|
One of the most important organs to the diver. This article explains the anatomy and how it is effected in the underwater environment.
Introduction
The ear is the organ of hearing and balance. It is divided into three parts:
- The outer Ear - consists of the lobe or Pinna, the Auditory Canal and ends with the Tympanic Membrane (ear drum)
- The middle ear - contains Ossicles. Hammer Anvil Stirrup, in that order, connecting the Tympanic Membrane with the Oval Window.
- The inner ear - contains three Semi-Circular Canals for balance (Vestibular Canals) with the Oval Window, the Round Window, Cochlea and Eustachian tube which connects Inner Ear with Naso-Pharynx.
These are important to divers in that, the pressure outside the ear must be the same as that on the inside else pain will result. If the pressure difference becomes too great the tympanic membrane may stretch and possibly perforate. This in turn will cause cause pain, dizziness, nausea and some bleeding from the ear.
How it works
Sound vibration is felt by the Tympanic membrane (ear drum) then transmitted and amplified through the Ossicles to the Oval window of the cochlea.
The cochlea and 3 Semi Circular Canals are filled with Perilymph, a fluid that transmits vibrations through the Cochlea. This is detected by the nerves and converted to nerve signals and transmitted to the Brain.
The Round Window works in unison with the Oval window to allow movement of Perilymph inside the Cochlea, i.e. when the Oval Window moves in the Round Window moves out.
The Ossicles
The ossicles are three tiny bones that connect the ear drum to the cochlear. They consist of the Malleus, Incus and Stapes or more commonly known the hammer, anvil and stirrup.
Their purpose is to transfer and amplify sound across the middle ear.
Ear Equalisation
As you descend, pressure increases on the dead air spaces in your body, especially the ears and sinuses. It also increases in the dead air space in your mask. This is because the air is being compressed. To equalize the air space, you need to add more air to these areas.
The sign that you need to equalize your ears is unmistakable. There will be a feeling of building pressure, and if you don't equalize, pressure can very quickly turn to pain. The solution is a technique called the Valsalva maneuver or more commonly 'ear clearing'.
To equalize, pinch your nose shut and gently try to exhale through it. The air you're trying to exhale will be blocked by your pinched nose, so it will end up in the dead air space in your ears, which equalizes the pressure. Swallowing also helps. Some people find that wiggling the jaw while swallowing is effective in stubborn cases. Most divers continually equalize their ears as pressure changes during a dive. Sooner or later, it becomes second nature.
If you can't equalize, don't force it. Signal to your buddy that you have a problem with your ears (see signals), rise up a couple of feet, until the pressure lessens, wait a few moments, then try again. Most people can equalize if they take it slowly enough. If you're on a group dive, the group may continue to descend at the normal pace. (This contingency should be covered in the dive briefing.) You and your buddy can keep track of the group by swimming above them or following the reference line, if there is one. Then you can descend at your own pace. If you can't equalize your ears, you'll have to abort the dive.
To equalize the air space in your mask, simply blow out through your nose.
Safety Tips
- Don't wait until your ears hurt. Start equalizing the moment you begin your descent. This prevents the painful buildup of pressure and keeps little problems from turning into big ones.
- Do not force it! Several slow, gentle attempts are better than one forced attempt, which can damage your ears.
- Never go deeper if you continue to experience pain. Stop or rise a little. Wait until the pain stops, then try again.
When performing the Valsalva manoeuvre it is possible to rupture the round window if effort is prolonged and excessive. If on the descent a diver does not equalise ears in time, the Ossicles press the Oval window inwards with a corresponding outward movement in the round widow. If then excessive and prolonged pressure is applied with the Valsalva manoeuvre the blood pressure momentarily increases causing the perilymph pressure to increase, which can then rupture the round window.
If you cannot equalize you have to end the dive.
Variations to Valsalva
In addition to the Valsalva manoeuvre there are a number of variations:
- Frenzel manoeuvre is like the Valsalva manoeuvre in that the diver blows air against the pinched nose, but the frenzel manoeuvre does not use the diaphragm to blow the air, into the eustachian tube, it uses the throat muscles to compress the air in the pharynx instead. The frenzel manoeuvre minimises probability of round windows rupture, but requires more time to master.
- Toynbee manoeuvre involves holding the nose and swallowing simultaneously. This usually causes the eustachian tubes to open momentarily, allowing air to enter the middle ear. The tubes open only momentarily and it causes a negative pressure in the pharynx, so only smaller amounts of air are able to pass into the middle ear space, so is not as effective as Valsalva.
- Edmonds (first technique) for clearing the ears is to open the eustachian tubes by wriggling the jaw from side to side or thrusting the jaw forward.
- Edmonds (second technique) "sniff and blow" is where you suck the cheeks in with a sniff against the closed nostrils immediately followed by a valsalva.
- Lowry technique is to swallow and blow at the same time. This is a Toynbee and valsalva combination.
Reversed Ear
Reversed ear is caused by blocking the outer ear (Auditory Canal may bleed to equalise pressure or Eustachian Tube blocking after start of dive.
Swimmer's Ear
Swimmer's Ear is a fairly common problem, that usually does not require medical attention. It is characterised by inflammation and painful infection of the outer ear. Our ears produce a protective ear wax that help to keep moisture out of the ear. However, when we use cotton swabs and other methods of removing the wax, we are allowing moisture and bacteria to enter the outer ear canal. This bacteria can multiply causing an infection and inflaming the surrounding tissue. Fortunately, Swimmer's Ear can often be treated with over the counter ear drops, and/or white vinegar which will help to kill the bacteria. Prevention is even more simple. When diving, one should either dry the ears thoroughly, or place a few drop of vinegar or alcohol in the ears following a dive to help promote drying. If the symptoms are severe, or if you have recurring cases of Swimmer's Ear, medical advice is recommended.
Sound
On the surface you can generally locate the direction of a sound, this is because the brain works so fast it can detect when a noise hits one ear before the other and it can differentiate that a noise is louder in one ear than in the other.
The outer part of the ear (pinna) channels sounds towards the eardrum and when a sound hits both ears at the same time and is of equal volume in each ear, and the sound is at its loudest, the listener will be facing the sound.
Sound travels at about 750 miles per hour on the surface but things are very different underwater. When a diver is underwater, sound travels 4 times faster in water due to its higher density, and the brain cannot detect the difference of sound hitting one ear before the other, furthermore the outer ears (pinna's) do not function the same, the outcome is that divers cannot tell the direction of sounds underwater.
Divers may be able to tell if a sound is getting fainter as they swim away from it, but sounds underwater can be heard from miles away, so you would have to swim a fair distance for the sounds to become noticeable fainter.
|
|
