Image taken from US Department of OSHA website
The Middle Ear refers to a collection of bones (ossicles) and muscles contained within a chamber (tympanic cavity) that sit between the Outer Ear and the Inner Ear, bounded by the tympanic membrane (eardrum) and the oval window respectively. The eardrum transforms air pressure waves into physical vibrations – the middle ear amplifies these vibrations – the oval window allows the amplified vibrations to “flow” into the fluid-filled cochlea. Therefore, the primary function of the middle ear is to act as a mechanical amplifier. Without the middle ear 99.9% of the sound energy entering the outer ear, and vibrating the eardrum, would be reflected by the fluid-filled inner ear. This is because fluid has a much higher impedance to sound waves than air, which in contrast is a very efficient medium.
The middle ear
The eardrum is attached at the umbo to the ossicular chain, which consists of three tiny bones:
- malleus (hammer) which adjoins the eardrum
- incus (anvil) which links the two other bones
- stapes (stirrup) which is attached to the oval window.
It is these tiny bones that create the mechanical amplification. This amplification is variable, depending on the frequencies; higher frequencies need less amplification for transmission to the cochlea.
Normal Operation of the Middle Ear
Efficient hearing requires an intact tympanic membrane (eardrum), a normal ossicular chain, and a well-ventilated tympanic cavity. The tympanic cavity is air-filled and carved out of the temporal bone. For the eardrum to have maximal mobility, the air pressure on either side must be equal. This means the air pressure within the middle ear must equal that of the external environment. This is achieved via the Eustachian tube which connects the tympanic cavity to the throat/nasopharynx and acts as a pressure release valve to equalise the middle ear pressure to that outside.
Normally the walls of the Eustachian tube are collapsed, and jaw-moving actions such as swallowing, talking, yawning and chewing open the tube to allow air in or out as needed for equalisation.
Paranasal Sinuses (photograph by Hellerhof)
Sinuses are cavities within a bone or other tissue, and humans have many around their bodies.
For flight, we are concerned mostly with the “paranasal sinuses”, which are a group of four paired air-filled spaces that surround the nasal cavity and they are named after the facial bones in which they are located:
- the maxillary sinuses, the largest of the paranasal sinuses, are under the eyes, in the maxillary (cheek) bones
- the frontal sinuses, superior to the eyes, in the frontal bone, which forms the hard part of the forehead
- the ethmoid sinuses, which are formed from several discrete air cells within the ethmoid bone between the nose and the eyes
- the sphenoid sinuses, in the sphenoid bone at the centre of the skull base under the pituitary gland.
The paranasal sinuses are lined with respiratory epithelium; which is a moist tissue whose purpose is protection from potential damage caused by mucous movement, and also to act as a barrier to pathogens and particles.
The paranasal sinuses are joined to the nasal cavity via small orifices called ostia; these are normally clear and allow pressure to equalise between the sinus cavities and the external environment.
There are several competing hypotheses regarding the biological function and purpose of the paranasal sinuses, but it is possible that they serve no biological function at all.
Pressure Changes in Flight
Whether flying in an unpressurised or pressurised aircraft, passengers and crew will experience a decrease in ambient (environmental) pressure whilst climbing, and an increase in pressure during descents. Some of these changes can be quite rapid. Such changes in pressure, and the speed of change, are not normally experienced “on the ground”; a rare example concerns travelling on a train as it enters or exits a tunnel at great speed. Divers will also experience similar pressure changes as they descend and ascend.
In most people, the ability of the middle ear to equalise pressure via the Eustachian tubes is adequate to prevent discomfort and retain good hearing during all stages and profiles of flight. This is mostly achieved automatically, and any “lag” between the middle ear cavity and the aircraft cabin can usually be eliminated by gentle yawning or chewing. Sometimes, if pressure is felt within the ear, it is possible to force the issue by clasping the nose and blowing into a closed mouth (Valsalva method); what may be known as “popping” the ears. Even when the Eustachian tubes are infected (see below) it can be relatively easy to equalise the ears when adjusting to lower cabin pressure (i.e. when climbing). However, in the descent, even the Valsalva method may not “pop” the ears and the increased external pressure will cause great discomfort
Similarly, the ostia usually remain clear enough to allow equalisation between the paranasal sinus cavities and the external air pressure. There is no natural mechanism we can employ to hasten the equalisation of the sinuses as there is for the middle ear.
If the Eustachian tube(s) and/or the ostia become blocked, or partially blocked, then a pressure differential will exist across the eardrum(s) and parts of the face and skull respectively; this can lead to pain, which can become severe.
