13-Feb-161High Atitude High Altitude Acclimatization

May 4, 2023May 4, 2023 11High AtitudeHigh Atitude

High AltitudeHigh Altitude

Acclimatization Acclimatization

May 4, 2023May 4, 2023 High AtitudeHigh Atitude 22

Hypoxia of High Hypoxia of High AltitudeAltitude

• As one ascends to high altitudes•One encounters problems associated

•Hypoxia, increased radiation & exposure to cold temp

• Basic cause of hypoxia•As altitude increases

•Barometric pressure falls•% Composition of air does not change

appreciably•Partial pressures of respiratory gases

fall


Hypoxia of High AltitudeHypoxia of High Altitude•At an altitude of 18,000 ft

(5,500 m)•Barometric pressure is ½

normal (380 mm Hg)•PO2 of moist inspired gas

•(380-47)*0.2093 = 70 mm Hg•Note kilimanjaro is at 19,360 ft


Hypoxia of High AltitudeHypoxia of High Altitude• At summit of Everest 29,028 ft

•Barometric pressure = 250 mm Hg•PO2 of moist inspired gas = 43 mm Hg

• At altitude of 63,000 ft•Barometric pressure =47 mm Hg

•PO2 of moist inspired gas = 0


Effect of High Altitude on Effect of High Altitude on Bar Pres and PBar Pres and PO2O2

Altitude (ft)

Pressure mm Hg

PO2 air

mm HgRemarks

63,000 47 1050,313 86 1840,000 141 30 Severe O2 lack despite

use of 100% O2

33,500 190 40 ¼ atmos, Mt Everest 29,028(250 mm Hg)

20,000 349 73 Danger to life unless O2 added to inspired air,

18,000 380 70 ½ atmos, Kili 19,36010,000 523 110 >12,000 definite O2 lack

0 760 159 Up to 8,000 safe zone


High Altitude Vs PHigh Altitude Vs PAO2AO2, , PPACO2ACO2, O, O2 2 Sat%Sat%

Altitude (ft)

Bar.Pres (mm

Hg)

PO2 in air (mm

Hg)

PAO2 (mm Hg)

PACO2 (mm Hg)

Art. O2 sat%

63,000 47 10 0 24 0

30,000 226 47 21 24 20

20,000 349 73 40 24 70

10,000 323 110 67 36 90

0 760 159 104 40 97


Hypoxia of High AltitudeHypoxia of High Altitude•Effect of CO2 & water vapor•Even at high altitude•CO2 production is still there•Water vaporizes in alveolar •Leading to dilution of alv O2

conc•PAO2 = (PB– PCO2 – 47)


Effect of Breathing Pure OEffect of Breathing Pure O22

•Space that was occupied by nitrogen• Is now occupied by oxygen•This improves the % saturation

of Hb with oxygen



Breathing air

Breathing 100% O2

Altitude Barr.Press

PAO2 mm Hg

% sat PAO2 mm Hg

% sat

30,000 21 30 139 99

40,000 12 15 58 87



• An aviator breathing oxygen in an un-pressurized aircraft– Can ascend to far higher altitudes

than one not breathing pure oxygen e.g 4700ft as compared to 23000ft which is a Limit for an un-acclimatized individual who is also breathing normal air


