The Neurology of AltitudeThe Neurology of Altitude

Stephen J. McGirrStephen J. McGirr

Oregon Neurosurgery SpecialistsOregon Neurosurgery Specialists

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Layers of the AtmosphereLayers of the Atmosphere

•• TroposphereTroposphere–– Surface to 20,000 feetSurface to 20,000 feet

•• StratosphereStratosphere–– To 160,000 feetTo 160,000 feet

•• MesosphereMesosphere–– To 280,000 feetTo 280,000 feet

•• ThermosphereThermosphere–– to 350 milesto 350 miles

•• ExosphereExosphere

Oceanic pressureOceanic pressure

•• Every ten meters (33 Every ten meters (33 feet) of descent is feet) of descent is equivalent to gaining equivalent to gaining one atmosphere one atmosphere pressurepressure

Oceanic Temperature Oceanic Temperature

•• TemperatureTemperature

Relatively constant at surface down to 90 feetRelatively constant at surface down to 90 feet

Temperature drops rapidly at the thermoclineTemperature drops rapidly at the thermocline

Acute Decompression SicknessAcute Decompression Sickness“The Bends”“The Bends”

(aka “bubble trouble”)(aka “bubble trouble”)

•• Unexpected Unexpected depressurizationdepressurization

•• Flight or ascent after Flight or ascent after divingdiving

•• Nonpressurized flightNonpressurized flight

•• Rapid diving ascentRapid diving ascent

Acute Decompression SicknessAcute Decompression Sickness

•• Prevention: Be aware Prevention: Be aware of depth and duration of depth and duration of dive, and of ascent of dive, and of ascent raterate

Acute Decompression SicknessAcute Decompression Sickness

•• Neurologic symptoms:Neurologic symptoms:

Paresthesia, amnesia, visual changes, Paresthesia, amnesia, visual changes, behavioral changes, seizures, behavioral changes, seizures, unconsciousnessunconsciousness

Acute Decompression SicknessAcute Decompression Sickness

Symptoms by frequency (US Navy):Symptoms by frequency (US Navy):–– Local joint painLocal joint pain 89%89%

–– Arm symptomsArm symptoms 70%70%

–– Leg symptomsLeg symptoms 30%30%

–– DizzinessDizziness 5.3%5.3%

–– ParalysisParalysis 2.3%2.3%

–– Shortness of breathShortness of breath 1.6%1.6%

–– UnconsciousnessUnconsciousness 0.5%0.5%

Acute Decompression SicknessAcute Decompression Sickness

Treatment:Treatment:

Descend to or Descend to or remain at depth remain at depth until until equilibrated and equilibrated and ascend ascend appropriatelyappropriately

Nitrogen NarcosisNitrogen Narcosis

L’ivresse des grandes L’ivresse des grandes profondeurs profondeurs (“Rapture of the (“Rapture of the deep”) J. Cousteau, deep”) J. Cousteau, 19531953

Nitrogen NarcosisNitrogen Narcosis

Nitrogen, oxygen, and hydrogen cause Nitrogen, oxygen, and hydrogen cause decreases in mental function (as can the decreases in mental function (as can the noble gases, except helium and neon), but noble gases, except helium and neon), but the effect on psychomotor function is the effect on psychomotor function is inconsistentinconsistent

Carbon dioxide consistently causes a Carbon dioxide consistently causes a decrease in mental as well as decrease in mental as well as psychomotor functionpsychomotor function

Nitrogen NarcosisNitrogen Narcosis

•• MechanismMechanism–– Seems to be a direct effect of gas dissolving Seems to be a direct effect of gas dissolving

in nerve membrane with resultant disruption in nerve membrane with resultant disruption of transmissionof transmission

–– Causes an alteration in lipid bilayer Causes an alteration in lipid bilayer permeability to ion movement (similar to permeability to ion movement (similar to effect of ethanol)effect of ethanol)

–– The greater the lipid solubility, the less partial The greater the lipid solubility, the less partial pressure is neededpressure is needed

Nitrogen NarcosisNitrogen Narcosis

•• 00--3333 No symptomsNo symptoms

•• 3333--100100 Mild functional impairment, Mild functional impairment, mild euphoriamild euphoria

•• 100100--165165 Impaired reasoning, acalculia, Impaired reasoning, acalculia, overconfidenceoverconfidence

•• 165165--230230 Drowsiness, hallucinations, severe Drowsiness, hallucinations, severe response delayresponse delay

•• 230230--300300 Memory loss, stupefactionMemory loss, stupefaction

•• 300+300+ ManiaMania--depression, unconsciousness, depression, unconsciousness, deathdeath

Nitrogen NarcosisNitrogen Narcosis

•• The “martini law”The “martini law”

–– Every ten meters Every ten meters below 20 meters is below 20 meters is equivalent to one equivalent to one martinimartini

Nitrogen Narcosis: TreatmentNitrogen Narcosis: Treatment

•• Limit depth of diveLimit depth of dive

•• Utilize Trimix (helium, Utilize Trimix (helium, nitrogen oxygen) or nitrogen oxygen) or Heliox (helium, Heliox (helium, oxygen); this is oxygen); this is “technical diving” and “technical diving” and requires advanced requires advanced certificationcertification

High Pressure Neurologic SyndromeHigh Pressure Neurologic Syndrome

•• Occurs in commercial divers Occurs in commercial divers descending below 500 feet, descending below 500 feet, breathing helium oxygen breathing helium oxygen mix.mix.

