3. Effects of Pressure Changes.pdf

EFFECTS OF PRESSURE CHANGES The most prevalent consequences of exposure to pressure changes in aviation is the Baro traumas. Barotraumas are almost an aviation specific health disorder. As per research work publications: The prevalence of barotitis amongst 45 children and 49 adults in transit was...

EFFECTS OF PRESSURE CHANGES The most prevalent consequences of exposure to pressure changes in aviation is the Baro traumas. Barotraumas are almost an aviation specific health disorder. As per research work publications: The prevalence of barotitis amongst 45 children and 49 adults in transit was found to be highest in children, 28%, compared with adults, 10%. Only 6% of the children with negative middle ear pressure after flight managed a successful Valsalva maneuver, whereas 33% could normalize the middle ear pressure by inflating the Otovent. Human body contains the 3 states of matter , the solid, the liquid & the gas. The gas is existed in a closed & a semi - closed cavities In this lecture we will describe:  The gas containing cavities in human body.  The mechanisms which allow pressure equilibration during changing environmental pressure.  Problems which can arise when gas equilibration fail to occur. GAS CONTAINING CAVITIES SEMI CLOSED CAVITIES • Middle Ear • Para-nasal sinuses • Lungs CLOSED CAVITIES • GIT • Teeth (Induced) EUSTACHIAN TUBES: • Also called Auditory Tube • It is the ventilating tube of the M.C. that connects the M.E. with the Nasopharynx Function in aviation is Equalizing pressure. • Composed of 2 portions:  The distal 2 thirds (24mm) is the Pharyngeal Cartilaginous portion.  The proximal third (12mm) is the Tympanic Bony portion. • The smallest diameter of the tube is at the junction between the 2 portions (isthmus). • The epithelial lining of the tube is stratified columnar ciliated epithelium. • The cilia beats towards the nasopharynx (like bird’s feather) or (palm leaves). • The bony portion is patent while the cartilaginous portion (the tensor palati and the levator palate) contraction of these muscles results in an opening of the tube. On swallowing and yawning, these muscles contract and open the tube. FACTS: o Because of the cilia arrangement of the epithelium lining the tube, passage of air from the M.E. to the nasopharynx is easier than from nasopharynx to the M.E. For that, the E.T. is considered as one-way flutter valve. o In the resting phase, the tube is passively closed. o Active opening of the tube occurs on contraction of both tensor and levator palate muscles o Passive opening of the tube occurs by passage of air from the M.E. when the pressure changes reaches 15mmHg (click). • Boyls’ law can be applied to these gases. • Boyls’ law states that, “At constant temperature, the volume of a given mass of gas is inversely proportional to the pressure to which it is subjected; expressed as: P1 V2 = P2 V1 or 1 P∝ V • In AVIATION: During Ascend→↓Barometric pressure →Relatively higher gases pressure During Descend→↑Barometric pressure →Relatively lower gases pressure - In Ascend, gases pass from cavities to outside. - In Descend, gases pass from outside to cavities. BAROTRAUMA • Defined as inflammation of the mucous membrane lining the air containing cavities due to pressure changes. Types • Otitic Barotrauma Barotitin Media • Sinus Barotrauma Barotitin Externa • Barodontalgia Barotitin Interna • G.I.Barotrauma BARODONTALGIA (Dental or Tooth Barotrauma) • Pain in a tooth caused by a change in ambient pressure. It may be severe enough to lead to inflight incapacitation of the pilot. MECHANISM: Occurs when? • A gas bubble is trapped in the tooth body after an improper tooth filling (defective tooth restoration) • A gas bubble is trapped in the tooth body due to dental caries, pulpitis, pulp necrosis, periodontal pockets, etc. • Expansion on the gas bubble will apply a pressure on the nerve ending of the tooth and cause pain proportional with the pressure change. TREATMENT: Restoration of pressure is the urgent need then repeating the endodontic treatment or extracting the tooth. Barotitis Media Can be defined as: An acute or chronic traumatic inflammation in the M.E. space that is produced by a pressure differential between the air in the tympanic cavity+mastoid air cells and that of the surrounding atmosphere. *The M.E. space is a rigid-walled cavity communicates with nasopharynx by the E.T. which acts as a one-way flutter valve that favors the release of pressure from the M.E. to the nasopharynx but not the reserve. • Ascent produces a relatively positive pressure in the tympanic cavity as the pressure of the atmosphere become progressively less. This positive P usually is readily equalized because the air can pass easily through the E.T. to the N.P. • The pressure change is greater at lower altitudes because the air is denser. * The relative positive pressure in the M.E. may be perceived by the individual as a slight fullness in the air, which usually can be relieved readily by swallowing. * On descent, a different situation exists. The E.T. remains closed unless actively opened by muscle action or high positive pressure in the N.P. When the ET opens, any existing pressure differential is immediately equalized. * If the E.T. were not open regularly during descent, a pressure differential may develop. If this pressure differential reach 80-90mmHg, the small muscles