In the case of the eardrum, the tympanic membrane will be distorted inward or outward, depending on the direction of the pressure differential. The ensuing pain is known as otic barotrauma, and will be felt acutely in the ears, also affecting one’s hearing. Sinus barotrauma will be felt above the eyes, behind the nose and in the cheeks, and possibly with a sensation that the teeth and gums are affected.
Causes of Blockage to the Middle Ear & Sinuses
Apart from physiological reasons, the anatomic causes of blocked Eustachian tubes and ostia are practically identical and often the two events will occur together.
Most commonly, these causes are both bacterial and viral infections such as colds and flu; however, blockages can also occur as a reaction to allergies and various diseases. Because, in both the middle ear and the sinuses, a blockage means that mucous cannot be removed, it is possible for bacteria to grow in this mucous, causing further infection, such as sinusitis, and therefore prolonging the problem.
- Pain - Even moderate amounts of pain will distract an aircrew member from being able to conduct their tasks – they can become, effectively, incapacitated. In severe cases of barotrauma an aircrew member can be grounded for a long period, and may suffer a burst eardrum.
- Vertigo - If one ear equalises, but the other doesn’t, then a form of pressure vertigo can be experienced as dizziness, which is not helpful for aircrew, especially pilots.
- Disorientation - Blocked Eustachian tubes may also give rise to infection in the inner ear and therefore lead to risk of dizziness and spatial disorientation – both very serious flight hazards. The inner ear contains semi-circular canals which automatically detect accelerations in three dimensions and give us our “sense” of balance – where is up, down, left and right, and which way are we moving.
- Headache - Sinusitis may develop giving rise to a constant throbbing headache felt in the face (often under the eyes or in the upper teeth). The pain gets worse when you move your head, strain or bend down, and when you experience extreme changes in temperature. Your face will also feel tender to the touch, and you may have other general symptoms such as a runny nose and sore throat. The symptoms of a sinus headache can easily be confused with both migraine and tension headaches.
- Hearing - Unequalised ears result in distortions of the eardrum and therefore, hearing will be impaired, in terms of attenuation and also clarity. This can lead to pilots and cabin crew not hearing, or mishearing, critical instructions.
- Workload - Finally, but by no means least, it can be quite traumatic (and a distraction) having a colleague or passenger on-board suffering from blocked Eustachian tubes while descending. Pilots will need to balance the desire to get the patient to a medical facility as soon as possible against the need for a slow descent. A delayed and/or slowed descent will alter the flight profile, and will affect fuel burn, landing weights, power settings, perhaps arrival and approach path, and even management of the pressurisation system. All of these are additional to the pilots’ normal workload and concerns, and can potentially introduce hazards.
Treatment & Mitigating Measures
If symptoms of otic or sinus barotrauma, or discomfort, occur in-flight then action is required, depending on the stage of the flight profile (climb, cruise, or descent), the severity of the trauma, and also depending on whether the patient is a crew member or passenger. Solutions may include: an immediate return to the departure aerodrome; a reduced cruising altitude; pressurisation management; and, continuation to destination with the application of first aid. Most critical for severe cases will be the need to control the descent in stages, allowing the patient time to equalise their ears frequently. The most crucial stage (i.e. with the greatest pressure change) is the last few thousand feet of altitude.
An badly affected crewmember should be removed from duties. There can be some leeway if one of only two pilots is affected, depending on the severity of pain; but discussions will need to cover the potential symptoms of degraded hearing, performance and possible dizziness and imbalance.
All cabin and flight crew are regularly trained in first aid and the use of the first aid equipment on-board. This will include the use of nasal decongestants to assist in freeing up the Eustachian tubes and ostia, usually in connection with the Valsalva method of ear “popping”. They will also be familiar with the use of analgesics to relieve some of the associated pain.
The simplest measure to take is to never fly with a cold, flu, or any other similar illness and infection. Similarly, do not fly if you cannot equalise the pressure in your middle ears using the Valsalva method; perhaps making it a habit to check this before every flight is a good habit to adopt?
The common causes of blocked ostia and Eustachian tubes usually clear up within a period of a few weeks, and usually no long-term damage occurs. Symptoms, including sinusitis headaches, can be alleviated by an array of different prescribed and over the counter drugs and products. However, flight and cabin crew should not self-medicate and should consult their Company surgeon or private Doctor. For some persistent bacterial infections antibiotics may need to be prescribed, which may preclude any flying for the duration of the course (often 10-days).
Blockages resulting from allergic reactions may be relieved through decongestants and antihistamine, but ultimately the source of the allergy will need to be addressed.
