American Osteopathic College of Occupational and Preventive Medicine OMED 2012, San Diego, Tuesday, October 9, 2012
Physiological Altitude Threats: Outline Hypoxia, Trapped Gas, Decompression, etc • Physiology of Decompressive Stress • Respiratory Physiology • Hypoxia and necessary protection • Barotrauma • Aviation DCS • AGE
Lou Gilleran, MD, MPH, MSHS CAPT, MC (FS), USN
What is Pressure? Atmospheric Pressure
• From a microscopic point • Since the air (a gas) is a of view, gas pressure is fluid, the pressure force caused by the collisions of gas molecules on a acts in all directions, not surface. Each individual just downward. The collision provides a tiny pressure force pushing push on the surface that downward due to the it contacts. The sum total of all of these tiny forces weight of the air is the determines the air same as the pressure pressure. The physical force acting sideways and units for pressure is force even upward. per area.
Measurement of Pressure Composition Of The Atmosphere
• Nitrogen 78% 597.0 mm Hg One square inch column of air from • Oxygen 21% 159.0 mm Hg Sea level to space • Other gasses & H2O 1% 4.0 mm Hg 760.0 mm Hg @ Sea Level 760 29.92 mm Hg inches Hg 14.7 lbs.
Scale lbs Barometer Barometer
N-1 American Osteopathic College of Occupational and Preventive Medicine OMED 2012, San Diego, Tuesday, October 9, 2012
Atmospheric Human Operational Parameters “Shells” • Man is designed for terrestrial existence up to 10K’ Thermosphere – Troposphere defines this physiologic zone 80 km to space – Troposphere is where weather, clouds, winds have greatest affect Mesosphere • Adiabatic (Lapse) Rate defines temperature reduction 50 km - 80 km (56 miles above sea level) of 3.5°F/1,000 ft (6.4°C/km) of altitude increase Stratosphere 10 km - 50 km (35 miles above sea level) Troposphere Sea level -10 km (7 miles above sea level)
Life at Altitude O2 and Altitude
• Lack of O2 is a relatively ineffective stimulus and begins to occur at about pO2 of 60 mm Hg. Though the – Corresponds to about 10,000 ft. on room air and 39,000 ft. atmospheric on 100% O2. percentages of gases stay the same • 1st sign is usually increased tidal volume (depth of with increased respiration) “air hunger” altitude the “partial pressure” of gases • Elevated pCO is the primary stimulus for increased decreases at higher 2 respiratory rate altitudes Sea Level 18,000 ft
Physiological Responses at Altitude Pre-existing Cardiopulmonary Disease
1) At high altitudes there's less O2, therefore less dissolved O2 in the blood. • FAA allows Cabin Altitude up to 8k’ where PAO2 is ~65 and O2 Sat 90% in healthy. 2) The response is stimulation of peripheral chemoreceptors which send signals to respiratory drives. • Therapeutic O2 required if needed at baseline altitude. 3) Hyperventilation leads to Respiratory Alkalosis. – Recommended if unable to climb 1 flight of stairs or walk 150’ w/o rest or dyspnia and 4) Respiratory alkalosis shift the Hb dissociation curve to the left • CHF NYHA Class III-IV or baseline PaO2 <70mm Hg so that Hb can pick up O2 easier. • Angina CCS Class III-IV 5) The kidney responds to alkalosis by generating H ions and this • COPD PaO2 <70 will correct the pH back to normal. • Medications in carry-on!