of the soft palate will not be able overcome it. Then either: re-ascent or an unphysiologic maneuver would be necessary to open the tube. At Sea Level Barotitis media or earblock results from failure of ventilation of the M.E. space on changing from low to high atmospheric pressure (descent). * The most common cause is swelling of the nasopharyngeal end of the E.T., which is usually due to active URTI or edema secondary to allergic rhinitis. * Ignorance of the necessity for swallowing at frequent intervals during descent may be a contributory factor. Preflight indoctrination is valuable. * The rate of descent is also significant factor. The descent rate of commercial flight is quite gradual = <400meter/min The descent rate of military A/C is much greater = >2000 meter/min * Delayed Otitic Barotrauma The use of O2 during flight will increase incidence of O.B., because the O2 used in A/C is usually dry and may irritate the mucosa of the upper respiratory tract. + The O2 will be absorbed by the M.E. mucosa → relative negative pressure (vaccum)→(Delayed Barotin Media) specially if the pilot go to sleep after the flight (sleep usually combined with infrequency of swallowing). Pathology of Barotitis Media Pathologic changes varies with the magnitude of the pressure differential, and with the length of time the pressure alteration acts on the tissues before equalization takes place. • Mild Pressure Differential → Partial Vaccum in the ME → Retraction of TM + engorgement of the blood vessels in the eardrum and ME mucosa * If pressure differential is great enough and persists long enough, a Transudate usually forms, which may be serious, or even hemorrhagic. Severe = Eardrum may rupture. The perforation usually occurs in the weakest area or area previously damaged by another pathologic process. After transudation, fluid accumulates in the ME space → the Tension on the ET will relieve → reinflation of the ME space, manifested by bubbling. Symptoms of Barotitis Media Also vary with the magnitude of the P.D. and with speed which it develops. Mild Barotrauma → Discomfort to mild ear pain + Feeling of fullness in the ear + mild conductive hearing loss - Low pitched tinnitus may be felt * In this category, symptoms usually disappears quickly and completely soon after the M.E. is ventilated. Moderate With transudate → will feel the fluid movement as the head position is change. Severe → The pain will be so great that it is incapacitating - The hearing loss will be greater - Louder tinnitus * Sometimes, the labyrinth stimulated by the pressure changes that is applied to the oral and round windows → vertigo (uncommon) but significant because it is disabling. * If TM ruptured, pain and other symptoms usually subsides quickly. Clinical Findings of Barotitis Media (Signs) * Vary with the degree of pressure changes and the length of time the condition has been present. * Retraction of TM with prominence of the short process of the malleus (what is referred to as “foreshortening” of its long process). * Vascular engorgement produces hyperemia of the eardrum * Hemorrhagic areas may be seen in the eardrum most likely along the long process of the malleus. * The formation of transudate may be manifested an air-fluid interface in the form of straight line that shifts with the changes in head position. Or by bubbles * A hemorrhagic transudate produces a Hemotympanum * Perforation may be seen Therapeutic Measures 1. Inflight Measures (Employed by Aircrew) - Performance of valsalva maneuver as soon as feeling fullness is noted in either ear. - When nasal decongestant is available, the nose should be sprayed Procedure of spraying: spray both nasal cavities initially – Then apply a second spray a few minutes after the initial application took effect – The second application will have a better chance to reach the N.P. and shrinking the mucosa around tubal orifices) If these procedures fail a rectum to higher altitude should by done when operational conditions permit. Then this will be followed by gradual descent while the individual performs the valsalva maneuver frequently. 2. Post-flight Measures (Employed by the Doctor) When aircrew present to the clinician with ear block Management will be based on clinical findings. * If no evidence of Transudation → attempt should be made to ventilate the ear. By Politzerization (Poltzer Bag) * If Transudation in ME has occurred, no attempt should be made to ventilate the ear. The formation of the fluid usually eliminates any persisting P.D. and relieve any pain. The main complaint is the feeling of fullness in the ear + mild hearing loss. Conservative treatment consist of topical and systemic decongestant. * Therapy must be continued until the ET & ME fiunctions normally. * It is imperative that the aircrew be grounded for this period and that they not be returned to flying duties prematurely. * Hematympanum, also, should be managed conservatively. Up to several weeks, may be required for blood to clear from the M.E. space. * Myringotomy * Myringotomy should be avoided if possible. * The only absolute indication for myringotomy would be the need for the aircrew member to return to flying duties for some compelling operational reason * Myringotomy does not restore the E.T. to functional status, but it will open the M.E. space and prevent further trauma to the M.E. and relieve the ear symptoms. * Perforation of the TM should