aviation, high altitude and space physiology · 2019-08-21 · at high altitude decrease in oxygen...
TRANSCRIPT
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AVIATION, HIGH ALTITUDE AND SPACE PHYSIOLOGY
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Why P02 decreases at high
altitude???
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AT HIGH ALTITUDE
↓ barometric pressure
Barometric pressure of 760mmHg at sea level fall to-------------------------253 mmHg at mount Everest
↓P02 in alveoli
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Acute Effects Of Hypoxia
• Drowsiness• Mental and muscle
fatigue• Headache• Nausea• Euphoria
Further increase in altitude;
Twitching and seizuresComa or death.
• Decrease judgment and memory
• Inability to perform fine motor movement
• Decrease work capacity of cardiac and skeletal muscles.
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AT HIGH ALTITUDE
Decrease in Oxygen saturation
At 10000 feet-----arterial O2 saturation remain 90%
But at 20000 feet----02 saturation fall to 70% and
so on.
At 39000 feet-----arterial O2 saturation remain 90%
But at 47000 feet----02 saturation fall to 50%.
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What is the effect of breathing pure oxygen
on P02??
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PAO2=(PB−PH2O)FiO2−(PaCO2)
• PB is the barometric pressure
• PH2O (usually 47mmHg),
• FiO2 is the fractional concentration of inspired oxygen(0.21 if breathing air and 1 if breathing pure oxygen),
• PaC02(40mmHg)
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PAO2=(PB−PH2O)FiO2−(PaCO2)
At sea level; breathing air
PAO2=(760−47)0.21−(40)
Pa02=109mmHg
At sea level; breathing pure oxygen
PAO2=(760−47)1−(40)
Pa02=673mmHg
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ACCLIMATIZATION
• A person remain at high altitude for days, weeks or for years become more and more acclimatized to low PO2 ,so cause few delirious effects on body.
• After acclimatization person is able to work harder or ascend to still higher altitudes without hypoxic effects.
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How acclimatization to low PO2 occur???
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Hypoxia/↓ O2 availability
Stimulate chemoreceptors
Stimulate dorsal respiratory center
of medulla
↑ 𝐩𝐮𝐥𝐦𝐨𝐧𝐚𝐫𝐲𝐯𝐞𝐧𝐭𝐢𝐥𝐚𝐭𝐢𝐨𝐧
↓ PCO2 + ↑PH of body fluid
(respiratory alkalosis)
This is compensated by
kidney;
• ↓ H ion secretion
• ↑ Bicarbonate excretion
↓ Bicarbonate concentration in
CSF and brain tissues
↓ PH of fluid surrounding
chemo sensitive neurons of
respiratory center
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Hypoxia/↓ O2 availability
Stimulate Hypoxic inducible factors HIF (master switch)/DNA binding transcription factor
Activate genes
Erythropoietin genes
↑RBC production
↑Hemoglobin con.
Vascular and endothelial
growth factor genes
Angiogenesis
↑no. of systemic
circulatory capillaries
Increase blood volume
Mitochondrial genes
↑Cellular mitochondria
Glycolytic genes
↑Cell ability to use O2 despite ↓PO2.
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Hypoxia/↓ O2 availability
Stimulate Hypoxic inducible factors HIF (master switch)/DNA binding transcription factor
Activate genes
↑Nitric oxide availability
Pulmonary vasodilation
Pooling of blood
Expand capillaries
↑ O2 diffusing capacity
↑surface area
↑hydrostatic pressure
↑ pulmonary arterial blood
pressure
Force blood into large no. of capillaries
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Hypoxia/↓ O2 availability
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• Acclimatization of natives of high altitude is superior to lowlanders in all aspects because of these additional factors;
• Increase chest size.
• Increase COP
• Increase hemoglobin
ALL THESE FACTORS FAVOURS EFFECTIVE OXYGEN TRANSPORT DESPITE OF LOW PO2.
