question: What happens when we pop our ears underwater to equalize?
comment: Your eardrum is sealed so water can't get in, but it has air on both sides of it. The air on the inside of your eardrum has to be able to change pressure, because the air changes pressure, as you walk up a hill or the weather changes. This is done via a tube that links the back of your nasal cavity to the inner ear, and the space on the inside of your eardrum. It's a tiny tube, so it can only cope with slow changes of pressure (which is all you'd normally encounter). If you go up in an aeroplane, or drive up a big hill, the ambient pressure changes faster than the tubes can cope, so you get a sudden 'pop' of air coming in to equalize the pressure behind your ear. You can force air up this tube yourself by holding your nose and closing your mouth and just increasing the pressure as if you were blowing out. When you're underwater, the same principle applies. As you go down, the water presses harder on your eardrums, to a painful extent, until you hold your nose and blow, and what this does is effectively 'pump up' the space behind your eardrum with more air pressure, to allow it to equal the water pressure outside and stop your ears hurting.
passages: BULLET::::- Ears and sinuses: There is a risk of stretched or burst eardrums, usually crushed inwards during descent but sometimes stretched outwards on ascent. The diver can use a variety of methods to let air into or out of the middle ears via the Eustachian tubes. Sometimes swallowing will open the Eustachian tubes and equalise the ears.
   This might have occurred due to barotrauma of descent, and/or the effects of nasal decongestants. It is due to unequal increase in middle ear pressures on ascent, is usually mild, and most often cleared by further ascent. When the pressures in both ears reach ambient levels, the stimulus for the dizziness stops. Although most often mild, the vertigo can persist until the diver reaches the surface continuing the unequal pressures, which can damage the inner ear or ear drum.
   This bypassing of the middle ear also affects the frequency sensitivity of the ear. Sound is also reflected in proportion to the change of density or elasticity (mismatch of acoustic impedance) when passing through an interface, so that enclosing the head in a rigid helmet may cause a significant attenuation of sound originating in the water. Internal sound attenuation material my further reduce noise levels.
   Bone conduction plays a major role in underwater hearing when the head is in contact with the water (not inside a helmet), but human hearing underwater, in cases where the diver’s ear is wet, is less sensitive than in air.
   BULLET::::- further compression of the air follows from moving the closed glottis upwards (this is easily noticed in the elevation of the "Adam's Apple").
  
  By performing this technique, the compressed air is forced into Eustachian tubes, and thus into the middle ear. In situations where the ambient pressure rises (typical causes are decreasing altitude in the case of an airplane or increasing depth in the case of a diver submerging), the maneuver results in the equalization of the pressure on both sides of the eardrum.
   The effects of changes in atmospheric pressure upon water levels observed in wells has been known for many years. The effect is a direct one, an increase in atmospheric pressure is an increase in load on the water in the aquifer, which increases the depth to water (lowers the water level elevation). Pascal first qualitatively observed these effects in the 17th century, and they were more rigorously described by the soil physicist Edgar Buckingham (working for the United States Department of Agriculture (USDA)) using air flow models in 1907.
  
  Section::::Head loss.
   BULLET::::- Voluntary opening of the eustachian tubes French: (BTV) is a method of equalising or clearing the ears described by doctor Georges Delonca and used in scuba diving and freediving. It aims to rebalance the pressure between the external ear and middle ear.The subject must either exercise a voluntary control of the tensor veli palatini muscles opening the eustachian tubes, or move the jaw to open the tubes when necessary. Another description of the method is to tense the muscles of the soft palate and the throat while pushing the jaw forward and down as if starting to yawn. This should pull the eustachian tubes open.This is less easy to execute than the Valsalva maneuver, but the BTV is the gentlest method to clear the ears. However, not all divers can perform this maneuver. It may be necessary to engage in ear training exercises to train the muscles to perform this maneuver.*: Some people are able to voluntarily hold their Eustachian tubes open continuously for a period of several seconds to minutes. The 'clicking your ears' can actually be heard if one puts one's ear to another person's ear for them to hear the clicking sound. Those that are borderline on learning this voluntary control first discover this via yawning or swallowing or other means; which after practice can be done deliberately without force even when there are no pressure issues involved. When the Eustachian Tubes are deliberately held open, one's voice sounds louder in one's head than when they are closed.
   Section::::Normalizing middle-ear pressures.
  
