2024.06.26 - Aerospace Physiology (Cataman).pdf

 Aviation Physiology: Hyperventilation signs and symptoms Barotrauma Decompression sickness Basic Course in Aviation Medicine Dr. Elena Cataman 25/06/2024 The ESAM...

 Aviation Physiology: Hyperventilation signs and symptoms Barotrauma Decompression sickness Basic Course in Aviation Medicine Dr. Elena Cataman 25/06/2024 The ESAM ACADEMY 2 Lecture overview Hyperventilation signs and symptoms Barotrauma Decompression sickness 25/06/2024 The ESAM ACADEMY 3  Hyperventilation (definition) An excessive rate and depth of respiration leading to the abnormal loss of CO2 from the blood. Hyperventilation is a condition where the rate and depth of breathing is abnormally increased This causes an excessive loss of carbon dioxide from the body causing a chemical imbalance in the blood  Hyperventilation (introduction) Introduction Carbon dioxide has a very important role ― in maintaining chemical balance in the body and ― controlling breathing Excess Carbon dioxide is eliminated by the lungs during exhalation. Some carbon dioxide must remain in the body for the proper pH balance of the blood The concentration of this gas in the body is monitored closely by the brain Increased rate and depth of breathing leads to a sharp gas imbalance - carbon dioxide is actively exhaled, while inhaling its reserves are not replenished.  Hyperventilation Introduction (Control of breath) The average adult breathing cycle is 12 – 16 breaths per minute ― Directly correlates to amount of carbon dioxide in blood Breathing rate can be stimulated or slowed down through voluntary When exposed to situations of emotional stress, fear, anxiety, apprehension or pain the human body usually reacts by breathing faster than normal. This reaction is a hyperventilation muscle  Hyperventilation (Causes) Introduction emotional stress (fear, worries, anxiety, anger), stress, state of panic, obsessive fears, severe nervous overexcitation, pain attack, overdose of medication, e.g. aspirin  Hyperventilation (Effects) Introduction The brain defends itself against this involuntary imbalance by restricting it’s blood flow This restriction of blood flow to the brain will cause individuals to experience symptoms that could jeopardize safety Significance of this syndrome – could lead to an incapacitation of “healthy air” crewmember and also could be confused with hypoxia  Hyperventilation Carbon Dioxide (СО2) - chemoreceptors A small amount is dissolved in the plasma but majority is carried in chemical combination with water, as carbonic acid: СО2 + Н2О = Н2 СО3 and its subsequent dissociation into H+ and HCO3- ions. Central chemoreceptors in the reticular formation of the brain stem. Peripheral chemoreceptors - Aortic arch, - Bifurcation of the common carotid arteries (carotid sinus)  Hyperventilation Introduction (Cause and Effects) Excessive elimination of carbon dioxide than the body can produce leads to hypocapnia (reduced CO2 in the blood) If not compensated homeostatically – the blood pH will rise leading to respiratory alkalosis or the severe disorder of the acid-base state of the blood Dizziness, tingling in the lips, hands or feet, headache, weakness, fainting, and seizures  Hyperventilation (Mechanism) Introduction Amount of О2 increases by 40- Brain protects Level H2CO 3  itself from such 50% of initial Hypocapnia → an unconscious pH - shifts to the imbalance by Amount of CО2 in alkaline side (activity reducing blood of enzymes and vitamins circulation alveoli significantly changes) decreases (vasoconstriction)  Hyperventilation (symptoms) Introduction tingling sensations muscle spasms hot and cold sensations visual impairment dizziness unconsciousness ↑ CO2 => ↓ cardiovascular response => Recovery of consciousness Hyperventilation (symptoms) Introduction Because of the restricted blood flow to the brain associated with hyperventilation, it can produce symptoms that are similar to those of hypoxia  Hyperventilation (Similarity with Hypoxia Symptoms) Symptoms of hyperventilation and hypoxia Symptoms that occur with both hypoxia and hyperventilation Hyperventilation Hypoxia Dizziness Dizziness Light headed Light headed Blurred vision Blurred vision Numbness Numbness Tingling Tingling Muscle incoordination Muscle incoordination  Hyperventilation (How to Differentiate) Symptoms that occur with both hypoxia To help and differentiate