"Kutoka kwa ""Mifupa ya Kati"" (Ossicles) na ""Misipu"" iliyo ndani ya chumba (Tympanic cavity) ambayo inakaa kati ya sikio la nje na sikio la ndani, iliyozungukwa na utando wa tympanic (eardrum) na dirisha la oval." Eardrum hubadilisha mawimbi ya shinikizo la hewa kuwa mtetemeko wa kimwili - sikio la kati huongeza sauti hizi - dirisha la mviringo huruhusu sauti zilizoongezwa "kuingia" ndani ya cochlea iliyojaa umajimaji. Kwa hiyo, kazi kuu ya sikio la kati ni kutenda kama kichocheo cha mitambo. Bila sikio la kati, 99.9% ya nishati ya sauti inayoingia sikio la nje na kusumbua utando wa sikio ingepigwa na sikio la ndani lililojaa umajimaji. Hii ni kwa sababu kioevu ina impedance kubwa zaidi kwa mawimbi ya sauti kuliko hewa, ambayo kwa kulinganisha ni kati ya ufanisi sana. Mfupa wa masikio (eardrum) ni sehemu ya chini ya kiungo cha masikio (umbo) na huunganishwa na mifupa mitatu: malleus (hammer), ambayo huunganisha na masikio (eardrum), incus (anvil), ambayo huunganisha na mifupa mingine miwili (stapes), na stent (stirrup). Ni mifupa hiyo midogo inayosababisha kuongezeka kwa sauti. Kuimarishwa hii ni kutofautiana, kulingana na masafa; masafa ya juu wanahitaji kuimarishwa kidogo kwa ajili ya maambukizi kwa cochlea. Uwezo wa kusikia kwa njia ya kawaida unahitaji utando wa tympanic (eardrum) usioharibiwa, mlolongo wa ossicular wa kawaida, na shimo la tympanic lenye hewa nzuri. Sehemu ya tympanic imejaa hewa na imekatwa kutoka kwenye mfupa wa kiwiko. Ili utando wa sikio uwe na mwendo wa juu zaidi, shinikizo la hewa upande mmoja lazima liwe sawa. Hilo lamaanisha kwamba shinikizo la hewa ndani ya sikio la kati lazima liwe sawa na lile la mazingira ya nje. Hii hutimizwa kupitia Eustachian tube ambayo inaunganisha tumbo la tympanic na koo na nasopharynx na hufanya kazi kama valve ya kutolewa kwa shinikizo ili kulinganisha shinikizo la sikio la kati na lile la nje. Kwa kawaida, kuta za Eustachian tubes huanguka, na hatua za kuhamisha taya kama vile kumeza, kuzungumza, kupiga mayowe na kutafuna kufungua tube ili kuruhusu hewa ndani au nje kama inahitajika kwa usawa. Sinus ya Paranasal (Pana-Nasal Sinus) ni sehemu ya ndani ya mfupa au tishu nyingine, na wanadamu wana mengi karibu na miili yao. Sinus ya juu (paranasal sinus) ni sehemu ya chini ya macho ambayo hufanyiza sehemu ngumu ya paji la uso, inayoitwa sinus etmoid, ambayo hufanyizwa na seli kadhaa za hewa ndani ya paji la uso kati ya pua na macho. Sinus ya paranasal imefunikwa na epithelium ya kupumua, ambayo ni tishu ya unyevu ambayo kusudi lake ni ulinzi dhidi ya uharibifu unaoweza kusababishwa na harakati za mucous, na pia kutenda kama kizuizi kwa vimelea na chembe. Sinus ya paranasal inaunganishwa na cavity ya pua kupitia mashimo madogo yanayoitwa ostia, ambayo kwa kawaida ni wazi na kuruhusu shinikizo la usawa kati ya cavities ya sinus na mazingira ya nje. Kuna nadharia kadhaa zinazopingana kuhusu kazi ya kibiolojia na kusudi la sinus za paranasal, lakini inawezekana kwamba hazitumiki kazi ya kibiolojia kabisa. Mabadiliko ya shinikizo katika ndege: Ikiwa unasafiri katika ndege isiyo na shinikizo au yenye shinikizo, abiria na wafanyakazi watapata kupungua kwa shinikizo la mazingira wakati wa kupanda, na kuongezeka kwa shinikizo wakati wa kushuka. Baadhi ya mabadiliko hayo yanaweza kutokea upesi sana. Mabadiliko kama hayo katika shinikizo, na kasi ya mabadiliko, si kawaida uzoefu <unk> juu ya ardhi <unk>; mfano nadra inahusu kusafiri juu ya treni kama inaingia au inatokea handaki kwa kasi kubwa. Wapiga-mbizi pia watapata mabadiliko