Altitude Physics Atmosphere

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AltitudePhysicsAtmosphere
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Altitude

• High altitude 1500 3500 m
• Very high altitude 3500 5500 m
• Extreme altitude above 5500 m

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Physics and atmospheric conditions

• Barometric pressure
• Torricelli (1644)
• We live submerged at the bottom of an ocean of
  the element air
• Pascal (1648)
• fall in pressure with increasing altitude (Puy de
  Dôme 1463 m)

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Barometric pressure

• Standard atmosphere (ICAO)
• Accurate for calculations in aviation
• Factors affecting air pressure
• Temperature
• Latitude
• Season
• Humidity

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Effects of latitude

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Seasonal changes

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Latitude and season
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Acclimatization
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Normal acclimatization

• Heart rate ?
• Breath rate ?
• Exhausted/breathless on exercise
• Hungry
• Urine output ?
• Sleep
• Headache

• All symptoms should disappear or get better after
  rest, food and water

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Acute mountain sickness

• Mild
• Moderate
• Severe

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Symptoms of mild AMS

• Headache
• Malaise
• Anorexia

• Nausea/vomiting
• Dizziness
• Dyspnea on exertion
• Dry cough
• Inner chill
• Low urine output

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Any symptom of AMS should be considered due to
altitude unless proven otherwise.
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What else could it be?

• Viral illness (muscle pain, myalgia)
• Hangover
• Exhaustion
• Dehydration
• Hypothermia
• Sedative or hypnotic medication
• Carbon monoxide

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Natural history of AMS

• Usually self-limiting
• If untreated may persist for weeks
• May progress to moderate and severe forms of AMS
  or to death
• Responds well to treatment

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Moderate AMS

• ATAXIA
• Single most useful sign for deterioration
• Lassitude
• Strange behaviour
• Confusion
• Impaired judgement
• Consciousness level ? ? coma
• Shortness of breath

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Physical findings
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Management of moderate AMS

• Stay at altitude, do NOT go further
• Descend if symptoms do not improve or get worse
• Drugs
• Give oxygen if available
• Use hyperbaric bag
• (may progress to severe AMS)

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If in doubt,go down.
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Measurements

• Resting pulse rate
• Oxygen saturation (SpO2)
• normal 88 95 at 5000 m

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Pulse rate

• Where and how?
• What is normal?
• at low altitude
• at high altitude

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Oxygen saturation

• Pulse oxymeter
• Measurement for O2 bound to haemoglobin
• Infrared light is absorbed by haemoglobin
• Normal values
• low altitude ? 95
• high altitude ? 90

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Severe AMS

• HACE or HAPE
• High altitude cerebral oedema
• High altitude pulmonary oedema

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Brain

• Brain needs oxygen
• Cerebral blood flow (normally 15 of cardiac
  output) will increase to 24
• Brain vessels dilate
• Volume cannot expand

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HACEHigh altitude cerebral oedema

• Treatment
• descent, descent, descent
• oxygen
• dexamethasone

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HAPEHigh altitude pulmonary oedema

• Caused by pulmonary vasoconstriction
• Treatment
• descent, descent, descent
• oxygen
• hyperbaric chamber
• nifedipine

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Management of severe AMS

• Organize descent by all means
• Give oxygen (0.5 1 l/min.)
• Hyperbaric chamber

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Medical treatment

• Acetazolamide
• Dexamethasone
• Nifedipine
• Oxygen

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Non medical treatment

• Descent
• Hyperbaric chamber

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Prophylaxis

• Rate of ascent (300 - 600m daily altitude gain)
• Medical prophylaxis

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Medical prophylaxis

• Acetazolamide (Diamox)
• Gingko Biloba
• Coca
• Anti asthmatic medication
• (Dexamethasone)
• (Oxygen)

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Acetazolamide Diamox

• Carbonic anhydrase inhibitor
• Alkalosis (due to hyperventilation) ? normal pH ?
  respiration ?
• Diuretic
• Side effects
• water loss, tingling, sulphur allergies,
  carbonated drinks

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Acetazolamide

• Dosage for prophylactic use
• 125 mg twice daily
• start the day before the ascent
• NB acetazolamide does not mask the symptoms of
  altitude sickness

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Gingko biloba

• Might be useful
• Recent studies suggest benefit at altitude
• possible alternative to acetazolamide for people
  with sulphur allergie
• Dosage 60 mg three times/day

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Coca

• South american locals chew coca leaves
• Exact mechanism not known
• Seems to be useful

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Anti asthmatic medication

• Seems to improve ventilation
• long term studies still pending
• (what about asthmatics at altitude)

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Oxygen

• Oxygen enriched air
• 21 ? 28 (5000 m ? 3000 m)
• CO2 - extraktion
• Monitoring of O2 and CO2
• ?system failure?
• Via face mask (ca. 2 l/min.)