  When rapid ambient pressure increase occurs as in diving or aircraft descent, this pressure tends to hold the Eustachian tubes closed, preventing pressure equalization across the ear drum, with painful results. To avoid this painful situation, divers, caisson workers and aircrew attempt to open the Eustachian tubes by swallowing, which tends to open the tubes, allowing the ear to equalize itself.
   The middle ear is hollow. In a high-altitude environment or on diving into water, there will be a pressure difference between the middle ear and the outside environment. This pressure will pose a risk of bursting or otherwise damaging the tympanum if it is not relieved. If middle ear pressure remains low, the ear drum may become retracted into the middle ear . One of the functions of the Eustachian tubes that connect the middle ear to the nasopharynx is to help keep middle ear pressure the same as air pressure. The Eustachian tubes are normally pinched off at the nose end, to prevent being clogged with mucus, but they may be opened by lowering and protruding the jaw; this is why yawning or chewing helps relieve the pressure felt in the ears when on board an aircraft.
   Sound travels about 4.5 times faster in water than in air, and at a similarly higher speed in body tissues, and therefore the interval between a sound reaching the left and right inner ears is much smaller than in air, and the brain is less able to discriminate the interval which is how direction of a sound source is identified. Some sound localisation is possible, though difficult.
   To allow successful equalization when diving, it is important that the diving suit hood does not make an airtight seal over the outside ear hole, and that earplugs are not worn. It is not recommended to dive when a eustachian tube is congested or blocked, e.g. with the common cold, as this may cause what is known as a reverse block. Descent is uninhibited as the Valsalva maneuver may still clear the eustachian tubes temporarily by force, but during ascent a blockage may stop the air in the middle ear (which is now at depth pressure) from escaping as the diver ascends. The eardrum then bursts outwards, causing the same hazards as with an ordinary burst eardrum, such as cold water in the middle ear deranging the working of the sense organs of balance in the inner ear.
   Normally, the Eustachian tube is collapsed, but it gapes open both with swallowing and with positive pressure. When taking off in an airplane, the surrounding air pressure goes from higher (on the ground) to lower (in the sky). The air in the middle ear expands as the plane gains altitude, and pushes its way into the back of the nose and mouth. On the way down, the volume of air in the middle ear shrinks, and a slight vacuum is produced. "Active" opening of the Eustachian tube is required to equalize the pressure between the middle ear and the surrounding atmosphere as the plane descends. A diver also experiences this change in pressure, but with greater rates of pressure change; active opening of the Eustachian tube is required more frequently as the diver goes "deeper" into higher pressure.
   The pressure changes during ascent and descent may affect gas spaces in the diver and diving equipment. A change in pressure will cause a pressure difference between the gas space and environment which will cause the gas to expand or compress if that is possible, and constraining the gas from expanding or compressing to balance the pressure may cause damage to the surrounding material or tissues by over-expansion or crushing. Some gas spaces, such as the mask, will automatically release excess gas as it expands, but have to be equalized during compression, others, such as the buoyancy compensator bladder, will expand until the over-pressure valve opens. The ears are a special case, as they will usually vent naturally through the Eustachian tubes, but these may be blocked. During descent they do not usually equalize automatically, and must be intentionally equalized by the diver, using one of several possible methods. Most of the physiological airway automatically equalizes as long as the diver is breathing normally, but holding the breath can prevent equalization of the lower airways and lungs, which can lead to barotrauma.
   People who do intense weight lifting, like squats, may experience sudden conductive hearing loss due to air pressure building up inside the ear. They are advised to engage in an ear clearing method to relieve pressure, or pain if any.
  
  Section::::Methods.
  
  The ears can be cleared by various methods, some of which pose a distinct risk of barotrauma including perforation of the eardrum: 
  
  BULLET::::- Yawning which helps to open the eustachian tubes;
  
  BULLET::::- Swallowing which helps to open the eustachian tubes;
   No single method is considered safest or most successful in equalization of the middle ear pressure. Using alternative techniques may improve the success individually when a technique fails.
  
  Section::::Precautions.
  