N-2 American Osteopathic College of Occupational and Preventive Medicine OMED 2012, San Diego, Tuesday, October 9, 2012
At 10,000 feet, alveolar pO2 is about Physiologic Atmospheric Grouping 60 mm Hg. This is on the steep portion of the Physiologic Deficient Zone oxygen/hemoglobin 10, 000 – 50, 000 ft desaturation curve. Any additional climb in altitude without ______10,000 ft supplemental oxygen can result in the insidious onset of Physiological Zone Sea Level – 10,000 ft hypoxia for the aircrewman. Healthy individual fit without the aid of special protective equipment Oxygen-Hemoglobin Dissociation Curve
Aircraft Pressurization System Types
Purpose and Types • Conventional – used currently in all pressurized aircraft • To ensure safety and comfort for the crew and – increase cabin pressure via on-board compressor passengers • Pressurization schedules
• Sealed Cabin
Commercial aircraft cabins are required to be pressurized such that the cabin pressure is not – used in space vehicles to exceed an altitude of 8,000ft. – very high altitudes (80,000 ft)
Pressurization Systems Aircraft Pressurization
• Isobaric systems maintain a constant cabin altitude Advantages from a preselected altitude (generally from 2000- 8000 ft) up to the service ceiling of the aircraft. • Reduces possibility of: • Isobaric-differential systems maintain a constant – Hypoxia altitude until the pressure differential (usually 5psi) is – Decompression sickness reached and then the differential is maintained up to – Trapped gas problems the service ceiling of the aircraft. • Comfort / mobility / fatigue • Sealed Cabin systems are used only in spacecraft and • Cabin temperature control carry their own supply of gases to create • Communication environment.
N-3 American Osteopathic College of Occupational and Preventive Medicine OMED 2012, San Diego, Tuesday, October 9, 2012
Aircraft Pressurization Aircraft Pressurization Ambient Air Disadvantages
• Increased operating cost A/C Jet Engine Outlet Valve Unit Cabin • Added weight
• Reduced aircraft performance Overboard Bleed Air Vent • Risk of accidental pressure loss
What Happens When Pressure Fails? Physiological Effects of Decompression • Decompression • Rapid Decompression – Explosive Decompression (less than 1 sec) – Arterial Gas Embolism (AGE) – Rapid Decompression (between 1-10 sec) – Decompression Sickness(DCS) – Slow Decompression (greater than 10 sec) – Hypoxia The NAVY averages 90 events per year or 2.5 occurrences / – Trapped Gas Expansion (TGE) 100,000 flight hours • G.I. Tract • Ears • Factors Affecting Severity • Sinus – Volume of cabin • Lungs – Size of Opening • Slow – Pressure Differential/ Ratio – DCS – Flight Altitude – Hypoxia (Insidious)
Arterial Gas Embolism Operational Problems
• Leakage of air from the lungs to the • Noise: Hissing to Explosion pulmonary circulation. • Due to pressure – expansion of • Fog: May be mistaken for smoke; decreased lungs. visual environment • Pulmonary circulation goes right to • Flying debris, dust and dirt effect vision the brain. • Coronary artery embolization can • Temp changes: lead to myocardial infarction or • Sea Level 70 F dysrhythmia. • 25K 20 F • Cerebral artery emboli can cause • 35K - 67 F stroke or seizures • 50K - 67 F
N-4 American Osteopathic College of Occupational and Preventive Medicine OMED 2012, San Diego, Tuesday, October 9, 2012
Altitude Threat Protection POSITIVE PRESSURE BREATHING (PPB) • Cabin Pressurization System
0 to 8,000ft 8,000 to 24,500ft 24,500 to 50,000ft Aircraft ALT = Cabin ALT Cabin ALT = 8,000ft Cabin ALT = Differential Positive Pressure Breathing (PPB) is the delivery (Isobaric) 35,000ft Cabin at 14,500ft of a gas to the respiratory tract at a pressure greater than the ambient.
