High Altitude: Physiology

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High AltitudePhysiology Illness
Military Sports Medicine Fellowship
Every Warrior an Athlete

• Kevin deWeber, MD, FAAFP, FACSM
• COL, US Army
• Director, Military Sports Medicine Fellowship
• 2012

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Objectives

• Outline strategies to optimize exercise
  performance at altitude
• Review pathophysiology of high altitude illness
  (HAI)
• Review the types of HAI and how they are treated
• Review factors predisposing to HAI
• Discuss factors in return-to-altitude decisions
  after HAI

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Cuenca, Ecuador

• 8,400 ft (2560 m)

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Preview

• Acclimatization and slow ascent are powerful
  preventives for High Altitude Illness
• Acclimatize properly
• Spend 2-3 nights at 2500-3000m before ascent
• Slow ascent
• Ascend lt 500 m/day of sleeping altitude
• Rest day every 3-4 days
• Prophylactic meds advised if unable to comply
• Acetazolamide is powerful to prevent most HAI
• Dexamethasone powerfully treats serious HAI

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Preview RISK of HAI

• Low risk
• No prior h/o HAI and ascent to lt2800m (9180 ft)
• Taking gt 2 days to ascend to 2500-3000m
  (8200-9840 ft) AND sleeping altitude increases
  lt500m/d

Luks et al. Wilderness Medicine Society
consensus guidelines for prevention and
Treatment of acute altitude illness. Wilderness
Envir Med 2010.
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• Moderate risk of HAI
• Prior h/o AMS and ascending to 2500-2800m in 1
  day (8200-9180 ft)
• NO prior h/o AMS but ascending to gt2800m in 1
  day
• ALL ascending gt500m/d (sleep elev.) at gt3000m

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• High risk of HAI
• Prior h/o AMS and ascending to gt2800m in 1 day
• ALL with prior h/o HACE or HAPE
• ALL ascending to gt3500m (11480 ft) in 1 day
• ALL ascending gt500m/d (sleep elev.) at gt3500m
• Very rapid ascents (e.g. Mt. Kilamanjaro)

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Preview Prevention of HAI

• Moderate and High risk persons consider
  prophylactic meds
• PRIMARY Acetazolamide 125 mg bid
• Start 2d prior to ascent, stop 2-3d after summit
• Kids 2.5 mg/kg/d
• ALT Dexamethasone 2mg QID or 4mg BID
• Only if cant tolerate Acetazolamide
• Start day of ascent, stop 2-3d after summit
• Ibuprofen 600 mg tid (two studies)

Luks et al. Wilderness Medicine Society
consensus guidelines for prevention and
Treatment of acute altitude illness. Wilderness
Envir Med 2010.
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(No Transcript)
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Environment at high altitude(gt1500 m or 4920 ft)

• Barometric pressure decreases
• Partial pressure of oxygen decreases
• Hypobaric Hypoxia
• Lower alveolar O2 leads to lower SaO2

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Effects of High Altitude Exposure

• Decreased exercise capacity
• /- 1 decrease in VO2max per 100m above 1500m
• Individual variability
• MECHANISMS
• Peripheral hypoxia
• Cerebral hypoxia ? peripheral inhibition
• High altitude illness
• Individual variability

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Acclimatization bodys adaptation to hypobaric
hypoxia
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Acclimatization

• Immediate (minutes to hours)
• ? Sympathetic tone ? ? HR CO
• ? Ventilation ? ? PaO2 and ? PaCO2 ? ? pH
• Renal bicarbonate diuresis (to balance pH)
• ? Pulmonary artery pressure ? ? O2 absorption
• Delayed (days to weeks)
• Erythropoietin ? ? RBC production,
  hemoconcentration
• Remodeling of pulmonary arterioles

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Altitude Illnesses (Failure to Acclimatize)
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• Cerebral Syndromes
• Acute Mountain Sickness (AMS)
• High Altitude Cerebral Edema (HACE)
• mild AMS moderate AMS HACE
• Pulmonary Syndrome
• High Altitude Pulmonary Edema (HAPE)
• Importance
• HACE and HAPE can be fatal