  The pressure difference between the middle ear and the outside, if not released, can result in a burst eardrum. This damages hearing, and if this occurs underwater, cold water in the middle ear chills the inner ear, causing vertigo. The pressure difference can also cause damage to other body air spaces, such as the paranasal sinuses. This can also be caused by damaged sinus ducts.
   Flooding of a free-flow helmet may be managed by increasing flow rate and either opening the neck seal with the fingers or tilting the head to allow the water to flow out through the exhaust port.
  
  Section::::Basic skills.:Adjusting the breathing resistance.
   In demand valves where the cracking pressure is adjustable by the diver, it may also occur as a result of maladjustment of the cracking pressure (dial a breath) knob. In these cases the freeflow can usually be eliminated by adjusting the setting.
   Ear clearing
  
  Ear clearing or clearing the ears or equalization is any of various maneuvers to equalize the pressure in the middle ear with the outside pressure, by letting air enter along the Eustachian tubes, as this does not always happen automatically when the pressure in the middle ear is lower than the outside pressure. This need can arise in scuba diving, freediving/spearfishing, skydiving, fast descent in an aircraft, fast descent in a mine cage, and being put into pressure in a caisson or similar pressure-bearing structure, or sometimes even simply travelling at fast speeds in an automobile.
   Equalizing of the ears and mask are part of the essential skills for any form of diving, and equalizing of the airways is necessary for any form of diving where the diver breathes under pressure. This is provided for by breathing normally, and is the reason why divers are advised not to hold their breath while changing depth.
  
  Section::::Underwater communications.
  
  Divers need to communicate underwater to co-ordinate their dive, to warn of hazards, to indicate items of interest and to signal distress.
   BULLET::::- Helmet flood. Depending on the severity of the flood, this can range from an annoyance to an emergency. A slow leak can be controlled by opening the free flow valve, which will drive a moderate flow of water out of the exhaust valve. A neck dam failure usually has this effect.
   The permit for the Macondo Prospect by the Minerals Management Service in 2009 did not require redundant acoustic control means. Insofar as the BOPs could not be closed successfully by underwater manipulation (ROV Intervention), pending results of a complete investigation, it is uncertain whether this omission was a factor in the blowout.
   Barotrauma of ascent is caused by pressure differences between the decreasing ambient pressure and the internal pressure of gas filled spaces of the diver's body. The two organs most susceptible to barotraumas of ascent are the ears and lungs, and both will normally equalize automatically. Problems may arise in the middle ear if the Eustachian tubes become blocked during the dive, and the lungs can be injured if the diver forcibly holds his or her breath during ascent, which can occur during an emergency free ascent. As lung overexpansion injury is potentially life-threatening, entry level diver training emphasizes developing the habits of not holding one's breath while diving on scuba, and slow continuous exhalation during simulated emergency swimming ascents. Techniques for clearing blocked Eustachian tubes during ascent are also generally taught at entry level.
   If this fails, then the Valsalva maneuver may be used. This maneuver, when used as a tool to equalize middle ear pressure, carries with it the risk of auditory damage from over pressurization of the middle ear. It is safer, if time permits, to attempt to open the Eustachian tubes by swallowing a few times, or yawning, or by using the Valsalva technique of breathing a very small amount of air gently into nostrils held closed by the fingers as soon as mild pressure is felt, before it increases to the point that its release would be painful. The effectiveness of the "yawning" method can be improved with practice; some people are able to achieve release or opening by moving their jaw forward or forward and down, rather than straight down as in a classical yawn, and some can do so without moving their jaw at all by activating the tensor tympani muscle, which is heard by the individual as a deep, rumbling sound. Opening can often be clearly heard by the practitioner, thus providing feedback that the maneuver was successful.
   Hearing threshold and the ability to localize sound sources are reduced underwater in humans, but not in aquatic animals, including whales, seals, and fish which have ears adapted to process water-borne sound.
  
  Section::::In vertebrates.
   Alternobaric vertigo is most pronounced when the diver is in the vertical position; the spinning is towards the ear with the higher pressure and tends to develop when the pressures differ by 60 cm of water or more. Ear clearing may be a remedy. A similar vertigo can also occur as a result of unequal heating stimulation of one inner ear labyrinth over the other due to diving in a prone position in cold water - the undermost ear being stimulated.
  
  Section::::Diagnosis.
  