between hyperventilation hypoxia and hyperventilation theses elements should be monitored - Flight altitude above 10,000 feet - possible hypoxia below 10,000 feet - probably hyperventilation - Cabin altitude - Oxygen system - Emotional state - Flight environment  Hyperventilation (Distinguishable Symptoms) Symptoms that occur with both hypoxia Hyperventilation and hyperventilation Hypoxia The onset of symptoms Hypoxia symptoms occur occurs gradually rapidly Muscle activity spastic Muscle soft and limp with little especially is upper extremities activity Causes skin to appear pale Skin may appear cyanotic and clammy  Hyperventilation (Prevention) The key to preventing hyperventilation is early recognition of signs and symptoms Monitor rate and depth of breathing Recognize stressors that would cause a person to over- breathe  Hyperventilation (In-flight Treatment) Symptoms that occur with both hypoxia Classic way is to make him/her breath into a paper bag and hyperventilation incorrect correct To don the oxygen mask To check that the oxygen regulator is on Ensure 100% oxygen is being delivered  Hyperventilation (In-flight Treatment) Symptoms that occur with both hypoxia Make sure that all connections are secured and hyperventilation Slow down rate and depth of breathing Descend to an altitude where hypoxia is unlikely to occur Dysbarism (Barotrauma) Dysbarism (Barotrauma) Syndrome resulting from the effects, of a pressure differential between the ambient barometric pressure and the pressure of gases within the body. Dysbarism (Barotrauma) Barotrauma is injury caused by expansion and contraction due to outside pressure changes, of air trapped in the cavities of the body. Occurs during ascent or descent. Most commonly affected body parts are middle ears, nose sinuses, teeths, intestines Barotrauma can cause discomfort or extreme pain sufficient to interfere with the pilot’s ability to operate the aircraft Dysbarism (Barotrauma) Boyle’s Law The volume of a gas is inversely proportional to its pressure when temperature remaining constant Dysbarism (Barotrauma) Gas Expansion DRY GAS EXPANSION WET GAS EXPANSION The atmosphere is In the body, gases are mainly a dry gas, saturated with water expanding under vapor. In equal conditions conditions of constant t (with altitude in (the same t, pressure, decreasing pressure, the altitude), the volume of volume of gas increases) wet gas is greater than dry.  Gas Expansion 6.0X 43,000 9.5X 4.0X 34,000 5.0X 2.5X 25,000 3.0X 1.8X 18,000 2.0X Anatomy of ear Semicircular Cochlea canal Auditory nerve Ear drum Middle ear Outer Ear Eustachian Opening to throat tube Eustachian tube Links the nasopharynx to the middle ear and helps in equalizing pressure across the eardrum Seldom problems happens in ascent Most problems occur in the descent when air attempt to return to the ear Eustachian tube The exit of the Eustachian tube into the nasopharynx opens as a throttle valve (unidirectional). Air easily escapes from the middle ear on ascent, but the valve prevents air to enter middle ear on descent, when it is necessary to equalize the increasing ambient pressure with lower pressure in the cavity of middle ear. Impact of the eardrum can cause severe pain Barotrauma of middle ear The severity of Otic Barotrauma depends upon the rate of climb or descent Mainly it occurs at lower altitudes where pressure changes are the greatest The problem is increased if the person has a cold or any other condition which has caused the mucous membrane lining the Eustachian tube to become inflated and swell Barotrauma of middle ear Differential pressure Symptoms 5 mm Hg Feeling of fulness in the ear 10-15 mm Hg Hearing loss 15-30 mm Hg Discomfort, tinnitus 30-100 mm Hg Pain, feeling unwell > 100 mm Hg Rupture of the tympanic membrane (eardrum) Pressure Effect Middle Ear Cavity Tympanic Membrane Atmospheric Pressure Outer Ear Clear Eustachian Tube Middle Ear Cavity Tympanic Membrane Atmospheric Pressure Ear block Outer Ear Eustachian Tube Blocked / Infected Barotrauma of middle ear Tympanic membrane, (ear drum), normal Barotrauma of middle ear Perforation of the tympanic membrane Barotrauma of middle ear: (investigations of ear function) Conductive hearing loss Rinne-Weber test - lateralization in the affected side Audiometry using pure tones - loss of hearing of high and mid tones Impedancemetry - detects obstruction of