Effects of Breathing Pure OEffects of Breathing Pure O22

• When individual is breathing pure oxygen•Pao2 remains 90%

•Up to altitude of 39,000 ft• Falls to 50% at 47,000 ft

for unacclamatized falls to 50% at 23000ft


Effect of Acute HypoxiaEffect of Acute Hypoxia• Begin at about 12,000 ft

– Drowness, lastitude– Mental & muscle fatigue– Headaches, nausea– Euphoria

• Above 18,000 ft– Muscular twitches & convulsions

• Above 23,000– Coma, death


AcclimatizationAcclimatization•Respiratory• Increase in pulmonary

ventilation•Hyperventilation•Exposure to low PO2 stimulate

chemoreceptors•Stimulate respiration•Leads to 65% increase in alveolar

ventilation


AcclimatizationAcclimatization• An immediate compensation for

high altitude•Makes it possible for a person to

ascend several thousand feet• The in alv ventilation decrease

CO2 PCO2 & pH both

• Inhibit respiration•Tend to oppose stimulatory effect of

hypoxia


Acclimatization Acclimatization •After 2 to 5 days this

inhibition fades away–Ventilation 3 to 7 times the

normal level•Active pumping of HCO3

- from CSF•Cause pH in the CSF

– Chemoreceptors are once more stimulated


AcclimatizationAcclimatization• Haemoglobin

– Hypoxia causes– Release of erythropoietin– Increase production of RBC

(polycythemia)• Haematocrit increase

– From 40 –45% to 60-65%– Hb increase from 15 gm% to 22 gm

%


AcclimatizationAcclimatization• Total result is

– Increase in circulating Hb of 50 to 90% more than normal

• Polycythemia– Increase viscosity

• However, these adaptive changes– Slow to develop– Takes about 2 – 3 weeks– Become fully developed after many months


Acclimatization Acclimatization • O2 transport affinity of Hb for O2

– Effect of increased 2,3 DPG • (from 85 g/ml to 140 g/ml of blood)

within 1st 2 days•Shifts O2 - Hb dissociation curve to the

right• Diffusion capacity of lung for O2

(21 ml/mm Hg/min)– Increases 3 times more


AcclimatizationAcclimatization• Increased capillary density

The number of capillaries The distance between

capillary & cells


AcclimatizationAcclimatization• Cardiac output

– Increase by 20 – 30% immediately– But after few days

•Return back to normal•May fall slightly below normal after few

months• There is increase in blood flow to

– Muscles, heart, brain


AcclimatizationAcclimatization•Cellular level•Enzyme adaptation to

hypoxia– Increase in number of

mitochondria– Increase in cellular oxidative

enzymes


Failure to AcclimatizeFailure to Acclimatize• Chronic mountain sickness• After remaining at high altitudes

for a long time– One develops mountain sickness

• Red cell mass & haematocrit– Become exceptionally high

• Pulmonary arterial pressure– Become elevated more than during

acclimatization


Failure of Failure of AcclimatizationAcclimatization

•Right heart becomes greatly enlarged

•Peripheral arterial pressure falls

•Congestive heart failure develop


(II) Deep Sea Diving(II) Deep Sea Diving• Relationship of sea depth to

pressure• A column of fresh water 34 ft

(33 ft sea water) high– Exert the same pressure as the

atmosphere above earth– Person 33 ft beneath ocean

•Exposed to pressure of 2 atmospheres


Effect of Depth on Effect of Depth on PressurePressure

Sea depth (ft) Pressure (atmos)

O 1

33 2

66 3

100 4

200 7

400 13


Effect of Depth on Effect of Depth on Volume of GasesVolume of Gases

• Can be derived from gas laws• P1V1 = P2V2• Example if

– At sea level•P1 = 1 atmosphere, V1 = 1 liter

– At 33 ft below sea•P2 = 2 atmosphere, V2 = (P1V1)/P2 = ½ liter

• The air chambers of the divers will be compressed


Nitrogen NarcosisNitrogen Narcosis•About 4/5th of air is nitrogen•At sea level pressure–Nitrogen has no bad effect to

the body tissues•However, at high pressures–Nitrogen can cause varying

degree of narcosis


Nitrogen NarcosisNitrogen Narcosis• When a diver remains beneath

the sea – For about an hr breathing

compressed air• At 120 ft

– Begins to have symptoms of mild narcosis•Exhibit joviality•Becomes careless


Nitrogen NarcosisNitrogen Narcosis•At 150 - 200 ft–Becomes drowsy

•At 200 – 250 ft– Loss of strength–Clumsy

•Beyond 250 ft–Diver usually becomes useless


Nitrogen NarcosisNitrogen Narcosis• The narcosis is due to effects of

dissolved N2

– N2 diffuses freely through fat– Into nervous tissue– Alters conduction of nerve impulse– Decreases excitability