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Acute Mountain Sickness (AMS)

• Occurs above 1500 m (4920 ft)
• More common above 2500 m
• Defined as HEADACHE plus one or more symptom
• Anorexia, nausea or vomiting
• Fatigue or weakness
• Dizziness or lightheadedness
• Difficulty sleeping
• Headache alone High-Altitude Headache
• Gabapentin, Acetazolamide, or Ibuprofen
  preventative
• J Neurol Neurosurg Psychiat 2008
• Cephalgia 2007
• Wilderness Environ Med 2010

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Effects of AMS on performance

• Mild annoyance only
• Moderate impaired concentration, memory,
  speech, and physical performance
• Can be disabling
• Subtle abnormalities visible on MRI
• Effects can last weeks

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High Altitude Cerebral Edema(HACE)

• AMS symptoms plus ALTERED L.O.C. and ATAXIA
• Other neuro findings possible
• Coma develops
• Death results if untreated
• Pathophysiology
• altered cerebral vascular permeability
• leads to brain swelling
• MRI cerebral edema,
• lesions of corpus callosum

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High Altitude Pulmonary Edema(HAPE)

• Defined by two pulmonary symptoms
• Cough, dyspnea at rest, exercise intolerance,
  chest tightness/congestion
• and two pulmonary signs
• Crackles, wheezing, cyanosis, tachypnea,
  tachycardia
• Most common cause of death among HAI
• 50 mortality rate if not treated quickly

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High Altitude Pulmonary Edema(HAPE)

• CXR findings
• Blotchy fluffy infiltrates
• Pathophysiology
• Hypoxia
• ? pulmonary artery hypertension
• alveolar damage
• ? edema and hemorrhage into alveoli

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Risk factors for HAI

• Rapid gain in altitude
• Prior history of HAI
• genetic factors involved
• Alcohol, sedatives
• Strenuous exercise
• HAPE cold ambient temperature, resp. infxn

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HAI Protective Factors

• Residence at elevation gt900 m (2950 ft)
• Slow gain in elevation
• lt500 m (1640 ft) per day in sleeping elevation
• Genetic factors
• Physical fitness NOT protective

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Treating HAIGeneral Principles

• Rest, halt ascent
• Descend
• Moderate AMS gt500 m (1640 ft)
• HACE/HAPE gt 1000 m (3280 ft)
• Oxygen if available (keep Pox gt90)
• Keep warm (esp. for HAPE)

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Treating HAIMedications

• Acetazolamide
• Speeds acclimatization
• Treats moderate AMS HACE
• Dose 125-250 mg BID
• Anti-emetics
• Non-narcotic analgesics

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Meds (cont.)

• Dexamethasone
• Decreases cerebral edema
• Treats moderate AMS and HACE
• Prevents AMS, HACE, HAPE
• Dose
• 8-16 mg/d in div doses

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Meds (cont.)

• Nifedipine
• Decreases pulmonary artery pressure
• Prevents HAPE
• Dose 30 mg SR BID (one study)
• NOT EFFECTIVE FOR TREATMENT (one study)

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Meds (cont.)

• Salmeterol
• Decreases alveolar fluid transport
• May prevent HAPE
• Dose 125 mcg inhaled BID

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Meds (cont.)