the Eustachian tubes Barotrauma of middle ear One or both ears can be affected and will cause: a) Pain (gradual or sudden) b) Temporary deafness c) Vertigo d) Tinnitus (a ringing in the ear) e) Eardrum rupture and bleeding in extreme cases. This may cause deafness Barotrauma of middle ear It is important that pilots ensure that having suffering from Otic Barotrauma they are 100% in a perfect state of health before returning to flying duties If the resumption of flying takes place prior to complete recovery, this can lead to further damage to the system which result in a chronic state and the risk of infection “Clearing the ears” Valsalva Manoeuvre – lowing down a held nose with the mouth closed. But a violent usage of this method may cause damage. Less severe methods are: Swallowing with the nose held Yawning Moving the lower jaw from side to side If all these methods fail, a landing should be made as soon a practical and medical assistance sought from an Aviation medical specialist Barotrauma of middle ear (prevention) Initial medical examination Application of Eustachian tube opening manoeuvres Refraining from flying in case of inflammatory diseases and infections of the upper respiratory tract. Cabin pressurization, control of the rate of cabin pressure change (about 300-500 feet per minute in the ascent, not faster than 300 feet per minute in the descent) The Sinuses Frontal Ethmoid Maxillary Sphenoid  The Sinuses Tiny ducts connecting the sinuses to the nose can become swollen or obstructed allowing air to become trapped within the sinuses Normally, there are no problems, they can easily vent air in the ascent and allow re-enter air in the descent, If the sinus or sinuses are inflamed - a sensation of pain occur The pain, often starts around the eyes, severely weakens the pilot, causes severe eye watering, making piloting impossible Bleeding from the nose may occur  Treatment of an Ear/Sinus Block Stop the descent of the aircraft and attempt to clear by Valsalva. If unable to clear, climb back to altitude until clear by pressure or Valsalva. Descend slowly and clear ear frequently during descent.  Barodontalgia (аerodontalgia ) Tooth pain occur due to air around and inside old or poorly applied fillings or abscesses: Gum abscess: dull pain on ascent Inflamed pulp: sharp pain on ascent Inflamed maxillary sinus: pain primarily on descent Gastro-intestinal Barotrauma Air is swallowed along with food or the digestive processes can themselves form gas If bubble of air collects in the stomach it can easily escape from the mouth The main problem is the gas in small intestines that will expand causing discomfort and sometimes pain sufficiently severe to cause fainting  Gas Expansion (prevention of pain) It is recommended to avoid: Food which are high gas producers (raw apples, cabbage, cucumbers, cauliflower, celery, bear, beans, spicy food) before flight, Eating quickly before flight Eating too much (swallowed air increases with each bite) Do not drink carbonated drinks, and a large amount of liquid before takeoff Do not chew gum before climbing Keep normal bowel function; Decompression sickness  Decompression sickness (DCS) Pathological condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurization - rapid transition from a high- pressure environment to one of lower pressure. Also called bends or caisson disease (bubbles can form in or migrate to any part of the body, DCS can produce many symptoms, and its effects may vary from joint pain and rashes to paralysis and death. Individual susceptibility can vary from day to day, and different individuals under the same conditions may be affected differently or not at all)  Cabin Pressurisation In 1875 three French aeronauts attempted a high altitude ascent in a free balloon called the Zenith. Insufficient knowledge of human physiology and the effects of high altitude contributed to a tragic accident. At 26,000 feet all 3 lost consciousness and only one survived when the balloon touched down Cabin Pressurisation In 1931 a pressurized cabin was first tried in the form of a gondola. In 1939, the first high altitude passenger carrying aircraft was developed as the Boeing 307 stratoliner Advantages of Pressurization Maintaining a safe and comfortable environment for human occupancy involves the simultaneous control of - Temperature - Air circulation - Humidity - Pressure An oxygen