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Treatment of AMS

• Descent
• Acetazolamide
• Dexamethasone
• Nifedipine
• Oxygen
• Hyperbaric bag

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Acetazolamide

• Dosage 250 mg (2 - 3 times/daily)
• useful for mild-moderate AMS

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Dexamethasone

• Very potent steroid
• HACE (temporary use only)
• Improves symptoms without improving
  acclimatization
• 8 mg, then 4 mg every 6 hours
• Do not ascent while on dexamethasone

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Nifedipine

• Useful in HAPE
• Lowers blood pressure in the lungs
• 10 mg (3 - 4 times/day)
• potent medication for high blood pressure

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Oxygen

• Via face mask (ca. 2 - 4 l/min.)

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Hyperbaric bag

• Portable bag inflated to 100 to 120 mmHG
• Simulates lower altitude
• Temporary measure to improve AMS-Victim, if
  descent is impossible

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Physiology at altitude
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Oxygen21 of ambient air at all altitudes

• Sea level
• Barom. Pressure1013 mbar
• Part. press. of O2212 mbar
• Number of O2-molecules per liter X

• 5000 m
• Barom. pressure 500 mbar
• Part. press. of O2100 mbar
• No. of O2-molecules per liter ½X

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Respiration normal values

• RR (respiratory rate)
• 10 12/min.
• TV (tidal volume), volume/breath
• 500 700 ml
• MV (minute volume)
• 6000 ml/min 60 000ml/min

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Respiration

• Basic calculations
• RR x TV MV
• 10 x 600 6000 ml Air
• 21 O2 1200 ml O2 (X molecules)
• 5000 m same minute volume but 50 oxygen
  molecules

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How do we compensate for this when going to high
altitude?

• Ventilation - lungs
• Circulation - heart, blood, vessels
• Tissues - O2-transport
• Kidneys
• Brain

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Ventilation

• Increase in depth and frequency
• Carotid body and breathing center
• Hypoxic ventilatory response (HVR)
• Caffeine, coca
• Alcohol, sleeping tablets
• Short terme acclimatization
• hyperventilation

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Ventilation

• O2-uptake ?
• CO2 -output ?
• Acid-base-balance shift
• Alkalosis
• NB Hyperventilation persists at return to sea
  level

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Long term acclimatization

• HVR ? blunted response to hypoxia
• alkalosis is not as severe
• ? Hyperventilation on exercise is not as remarked
  as in the visiting population

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Oxygen uptake and transport

• O2 uptake max 4.6 l/min. at low altitude 2.3
  l/min at 6300 m
• Oxygen
• Diffusion from air to blood (lungs)
• Bound to haemoglobin
• Physically dissolved in plasma

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Oxygen transport

• Lungs ? heart ? tissues
• Guided by tissue needs (heart, brain, kidneys)
• Muscles according to activity
• Muscle tissue reorganistion
• Diffusion distance ? (long term increased
  vascularisation)

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Hyperventilation

• high energy expenditure for ventilation
• RR
• Flow increases ? turbulent flow, despite thinner
  air
• Airway resistance ?

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Circulation

• Heart
• Blood and blood vessels

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Heart

• Heart rate and stroke volume increases
• Initially, returns to near normal values after
  some days
• Cardiac output increases initially
• decreases later (possibly protecting the heart
  function less work, less O2-requirement)

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Blood

• Cells
• Vessels

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Blood cells

• White and red
• Red blood cells will increase
• erythropoetin (kidney)
• oxygen transport capacity
• viscosity

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Vessels

• Lung vessels will constrict when hypoxic
• Hypoxic pulmonary vasoconstriction

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Brain vessels

• Brain needs oxygen
• Cerebral blood flow (normally 15 of cardiac
  output) will increase to 24
• Brain vessels dilate

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Kidneys

• Hyperventilation causes CO2 to decrease, which
  leads to alkalosis
• To compensate for alkalosis the kidney excretes
  water and bicarbonate
• Alkalosis ? normal pH ? ventilation ?