• Tadalafil
• Dilates pulmonary vessels, prevents pulmonary
  hypertension
• May prevent HAPE
• Dose 10 mg po BID

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Treatment of AMS

• Descend gt 500 m (1640 ft) OR
• Rest 1-2 days at same altitude
• Oxygen 12-24 hours, if available
• Symptomatic treatment with analgesics,
  anti-emetics
• Consider acetazolamide 125-250 mg po BID

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Treatment of HACE

• Immediate descent gt 1000 m and hospitalize
• Oxygen to maintain SaO2 gt90
• Dexamethasone8 mg PO/IM/IV initially followed by
  4 mg QID
• Consider adding acetazolamide
• Portable hyperbaric therapy if descent impossible

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Portable Hyperbaric Chambers
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Treatment of HAPE

• Immediate descent gt1000 m
• Oxygen to keep SaO2 gt90.
• If descent/O2 not immediately available
• Portable hyperbaric therapy
• Nifedipine 30 mg extended release BID (avoid if
  concomitant HACE) and
• Salmeterol 125 mcg inhaled

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PREVENTION OFHAI
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Prevention of HAIGeneral Principles

• Proper acclimatization protocols are paramount
• Avoid abrupt ascent to gt3000 m (9843 ft)
• Spend 2-3 nights at 2500-3000 m before ascending
  further
• Ascend no more than 500 m (1640 ft) per day in
  sleeping altitude when gt2500 m (8200 ft)
• Rest day every 3-4 days

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Prevention of HAIOther protective factors

• Living at altitude gt2200 m days to weeks
• gt5days above 3000m last 2 months --gt less AMS
  (Schneider et al, MSSE 2002)
• Intermittent Hypoxic Exposure (IHE) 4hr/d x15d ?
  less AMS _at_4300 m
• Beidleman et al, Clin Sci 2004

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Prevention of HAIFIRST DETERMINE RISK

• Low risk
• No prior h/o HAI and ascent to lt2800m (9180 ft)
• Taking gt 2 days to ascend to 2500-3000m
  (8200-9840 ft) AND sleeping altitude increases
  lt500m/d

Luks et al. Wilderness Medicine Society
consensus guidelines for prevention and
Treatment of acute altitude illness. Wilderness
Envir Med 2010.
37
Cuenca, Ecuador

• 8,400 ft (2560 m)

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• Moderate risk of HAI
• Prior h/o AMS and ascending to 2500-2800m in 1
  day (8200-9180 ft)
• NO prior h/o AMS but ascending to gt2800m in 1
  day
• ALL ascending gt500m/d (sleep elev.) at gt3000m

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• High risk of HAI
• Prior h/o AMS and ascending to gt2800m in 1 day
• ALL with prior h/o HACE or HAPE
• ALL ascending to gt3500m (11480 ft) in 1 day
• ALL ascending gt500m/d (sleep elev.) at gt3500m
• Very rapid ascents (e.g. Mt. Kilamanjaro)

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Prevention of AMS/HACE

• Moderate and High risk persons consider
  prophylactic meds
• PRIMARY Acetazolamide 125 mg bid
• Start 2d prior to ascent, stop 2-3d after summit
• Kids 2.5 mg/kg/d
• ALT Dexamethasone 2mg QID or 4mg BID
• Only if cant tolerate Acetazolamide
• Start day of ascent, stop 2-3d after summit
• Ibuprofen 600 mg tid (two studies)

Luks et al. Wilderness Medicine Society
consensus guidelines for prevention and
Treatment of acute altitude illness. Wilderness
Envir Med 2010.
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Prevention of AMS/HACE SPECIAL SCENARIOS

• Military Ops requiring exertion and gt3500m
• Dexamethasone (also increases VO2max)

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Prevention of HAPE

• ALL ascent/rest precautions
• Moderate/High risk consider meds
• PRIMARY Acetazolamide 125 mg BID
• PRIOR HAPE Nifedipine 60 mg SR daily
  Salmeterol 125 mcg BID
• ALTERNATE Tadalafil 10 mg BID or Dexamethasone
  16 mg/d divided doses

Luks et al. Wilderness Medicine Society
consensus guidelines for prevention and
Treatment of acute altitude illness. Wilderness
Envir Med 2010.
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Considerations for high-altitude activities in
those with prior HAI

• Risk level
• Severity and type of prior HAI
• Ascent requirements
• Feasibility of descent/extra rest days if needed
• Availability of medical treatments

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Questions?