Intermittent PPB Based on the level of hypoxia considered operationally Pressure applied only during inspiration phase. acceptable. Used in SCUBA The Navy uses a minimal alveolar pO of 60 mm Hg TYPES of PPB REQUIREMENT for PPB2 Reached at 39,000 ft, breathing 100% O2. Continuous PPB Pressure applied throughout the breathing cycle PPB is an emergency condition in operational aircraft. Primary type used in Military aviation
Altitude Threat Protection RESPIRATORY EFFECTS of PPB • Supplemental Oxygen System-Regulators 1. Distension of lungs and chest 2. Increased Pulmonary Ventilation (+50%) 3. Intrapleural Pressure 4. Breathing Effort 5. Venous Pooling/Distension 6. Reduction of Effective Blood Volume
Increased PPB 7. Reduction in Cardiac Output (-30%)
Oxygen (O2)
N-5 American Osteopathic College of Occupational and Preventive Medicine OMED 2012, San Diego, Tuesday, October 9, 2012
Applications of PPB Disadvantages of PPB
The physiological ceiling is raised from 39,000 ft to 6,000 ft increase is fairly small 45,000 ft. Potential physiological problems In a sudden decompression (up to 50,000 ft) PPB can Reverses the normal breathing pattern - training required to be used to maintain consciousness in order to effect compensate an emergency descent. Fatiguing Communications become very difficult Applications in increased G-tolerance Can induce hyperventilation
Hypoxia Types Of Hypoxia
Definition
• State of oxygen deficiency in cells and Hypoxic tissues sufficient to cause impairment (Altitude) Histotoxic (Poisoning) of function. O2 O2 Hypemic • Hypoxemia refers specifically to a O2 (Blood) O2 deficiency of O2 in the blood and will Stagnant likely result in hypoxia (Pooling)
Hypoxic Hypoxia Hypemic Hypoxia Diminished O2 available to lungs Reduced O2 carrying capacity of blood Causes: Causes:
• Ascent to altitude
• Malfunctioning equipment Carbon Monoxide • Loss of cabin pressurization Anemia
• Improper O2 equipment usage
Sulfa Drugs Hemorrhage
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Carbon Monoxide Stagnant Hypoxia Pooling or reduced flow of blood, as seen in heart failure and cold Wear and deterioration of airframe seals and opening of seams environments increases susceptibility. This will allow exhaust fumes and toxic gases to infiltrate crew compartment. Can be caused by inactivity, restriction of movements Flight personnel effects – Carboxyhemoglobin (COHb) levels of 15-25% produce Or G-Forces (G-LOC) headache and nausea. With prolonged exposure, muscular weakness, dizziness, and confusion occur. – 25%, electrocardiographic changes, stupor, and eventual unconsciousness will occur.
Effect of G ForcesEffect Forces Histotoxic Hypoxia Inability of cells to take up or utilize oxygen from the bloodstream, despite physiologically normal delivery of oxygen to such cells and tissues. Gs • Alcohol
• Medication (Narcotics, etc)
• Cyanide
Normal Grey/black Out GLOC • CO also Hypemic Hypoxia cause
Factors Influencing Onset Rate Signs and Symptoms Objective Symptoms
• Cabin altitude •Increased respiration rate and depth •Cyanosis (may not be evident in anemia) • Rate of ascent •Pallor • Duration of exposure •Mental confusion •Poor judgment • Individual tolerance •Muscle twitching • Physical fitness and activity •Cold clammy skin
• Self imposed and environmental stress
N-7 American Osteopathic College of Occupational and Preventive Medicine OMED 2012, San Diego, Tuesday, October 9, 2012
Signs and Symptoms Subjective Symptoms Stages of Hypoxia
• Air Hunger • Euphoria • Indifferent Stage • Apprehension • Belligerence • Compensatory Stage • Fatigue • Blurred vision • Disturbance Stage • Nausea • Numbness • • Headache • Tingling Critical Stage • Dizziness • Hot and cold flashes
Indifferent Stage Compensatory Stage • Altitudes: • Altitudes: – Air: 0 - 10,000 feet Air: 10,000 - 15,000 feet 100% O : 39,000 - 42,000 feet – 100% O2: 34,000 - 39,000 feet 2
• Symptoms: decrease in night vision @ 4000 feet • Symptoms: impaired efficiency, drowsiness, • acuity poor judgment and decreased coordination • color perception
Disturbance Stage Critical Stage • Altitudes: • Altitudes Air: 15,000 - 20,000 feet
100% O2: 42,000 - 44,800 feet Air: 20,000 feet and above 100% O2: 44,800 feet and above
• Signs: loss of consciousness, convulsions and death
N-8 American Osteopathic College of Occupational and Preventive Medicine OMED 2012, San Diego, Tuesday, October 9, 2012