be treated conservatively. The ear should be kept dry. If heavily were not occur by the end of 2 weeks, referral to otologist to consider closure of perforation. * Catherization of the ET orifice is never indicated. It will further traumatize the tube. * Recurrent barotitis media indicated the problem of chronic ET obstruction which is usually secondary to a pathologic process like hypertrophic lymphoid tissue in the nasopharynx, allergic rhinitis, and chronic sinusitis. Treatment may be directed at the primary problem and may be either medical or surgical. Valsalva Maneuver It is one way to ventilate the M.E. cavities unphysiologically. “The individual inhales, close the nose with thumb and index fingers, then exhales with the mouth closed.” → Positive pressure quickly builds up in the nasopharynx. The exhalation effort is augmented until the pressure in the nasopharynx becomes great enough to open the E.T. and ventilate the M.E. space Other Maneuver for ventilating the Middle Ear Toynbee maneuver Toynbee maneuver, performed by swallowing when the nose is obstructed, leads in most cases to pressure changes in one or both middle ears, resulting in ventilating the middle ear cavity Preventive Measures * To prevent barotitis during descent in aviation, the ears have to be cleared several times by performing the Valsalva's manoeuvre. The manoeuvre is difficult for children to perform, and they are therefore at high risk of developing barotitis. An alternative treatment is autoinflation using the Otovent. This prophylaxis/treatment can be performed by the child with assistance from its parents as soon as or preferably before the descent has started. * In conclusion it is recommended to do autoinflation using the Otovent set by children and adults who have problems clearing their ears during flight. . Pulmonary (lung) barotrauma As pressure decreases, air expands—its volume increases. So, when divers fill their lungs with compressed air at 33 feet and ascend without freely exhaling, the volume of air doubles, causing the lungs to overinflate BAROSINUSITIS Definition Acute or chronic inflammation of one or more of the PNS produced by the development of a pressure differences, usually negative, between the air in the sinus cavity & the ambient atmosphere. It is much less common than Barotitis media. PNS - Are air containing cavities - 4 pairs, the biggest & most significant are the frontal sinuses because the nasofrontal duct is longer & tortuous. - Communicate with the nasal cavity - The larger sinuses are more often involved in Barotrauma. *During ascent: Air moves out through ostium until equilibrium is attained at altitude. *During Descent: Air moves back into the sinus cavity until equilibrium is again reached at the earth’s surface. These movements of air do not produce any symptoms. The free movement of air through its ostia may be impeded or blocked by pus or mucopurulent material or by redundant tissue or an anatomic deformity. If ostium is not well ventilating, the relatively positive pressure that develops during ascent pressure effect or no symptoms. On descent, negative pressure will develop within the sinus cavity → suck the material into the sinus ostium. In frontal sinuses with it rather long & tortuous naso frontal duct, the thick mucopurulent material can obstruct the duct & create a sinus block → purulent sinusitis. Pathology The production of relative negativity in the sinus cavity will result in space-filling phenomena (swelling of the MM + transudation of fluid into the nasal cavity). *Mild-moderate sinus barotrauma → vascular engorgement & generalized submucosal edema occur. *More severe barotrauma → mucosal detachment & submucosal hematoma may develop.. Symptoms Usually proportional to the severity of the trauma & vary from mild feeling of fullness in the involved sinus → excruciating pain. Pain can develop suddenly & be Incapacitating. Signs - Tenderness over the affected sinus - ST bloody discharge from the nose X-ray - Mucosal thickening (opaque sinus) - Air fluid level may be demonstrated Treatment - In mild cases, the involvement is usually self-limited. The resolution takes place within few hours. - In severe cases, the clinical course may run few days – few weeks. - In-flight treatment • Return to the altitude at which the pain started. (If op. condition permits). • Spraying the nose with nasal decongestant then descend slowly. - Post-flight treatment - An altitude chamber may be available, the patient returned to altitude then recompressed gradually. - Relieve pain, promote drainage from the sinus cavity & offer protection from infection (pain killer, decongestant (topical & systemic) & antibiotics). - For maxillary sinus, cannulating the sinus cavity maybe helpful. - Most cases of Barosinusitis can be managed conservatively & uneventful recovery will be achieved. - It is imperative that the patient remain grounded until fully recovered & the nose and PNS are functioning normally. - Pre-flight altitude chamber test is required to ensure the achievement of the full recovery. Prevention - Aircrew should not fly when they have upper RTI’s. - Any intra-nasal condition that could affect ventilation of the PNS should be corrected like significant septal deviation, or Nasal polyposis). - Cabin pressurization, reduced the incidence of such problems & if it will happen, it will be of lesser magnitude. Thank you