mask does not need to be worn Risk of Decompression Sickness is reduced There is less vibration and noise Better control of temperature and ventilation There are fewer trapped gas problems Disadvantages of Pressurization Structural - Increases the aircraft weight - Requires additional equipment o Engineering design (more complex) o Engine power (must be greater) o Airplane maintenance and control - Reduced payload capacity and maximum performance - Addition of control systems of air pollution (smoke, CO2, odors from the compressors...) Relative humidity Decompression - cold - hypoxia - disbarisms Mechanics of Pressurization Ambient air is introduced into a compressor - Compressed air rapidly heats Air is sent through a cooling unit Air is then introduced into the cabin Air departs cabin under the control of the out-flow valves - Out-flow valve allows the air to come in quicker than it leaves creating a high pressure environment  Pressurization Systems Isobaric - Most common system - Cabin altitude is preset and remains so throughout the flight Isobaric Differential - Used mainly in military fighter aircraft - Cabin will pressurize at a preset altitude - Once preset altitude is surpassed, a constant pressure differential is maintained Sealed Cabin - Used only in spacecraft - Carries it’s own supply of gases to create the pressure environment Cabin Pressurisation Cabin pressurization systems ensure that the effective altitude to which the occupants are actually exposed is much lower than of the one aircraft is flown. It ensures the effective pressure for the normal human’s vital activity Standard of ICAO at any altitude of the flight the pressure in cabin should not exceed the one at 8000 feet (2438m) The rate of pressure change is confined to: 500 ft/min – in the ascent 300 ft/min – in the descent Cabin decompression: Types of Pressurization Loss Slow decompression - loss of cabin pressurization can occur in flight, crew could make appropriate measures before passengers are aware of anything amiss and descend to a safety altitude and / or land. More than 10 seconds Gradual loss, easily unnoticed: Periodic checks of the instruments of pressure control If it occurs at >25.000 ft: DESCENT to 10.000 ft (if O2 is not available) or 25.000 ft Rapid decompression - Total loss of pressurization between 1 and 10 seconds: EMERGENCY PROCEDURE (O2; descent to safety level). Rare the rapid decompression may occur due to loss of a window or door or a failure in the fuselage. Passengers and crew members will experience: COLD, HYPOXIA, DECOMPRESSION Oxygen can be supplied but for only a limited period Explosive decompression - less than 1 second Cabin decompression The aircraft must rapidly descend to 10 000 ft or Minimum Safe Altitude (MSA) whichever is higher The pressure in cabin could be equalized with the pressure outside of aircraft very quickly It is mostly important - crew protection must be the highest of priorities. It is critical in decompression for the crew to don the oxygen mask and check the flow of О2 as quickly as possible. Life of all occupants depends on them. Factors of Decompression Rate Size of the opening Volume of the cabin Pressure differential Factors of Decompression Rate Pressure ratio Altitude - The higher the altitude the more severe the decompression physiologically Physical Characteristics of Decompression Noise Fog Flying debris Cooler Temperature - Frostbite and hypothermia Henry’s Law The amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid Decrease of partial pressure leads to the decrease of the amount of gas in the liquid consequently Cabin decompression Any ascent to altitude over 25 000 ft, is associated with DCS However DCS can happen at 18 000 – 25 000 ft DCS less possible below 14 000 ft Physiological Effects of Decompression Trapped gas expansion - Middle ear - Sinuses - Digestive Tract - Teeth Decompression Sickness Hypothermia Hypoxia Inflight Emergency Procedures Don Oxygen mask Maintain Aircraft Control Descend - 10,000 feet or lower Contributory factors to DCS Physiological Alcohol increases the risk Recent fractures and dislocations of the limbs Atrial Septal defect Body fat content Age – occurrence of DCS increases with age - risk at 40-45 years is 3 times higher than at19-25 years Gender – faster occurs in woman that in man Exercises increase the rate Contributory factors to DCS Physical