Time of Useful Consciousness (TUC) Expected Performance Times Effective Performance Time (EPT) FL 430 & above 9-12 seconds
The period of time from the loss of oxygen supply or FL 400 15 - 20 seconds exposure to an oxygen poor environment to the time FL 350 30 - 60 seconds when deliberate function is lost FL 300 1 - 2 minutes
FL 280 2 1/2 - 3 minutes
FL 250 3 - 5 minutes
FL 220 8 - 10 minutes
FL 180 20 - 30 minutes
Time off Oxygen
1 minute
2 minutes
3 minutes
4 minutes
5 minutes
6 minutes
put back on oxygen
Warning Treatment of Hypoxia
Effect of Rapid Decompression on TUC/EPT • Maximum oxygen under pressure • Connections check – check security • Breathe at a rate and depth slightly less Time of useful consciousness (TUC) from than normal until symptoms disappear. hypoxia can be reduced by as much as • Descent below 10,000 feet and land as soon as conditions permit. 30 to 50 percent following a rapid decompression
N-9 American Osteopathic College of Occupational and Preventive Medicine OMED 2012, San Diego, Tuesday, October 9, 2012
Oxygen Paradox Hyperventilation • • Temporary worsening of Definition: An abnormal increase in the rate hypoxia symptoms after and or depth of breathing. administration of 100% O2 • Causes: • Emotional Stress • Caused by physiological reaction to a sudden • Improper Pressure Breathing flood of oxygen rich • Altitude hypoxia blood • Primary Physiological Results • Very rare occurrence – Hypocapnia (loss of carbon dioxide [CO2]) • Remain on 100% O2 – Alkalosis (shift in pH balance)
HYPERVENTILATION - EFFECTS HYPERVENTILATION - EFFECTS
• Respiratory System • Central Nervous System – Brain protects itself against chemical imbalance of blood by restricting blood flow. – + - CO2 + H2OH2CO3 H + HCO3 – The combined effects of the vasoconstriction and dilation and the Bohr effect cause a stagnant – Direction of flow is determined by pCO2 hypoxia to the brain.
– Hyperventilation causes a decrease in pCO2 – This stagnant hypoxia can result in LOC (hypocapnia), therefore a decrease in H+ – The alkalosis leads to neuromuscular irritability – The result is alkalosis which can lead to spasms and tetany
HYPERVENTILATION - EFFECTS Hyperventilation Symptoms • Dizziness • Numbness • Cardiovascular System • Tightening of muscles • Coolness – The hypocapnia/alkalosis causes • Muscle tremors • peripheral vasodilation • Tingling • cerebral vasoconstriction • Faintness – • Vision impairment The result is a restriction in blood flow to the • Tetany brain • Slight nausea – The Bohr Effect Onset of symptoms slow and gradual; muscle • Shift of the oxyhemoglobin curve to the left activity spastic especially in upper extremities; skin • restricts oxygen off-loading in the brain is pale or clammy.
N-10 American Osteopathic College of Occupational and Preventive Medicine OMED 2012, San Diego, Tuesday, October 9, 2012
Treatment of Hyperventilation
• Maximum oxygen under pressure Wayne –April,1958 Aviation Med: 307-15 • Connections check – check security Hypoxia Hyperventilation Dizziness –18.0 %– Dizziness – 27% • Breathe at a rate and depth slightly less Visual Disturb –17.6% – Visual Disturb – 4.2% Lightheaded – 9.9% than normal until symptoms disappear. Hyperventilation vs.– Lightheaded Hypoxia – 26% Tingling – 6.0% • Descent below 10,000 feet and land as – Hot or Cold Flash –3%Tingling 15.7% soon as conditions permit. – Hot or Cold Flash –3%
BOTTOM LINE: Impossible to determine clinically w/o blood gas.
GENERAL RULE: If below 10K’ = Hyperventilation If above 10K’ = Hypoxia
Trapped Gas Expansion (TGE) Boyle’s Law Barotrauma • Causes • At constant temperature for a fixed mass, the absolute pressure and the volume of a gas are • Symptoms inversely proportional
• Prevention
• Treatment
Middle Ear Post Flight Ear Block
Cause of block — Blocked or constricted eustachian tube or upper respiratory infection (URI); usually occurs on descent
Treatment (Ascent) Yawning, Chew & Swallow
Treatment (Descent) Valsalva
Avoid valsalva on ascent and Stay ahead of pressure changes TREATMENT = Frequent Valsalva
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The Sinuses Warning:
• Onset rate of Sinus Squeeze (Block) may Frontal occur faster than Middle Ear problems. Ethmoids • Leaves little time for Sphenoids aircrew decision making • Sinus pain may be Maxillary incapacitating if pain severe enough.