kama hayo ya shinikizo wanapoteremka na kupanda. Katika watu wengi, uwezo wa sikio la kati kulinganisha shinikizo kupitia Eustachian tubes ni wa kutosha kuzuia usumbufu na kudumisha kusikia nzuri katika hatua zote na maelezo ya ndege. Hii ni zaidi ya mafanikio moja kwa moja, na yoyote <unk>lag<unk> kati ya kati ya sikio shimo na ndege cabin kawaida inaweza kuondolewa kwa upole yawning au kutafuna. Wakati mwingine, ikiwa shinikizo linahisiwa ndani ya sikio, inawezekana kulazimisha suala hilo kwa kufunga pua na kupuliza ndani ya mdomo uliofungwa (mbinu ya Valsalva); kile kinachoweza kujulikana kama <unk> popping <unk> masikio. Hata wakati Eustachian tubes ni kuambukizwa (tazama chini), inaweza kuwa rahisi kulinganisha masikio wakati wa kurekebisha kwa chini cabin shinikizo (yaani. wakati wa kupanda). Hata hivyo, katika kushuka, hata Valsalva mbinu inaweza si pop masikio na kuongezeka kwa shinikizo la nje kusababisha usumbufu mkubwa. kwa hiyo, ostia kawaida kubaki wazi kutosha kuruhusu equalization kati ya paranasal sinus cavities na shinikizo la hewa ya nje. Hakuna utaratibu wa asili tunaweza kutumia kuharakisha equalization ya sinuses kama kuna kwa ajili ya sikio la kati. Ikiwa Eustachian tube (s) au ostia (s) imefungwa, basi tofauti ya shinikizo itapatikana katika eardrum (s) na sehemu za uso na fuvu la kichwa. Katika kesi ya eardrum, utando tympanic itakuwa kupotoshwa ndani au nje, kulingana na mwelekeo wa tofauti ya shinikizo. Maumivu yanayotokea yanajulikana kama barotrauma ya otic, na yatahisiwa sana katika masikio, pia kuathiri kusikia kwa mtu. Sinus barotrauma inaweza kuonekana juu ya macho, nyuma ya pua na mashavu, na labda na hisia kwamba meno na nywele zimeathiriwa. Kwa sababu za anatomiki, kusimamishwa kwa Eustachian tubes na ostia ni sawa na mara nyingi matukio mawili yatatokea pamoja. Kwa kawaida, sababu hizi ni maambukizo ya bakteria na virusi kama vile homa na homa; hata hivyo, vizuizi vinaweza kutokea pia kama athari ya mzio na magonjwa mbalimbali. Kwa sababu, katika sikio la kati na sinusi, kuziba kunamaanisha kwamba utando hauwezi kuondolewa, inawezekana kwa bakteria kukua katika utando huu, na kusababisha maambukizi zaidi, kama vile sinusitis, na hivyo kupanua tatizo. - Maumivu - Hata kiasi cha wastani cha maumivu itamsumbua mwanachama wa wafanyakazi wa ndege kutoka kuwa na uwezo wa kufanya kazi zao <unk> wanaweza kuwa, kwa ufanisi, wasio na uwezo. Katika visa vikali vya barotrauma mwanachama wa wafanyakazi wa ndege anaweza kuwekwa ardhini kwa kipindi kirefu, na anaweza kuumia kwa kuvunjika kwa utando wa sikio. - Vertigo - Kama sikio moja equalizes, lakini nyingine haina, basi aina ya shinikizo vertigo inaweza kupatikana kama kizunguzungu, ambayo si muhimu kwa wafanyakazi wa ndege, hasa marubani. - Disorientation - Eustachian tubes blocked pia inaweza kusababisha maambukizo katika sikio la ndani na hivyo kusababisha hatari ya kizunguzungu na spatial disorientation <unk> wote hatari kubwa sana ndege. Masikio ya ndani yana mifereji ya nusu mviringo ambayo hutambua kasi katika vipimo vitatu na kutupa hisia yetu ya usawa, ambapo ni juu, chini, kushoto na kulia, na ni njia gani tunazunguka. - Ugonjwa wa kichwa - Sinusitis inaweza kutokea na kusababisha maumivu ya kichwa ya mara kwa mara ya kupigapiga katika uso (mara nyingi chini ya macho au katika meno ya juu). Maumivu huongezeka wakati unapoinua kichwa chako, unapojipinda au kukunjika, na wakati unapopata mabadiliko makubwa ya joto. Uso wako pia utahisi nyeti kwa kugusa, na unaweza kuwa na dalili nyingine za jumla