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Brain

• O2 ? ? vasodilation to provide more blood and O2
• CO2 ? ? alkalosis, which causes cerebral
  vasoconstriction
• Effect CBF ? (by 20 (2 3 days)
• Intracranial pressure increases

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Factors affecting acclimatization

• Age
• Gender
• Smoker/nonsmoker
• Fitness (marathon runner ?)
• Alcohol
• Pregnancy

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Other medical problems at altitude

• Thrombosis
• Peripheral oedema
• High altitude retinopathy
• HAFE high altitude flatus
• Pharyngitis/bronchitis
• Immune suppression
• Tooth ache

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Thrombosis

• Caused by high blood viscosity
• Potentially dangerous
• Get varicous veins treated

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Peripheral oedema

• Swelling of hand and feet
• no sign of AMS
• disapears generally at night

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High altitude retinopathy

• Bleeding at retina
• Visual impairment
• Usually not permanent

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HAFE high altitude flatus

• Expanding bowel gases at altitude
• Irritating to your partners

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Pharyngitis/bronchitis

• Cause by dry altitude air
• Throat lozenges

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Immune suppression

• Skin scratches, small wounds do not heal well
• Keep skin well protected
• Super glue

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Tooth ache

• Can worsen at altitude
• Expanding air in cavities
• Check with your dentist before going to altitude

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Other altitude related hazards

• UV-radiation
• Infrared radiation
• Reduced humidity
• Sudden climate changes

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UV - Radiation

• Increases by 4 per 300 m altitude gain
• Risks sunburn (UV-A), skin cancer (UV-B)dermal
  phototoxicity, snow blindness

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Infrared Radiation

• Heat related problems are generally
  underestimated
• Heat stroke (humidity ?, dehydration)

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Reduced humidity

• Irritates airways
• Dry cough
• Treatment lozenges

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Sudden climate changes

• Day/night temperatures
• Thunderstorms
• Lightning
• Shadow/sunlight temperature differences
• Snow fall
• Wind chill

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Medical disease and altitude

• Diabetes
• Asthma
• Chronic heart failure
• Cardiac arrhythmias
• High blood pressure
• Epilepsia

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Diabetes

• Well controlled
• Check the accuracy of blood sugar measurements
• Be aware of higher calorie needs at altitude for
  respiration
• Make sure your partners know what to do

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Asthma

• Well controlled
• Enough medication

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Heart disease

• Arrhythmias are generally no problem
• Heart failure, depends on severity
• Previous heart attack, but know fit, is no
  problem
• Assessment of fitness bycicle ECG test

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High blood pressure

• Well controlled
• Adjust medication
• Often slightly elevated blood pressure returns to
  normal at moderate altitude

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Epilepsia

• Can be a problem
• Hypoxia can cause epileptic seizures

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Performance at altitude
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General fitness

• It helps to be fit
• After acclimatization the fit at low altitude
  will be fit at high altitude, but he will be less
  fit than at low altitude.

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Muscle power

• Decreases with time at altitude
• General physical work load decreases

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Cerebral function

• Studies at American Medical Research Expedition
  1981 (Mount Everest)
• Impaired sensory, perceptual and motor
  performance
• Lethargic behavior with cerebral hypoxia
• EEG shows cortical depression

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Motor function

• SpO2 ?85 decreases capacity for mental
  concentration and abolishes fine motor
  coordination
• SpO2 ?75 leads to faulty judgement, emotional
  lability and impaired muscle function

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Verbal learning and memory

• Short term and long term memory declined at
  altitude

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Finger tapping test

• Performance declined at altitude
• Performance did not recover for more than 1 year
  (mountaineers on Mt. Everest)

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Aphasia screening test

• Expressive language errors increased
  significantly

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Long term effects

• After up to 221 days at 5100 mNo permanent
  cerebral dysfunction