If your sinuses become blocked by a cold, pressure can’t be equalized with altitude change and pain will result Treatment is to stop ascent or descent then follow protocol Prevention is better option!
Teeth Barodentalgia Gastrointestinal Tract
• Tooth pain normally occurs on ascent • Occurs on ascent when trapped gas • Causes: Caries or failing and/or illfitting expands dental repair/appliance; loose filling; • Treatment : abscess; swollen maxillary sinus (impacted wisdom tooth). – Start as soon as symptoms appear – Relieve gas by belching or passing • Treatment flatus –Descend – Position change / Massage affected area –Dental treatment – If problems continue, descend
Vasovagal Syncope: Prevention • Brief loss of consciousness caused by a sudden drop in your heart rate and blood pressure, which reduces blood flow to your brain. • Vagus nerve is overstimulated by parsympathetic nerves from abdominal organs and causes the body's blood vessels to dilate and the heart to slow down. This anti-adrenaline effect decreases the ability of the heart to pump blood upward to the brain against gravity.
N-12 American Osteopathic College of Occupational and Preventive Medicine OMED 2012, San Diego, Tuesday, October 9, 2012
Recommendations Intro to Decompression Sickness Gases In Solution – Henry’s Law At a constant temperature, the amount of a given gas • Watch Diet: Avoid foods that can cause excess dissolved in a given type and volume of liquid is directly gas formation such as cauliflower, broccoli, proportional to the partial pressure of that gas in equilibrium onions, cabbage and pumpkin. with that liquid. 29.92 in Hg • Avoid carbonated beverages or drinking rapidly before flight. 55.1 in Hg • Avoid chewing gum on ascent. Cola Cola
0.3 mm Hg CO2 1.2 mm Hg CO2 34 degrees C 34 degrees C
(1 atm = 101.3 kPa = 14.7 psi = 760 mm Hg = 29.92 in Hg)
Decompression Sickness Decompression Sickness (DCS)
• Decreased pressure • Rapid ascent or high • Joint Pain - Bends forms releases nitrogen. altitudes can result in • CNS disorders - Staggers • Under normal bubbles. circumstances, the body • Bubbles block blood • Lung Involvement - Chokes is able to “off-gas” the flow. excess nitrogen. • Venous Gas Embolism • Skin symptoms – Creeps (VGE) occurs commonly and is cleared by lung - rarely results in DCS
DCS is uncommon below 18,000 feet
Decompression Sickness Factors Symptoms
• Rate of ascent • Local Joint Pain 89% • Altitude • Leg 30% • Arm 70% • Time • Dizziness (The Staggers) 5.3% • Body Composition • Paralysis 2.3% • Age • Shortness of Breath 1.6% • Extreme Fatigue and Pain 1.3% • Activity • Collapse with unconsciousness 0.5% • Dehydration
• Previous injury
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DCS Incidence While Breathing 100% Delayed Decompression Sickness Oxygen
80% of delayed DCS cases occur within 1 hour of exposure.
Occasionally occur within 24 hours of exposure.
Haldane Equation
• Dissolved gas followed by Sea level - 760 mm Hg evolved gas. 18,000 ft - 380 mm Hg • 760:380 = 2:1 • Body could tolerate up to a 2:1 ratio. 30 FSW – 1520 mm Hg Sea level – 760 mm Hg • 1520:760 = 2:1 24 HOUR Restriction Between 30 FSW to 8,000 ft ? SCUBA and Flying 1520:545 = 2.8 : 1
Protection/Prevention Training
• Cabin pressurization (primary method)
• Denitrogenation (Preoxygenate 30 min+)
• Exercise during preoxygenation enhances denitrogenation process.
Hypoxia Symptoms are individualized and fairly consistent over time making hypoxia training a worthy endeavor for aircrew enabling early recognition and corrective action.
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Last scary thing
•Ebullism: Formation of gas bubbles in bodily fluids due to reduced pressure.
•A system of liquid & gas at equilibrium will result in vaporization of liquid to gas. Water pressure is 47mmHg and the PB at 60k’ is 47mmHg. Voila bubbles and their negative ramifications
•This is known as Armstrong’s line.
•Pressure suits as worn in high altitude surveillance aircraft and extravehicular space travel are required to prevent this potentially lethal ocurrence
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