kama vile pua inayotiririka na koo linaloumiza. Dalili za maumivu ya kichwa ya sinus zaweza kuchanganyikiwa kwa urahisi na maumivu ya kichwa ya kipandauso na maumivu ya kichwa ya mkazo. - Usikilizaji - Masikio yasiyo sawa husababisha upotoshaji wa eardrum na kwa hivyo, kusikia kutakuwa na kasoro, kwa suala la kupunguzwa na pia uwazi. Hilo laweza kusababisha marubani na wafanyakazi wa ndege wasisikie, au wasisikie vibaya, maagizo muhimu. - mzigo wa kazi - Mwishowe, lakini kwa njia yoyote chini, inaweza kuwa kabisa traumatic (na kuingilia) kuwa na mwenzake au abiria juu ya bodi mateso ya zilizofungwa Eustachian tubes wakati wa kushuka. "Wanaangaji wanahitaji kusawazisha tamaa ya kumpeleka mgonjwa kwenye kituo cha matibabu haraka iwezekanavyo na haja ya kushuka polepole. """ Kuchukua muda mrefu au kupunguza kasi ya kushuka kunaweza kuathiri matumizi ya mafuta, uzito wa kutua, mipangilio ya nguvu, labda njia ya kuwasili na kukaribia, na hata usimamizi wa mfumo wa shinikizo. Yote haya ni ya ziada kwa kazi ya kawaida ya marubani na wasiwasi, na inaweza uwezekano wa kuanzisha hatari. Matibabu na hatua za kupunguza: Ikiwa dalili za barotrauma ya otic au sinus, au usumbufu, hutokea katika ndege, basi hatua inahitajika, kulingana na hatua ya maelezo ya ndege (kupanda, cruise, au kushuka), uzito wa majeraha, na pia kulingana na ikiwa mgonjwa ni mwanachama wa wafanyakazi au abiria. Suluhisho inaweza ni pamoja na: kurudi mara moja kwa ndege ya kuondoka; kupunguzwa cruising urefu; usimamizi wa pressurization; na, kuendelea kwa marudio na matumizi ya msaada wa kwanza. Katika kesi kali, ni muhimu kudhibiti kushuka kwa hatua, kuruhusu mgonjwa wakati wa kusawazisha masikio yao mara kwa mara. Hatua muhimu zaidi (yaani na mabadiliko makubwa ya shinikizo) ni chache ya mwisho elfu futi ya urefu. Mwanachama wa wafanyakazi aliyeathiriwa vibaya anapaswa kuondolewa katika kazi yake. Kunaweza kuwa na nafasi ya kuingilia ikiwa mmoja tu kati ya marubani wawili ameathiriwa, kulingana na ukali wa maumivu; lakini majadiliano yatahitaji kufunika dalili za uwezekano wa kusikia, utendaji, na uwezekano wa kizunguzungu na kutofautiana. Wafanyakazi wote wa chumba cha abiria na wa ndege hufundishwa mara kwa mara katika matibabu ya kwanza na matumizi ya vifaa vya matibabu ya kwanza kwenye ndege. Hii itajumuisha matumizi ya decongestants pua kusaidia katika kuondoa up Eustachian tubes na ostia, kwa kawaida katika uhusiano na Valsalva mbinu ya sikio <unk>popping<unk>. Pia watakuwa na ufahamu wa matumizi ya dawa za kupunguza maumivu ili kupunguza baadhi ya maumivu yanayohusiana nayo. Hatua rahisi zaidi ni kutosafiri kwa ndege ukiwa na homa, mafua, au ugonjwa mwingine wowote unaofanana na huo. Kwa mfano, ikiwa unaweza kuondoa shinikizo la sikio la kati kwa kutumia njia ya Valsalva, unaweza kuepuka kutumia ndege. Kwa kawaida, sababu za kawaida za kufungwa kwa mifereji ya mkojo na ya Eustachian hutoweka baada ya majuma machache, na kwa kawaida hakuna madhara ya muda mrefu. Ugonjwa wa sinusitis unaweza kupunguzwa na dawa mbalimbali za dawa. Hata hivyo, wafanyakazi wa ndege na wa chumba cha abiria hawapaswi kujipatia dawa na wanapaswa kushauriana na daktari wao wa kampuni au daktari binafsi. Kwa baadhi ya maambukizi ya bakteria ya kudumu, antibiotics inaweza kuhitajika kuagizwa, ambayo inaweza kuzuia ndege yoyote kwa muda wa kozi (mara nyingi siku 10). Vizuizi vinavyotokana na athari za mzio vinaweza kuondolewa kwa kutumia dawa za kupunguza msukosuko na antihistamine, lakini mwishowe chanzo cha mzio kitahitaji kushughulikiwa.