•• “helium tremors” include “helium tremors” include myoclonic jerks, myoclonic jerks, somnolence, nausea, somnolence, nausea, dizziness and decreased dizziness and decreased mental performancemental performance

High Altitude Neurologic High Altitude Neurologic SyndromesSyndromes

•• Acute mountain sicknessAcute mountain sickness

•• High altitude cerebral High altitude cerebral edemaedema

•• High altitude headacheHigh altitude headache

•• Cerebral form of high Cerebral form of high altitude pulmonary altitude pulmonary edemaedema

•• Delayed neurologic Delayed neurologic decompression sicknessdecompression sickness

•• Other neurologic Other neurologic syndromessyndromes

High Altitude Cerebral EdemaHigh Altitude Cerebral Edema(HACE)(HACE)

•• Hypobaric hypoxiaHypobaric hypoxia

•• Includes acute Includes acute mountain sickness mountain sickness and acute and acute mountain mountain headacheheadache

Hypobaric hypoxiaHypobaric hypoxia•• Oxygen percentage (21%) stays the same, but pressure Oxygen percentage (21%) stays the same, but pressure

declines with altitudedeclines with altitude

•• Night vision deteriorates at 5,000 MSLNight vision deteriorates at 5,000 MSL

•• Above 12,000 MSL, judgment, memory alertness and Above 12,000 MSL, judgment, memory alertness and coordination become impairedcoordination become impaired

•• Deterioration can occur within 15 minutes at 15,000 feetDeterioration can occur within 15 minutes at 15,000 feet

•• Above 18,000 MSL decline occurs in <20 minutes; at Above 18,000 MSL decline occurs in <20 minutes; at 20,000 MSL, decline occurs in 520,000 MSL, decline occurs in 5--10 minutes10 minutes

•• Hypoxic changes worsened by alcohol, carbon monoxide, Hypoxic changes worsened by alcohol, carbon monoxide, anemia and certain medications (antihistamines, anemia and certain medications (antihistamines, sedatives, analgesics) and cold temperaturesedatives, analgesics) and cold temperature

HACEHACE

MechanismMechanism

–– Hypoxic cellular damage Hypoxic cellular damage with edemawith edema

–– Starts at 6500Starts at 6500--10,000 feet10,000 feet

–– Majority of people have Majority of people have symptoms at > 14,000 feetsymptoms at > 14,000 feet

SymptomsSymptoms

–– Confusion, nausea, Confusion, nausea, vomiting, fatigue, ataxia, vomiting, fatigue, ataxia, blindness, comablindness, coma

TreatmentTreatment

–– Descent, oxygen, diamox, Descent, oxygen, diamox, sildenafil, decadronsildenafil, decadron

Reversible Cerebral Vasoconstriction Reversible Cerebral Vasoconstriction SyndromeSyndrome

•• Caused by ascent to high altitudeCaused by ascent to high altitude

•• Severe headache with or without Severe headache with or without neurologic findings in the setting of neurologic findings in the setting of multifocal vasoconstriction of the cerebral multifocal vasoconstriction of the cerebral arteriesarteries

Other Neurologic SyndromesOther Neurologic Syndromes

•• VestibularVestibular–– Disturbances related to the cochleaDisturbances related to the cochlea

•• SomatosensorySomatosensory–– Disturbances related to the skin, joints and Disturbances related to the skin, joints and

musclesmuscles

•• VisualVisual–– Disturbances related to the eyes, and optic Disturbances related to the eyes, and optic

systemsystem

Vestibular dysfunctionVestibular dysfunction

•• MechanismMechanism

Vestibular IllusionsVestibular Illusions

•• The LeansThe Leans

•• Coriolis illusionCoriolis illusion

•• Graveyard spiralGraveyard spiral

•• Somatogravic illusionSomatogravic illusion

•• Inversion illusionInversion illusion

•• Elevator illusionElevator illusion

“Controlled Flight into Terrain”

Visual illusionsVisual illusions

•• False horizonFalse horizon

•• AutokinesisAutokinesis

•• Optical illusionsOptical illusions

–– Runway, Runway, featureless featureless terrain, haze, fogterrain, haze, fog

•• Night vision Night vision illusionsillusions

–– Autokinesis, false Autokinesis, false horizonhorizon

Thank you!Thank you!

“Captain” Doug McGirr (age 14)“Captain” Doug McGirr (age 14)