Rate of decompression 8000 – 12000м (24000 – 36000ft) in 20-40 min Critical altitudes Rapid descent Duration of exposure Often ascent to altitudes (repeated exposure) Low temperature Pathogenesis Aeroembolism Formation of gas bubbles in the venous flow and vessels intersection Aeroembolism of adipose tissue vessels Aerotrombosis The deposition of blood cells on the bubbles Cerebral aeroembolism Pathogenesis 1 2 Gas bubble in the knee Diaphyseal lesions of the femurs: the joint 1 - necrosis without calcification; 2 - calcification necrosis Clinical symptoms Joints (in 60-70% cases) – Bends, the rheumatic- like pains in joints (shoulders, elbows, wrists, knees and ankles) N2 bubbles become trapped in the joints. Onset is mild, but eventually painful! Neurological (in 10-15% cases) The CNS – Staggers, the sufferer lose some mental functions, visual disturbance The PNS – Paresthesia, N2 bubbles form along nerve tracts. Tingling and itchy sensation and possibly a mottled red rash. Clinical symptoms Skin (10-15%) – the Creeps, feeling of a small colony of ants that are crawling over or under the skin Respiratory system (2%) – Chokes. N2 bubbles may get caught in the capillaries of the lung blocking the pulmonary blood flow. That leads to: serious shortness on breath, sense of suffocation accompanied by a burning, gnawing pain. Burning sensation in sternum. Uncontrollable desire to cough. Prevention of DCS 1 Limit of altitude - 25,000ft is recognized by experience 2 Limit time on staying at altitude - descent to a safe altitude and land at nearest location where qualified medical assistance is available. 3 Denitrogenation - removal of N2 by inspiration of 100% of О2 before ascent to altitude (military aviation) 4 Flights after diving (up to 10 meters or more) only in 24 hours Cabin pressurization 8000 ft or 2500 m Shall be in the cabin at any flight altitude  Type of aircraft Cabin altitude at flight level 350 (feet) В – 747 4 700 В – 737 8 000 DС – 10 5 400 A – 320 6 000 Concorde 1 000 At cruising FL Emb - 145 7 300 SAAB – 340 2 000 Flying and SCUBA* diving In scuba diving, the ambient pressure and consequently pressure in the body fluids rises, the amount of nitrogen increases (saturates the tissues), which is hardly released when the pressure decreases The quick ascent after diving is dangerous –small bubbles could expand and cause the onset of DCS Diving with the supply of compressed oxygen is dangerous. *SCUBA - self-contained underwater breathing apparatus Flying and scuba diving 760 mm Hg 1 atm Sea level 1 atm +1 атм = 2 атм 1 atm 30 ft (10 m) underwater Person at a depth of 30 ft (10 м) is exposed to pressure twice higher that at sea level => risk of DCS is already at 6 000 ft WARNING! Actions and treatment of DCS first action to be taken by a pilot in the event of a cabin decompression - to don oxygen mask and check oxygen flow Descend 100% 02 Land at nearest location where qualified medical assistance is available. Hyperbarotherapy (Compression greater than 1 atmosphere absolute). Treatment of cardio-vascular, respiratory and neuropogical symptoms Causes of decompression Structural Failure: Failure of a window, door, or pressure bulkhead for example, or in-flight explosion. An in-flight explosion may be due to a system failure, dangerous cargo, or a malicious act consequential on such as an explosive device on board. Pressurisation system failure: Malfunction of some part of the pressurisation system such as an outflow valve. Causes of decompression Inadvertent system control input(s): Accidental or incorrect activation of a critical pressurisation control. Deliberate Act: A drastic measure but one which an aircraft captain might consider, for example, as a way of clearing the cabin of smoke. Case of Decompression - COMET de Havilland DH106 Comet (British Overseas Airways Corporation) 10.01.1954 crashed in air, shortly after taking off from Rome en route to London (35 people on board) at altitude of 36000 ft. It was discovered that the stresses of metal around pressure cabin apertures were considerably higher than had been anticipated, particularly around sharp- cornered cut-outs, such as square windows that led to an explosive decompression. As a result, future jet airliners would feature windows with rounded corners – to eliminate a stress concentration. Thank you for your attention! Dr. Elena Cataman [email protected]