• Brain function becomes impaired


Oxygen ToxicityOxygen Toxicity• Effect of extremely high PO2• When the PO2 increase above 100

mm Hg– Amount of dissolved O2 in water

increases • The normal safe range of tissue PO2

– Is between 20 – 60 mm Hg• At higher tissue PO2

– Oxygen poisoning occurs


Acute Oxygen PoisoningAcute Oxygen Poisoning• Due to extremely high tissue PO2

– Exposure to 4 atmospheres pressure of O2•Partial pressure of about 3040 mm Hg

will cause– Seizures (convulsion) within 30 to 60 min

• They occur without warning• Likely to be lethal to the diver

•Other symptoms include– Nausea, muscle twitches, dizziness,

disturbances of vision, irritability


Oxygen PoisoningOxygen Poisoning•Excessive intra cellular

oxidation–Oxidizing free radicals

• Molecular O2 – Active form of O2

– Oxygen free radicals•Super- oxide free radical (O2

-)•Peroxide radicals (hydrogen peroxide)


Oxygen PoisoningOxygen Poisoning•At normal tissue PO2 –Small amount of free radicals

are formed–Body contain enzymes that

remove them•Peroxidases, catalases, superoxide dismutase


Oxygen PoisoningOxygen Poisoning•Above a critical level of

alveolar PO2 (>2 atmospheres)–Hb – O2 buffering mechanism fail–Tissue PO2 rise tremendously–The amount of oxidizing free

radicals


Oxygen PoisoningOxygen Poisoning• Effects of oxidizing free radicals

– Oxidize polyunsaturated fatty acids•Essential components of cell

membranes– Oxidize cellular enzymes

•Damage cellular metabolism• Nervous tissue

– Very susceptible– Lethal effect caused due to brain

damage


Decompression of DiverDecompression of Diver• When a diver breathes

compressed air for a long time– Amount of nitrogen dissolve in body

fluid increase• The nitrogen dissolved in tissue

– Not metabolized– Remains dissolve in tissue fluids


Nitrogen Dissolved in Nitrogen Dissolved in Body FluidBody Fluid

Depth in ft

Amount in

Liters0 1

33 2100 4200 7300 10


Decompression SicknessDecompression Sickness•Also known as–Bends–Compressed air sickness–Caisson’s disease–Diver’s paralysis–Dysbarism


Decompression SicknessDecompression Sickness• When a diver has been beneath the

sea for a long time– Large amount of nitrogen

•Become dissolved in body fluids– If the diver suddenly comes to the

surface•Significant amount of nitrogen bubbles

– Can develop in the body fluid•These can cause some damages

• This is known as decompression sickness


Decompression SicknessDecompression Sickness• Symptoms• Most of the symptoms are

caused by – Bubbles blocking blood vessels

•Air embolism• The symptoms include

– Pain in joints and limb muscles– Nervous symptoms

•Dizziness, paralysis, collapse


Decompression SicknessDecompression Sickness•The chokes caused by–Massive numbers of bubbles

plugging pulmonary capillaries•Shortness of breath•Severe pulmonary edema


Decompression Decompression ProceduresProcedures

• However, – If the diver is brought to surface

slowly– Dissolved N2 is eliminated through

the lung•Rapidly enough to prevent

decompression sickness– About 2/3rd of the total nitrogen is

liberated in 1 hr– And about 90% of the total in 6 hrs


Decompression Decompression ProceduresProcedures

•There are special time schedules–For decompression–Depending on the depth and

duration of the dive

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13-Feb-161High Atitude High Altitude Acclimatization