2 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.

3-8.3 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

Picture Section Human Ear
Figure 3-7. Gross Anatomy of the Ear in Frontal Section.

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.

3-8.3.1 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.

3-8.3.2 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.

3-8.4 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.

3-8.4.1 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.

Location Sinuses
Figure 3-8. Location of the Sinuses in the Human Skull.

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.

3-8.4.2 Preventing Sinus Squeeze. 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.

3-8.5 Tooth Squeeze (Barodontalgia). 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.

3-8.6 External Ear Squeeze. 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.

3-8.7 Thoracic (Lung) Squeeze. 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.

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.

3-8.8 Face or Body Squeeze. 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.

3-8.9 Middle Ear Overpressure (Reverse Middle Ear Squeeze). 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.

3-8.10 Sinus Overpressure (Reverse Sinus Squeeze). 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.

3-8.11 Overexpansion of the Stomach and Intestine. 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.

3-8.12 Inner Ear Dysfunction. 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).

3-8.12.1 Vertigo. 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.

3-8.12.2 Inner Ear Barotrauma. 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.

Figure 3-9. Impedance Matching Components of Inner Ear.

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 overpres-surization 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.

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