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• Native persons of high altitude daily work output = low landers at sea level
But;• Even well acclimatized lowlander can never
have same workout when compared with native.
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ACUTE MOUNTAIN SICKNESS
Rapid ascend to high altitude more than 8000 feet
HYPOXIA within hrs. to about 2 days
Local vasodilation of cerebral blood vessels
Blood flow into capillaries
↑Capillary pressure
Fluid leakage into cerebral tissues
Cerebral edema
Pulmonary arterial vasoconstriction
Force blood into unconstricted vessels
↑ Capillary pressure
Fluid leakage into pulmonary tissues
Pulmonary edema
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CHRONIC MOUNTAIN SICKNESS
A person remain at high altitude for long time(1 year)
Increase RBC + hematocrit
Pulmonary arterial
vasoconstriction
Increase blood viscosity
Decrease blood flow to tissues
Decrease oxygen delivery
Increase pulmonary
arterial pressure+
Right side of heart enlarge
+Congestive heart
failure
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Acute mountain sickness Chronic mountain sickness
Rapid ascend to high altitude(8000 feet)
A person remain at high altitude for long time
Symptoms appear within hrs. to about 2 days
Symptoms appear gradually (appr. 1 year)
Symptoms of hypoxia Symptoms of hypoxia
Pathogenesis::::Increase altitude-----decrease P02-----Hypoxia
Pathogenesis::::Increase RBC + hematocrit--------Increase blood viscosity------Decrease blood flow to tissues----decreaseoxygen delivery-----hypoxia
Complications are cerebral and pulmonary edema
Increase pulmonary arterial pressure which then lead to Heart failure is main complication
Move person to low altitudeGive pure oxygen
Move person to low altitude
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AVIATION PHYSIOLOGY
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F = mv2
r
F-- centrifugal accelerating force
• Increase velocity-----increase force
• Sharp turn----increase force
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Effect of centrifugal accelerating force on the body (positive G)
• Increase pressure in veins of feet.
• Pooling of blood in lower part of body.
• Decrease COP.
• Decrease systolic and diastolic blood pressure.(but for initial few minutes—after that recovered by activation of baroreceptor reflex).
• If acceleration is more----black out of vision followed by unconsciousness.
• Extremely high accelerating force-----fracture of vertebrae(more than 20G)
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• Hyperemia of head.
• Brain edema.
• Psychotic disturbances.
• Eyes often temporarily blinded with red outs.
• Increase cerebral blood pressure----cause small blood vessels on surface of head and in brain to rupture(not cranial blood vessels which are protected by cushioning effect of CSF).
Effect of decelerating force on the body (Negative G)
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Protection of body against centrifugal accelerating forces
• Tightening of abdominal muscles + Leaning forward to compress abdominal muscles------prevent pooling of blood in large vessels of abdomen.
• Special anti G suits for abdomen and leg----------prevent pooling of blood.
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Space craft
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SPACE PHYSIOLOGY
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Weightlessness in space
• A person in an orbiting satellite or a non-propelled space craft experiences weightlessness or a state of near zero gravity force ---microgravity.
• Simply float inside the chamber.
• Reason::gravity act on both space craft and person the same time so both are pulled exactly with same force and in same direction.
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Challenges of weightlessness
• Motion sickness for first few days---because ofunfamiliar motion signals to brain and due tolack of gravitational signals.
• Translocation of fluids within the bodybecause failure of gravity to cause normalhydrostatic pressures.
• Decrease physical activity as no strength isrequired to work against gravity.
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Cont;
• Decrease bone mass.
• Cardiac and skeletal muscle atrophy.
• Decrease work capacity, blood volume, Reduced orthostatic tolerance, Impaired baroreceptor reflex(cardiovascular deconditioning).
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How these effects can be prevented??
• Regular exercise.
• Application of intermittent artificial gravity.
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• Why P02 is low at high altitude
• Acclimatization
• Compare and contrast acute and chronicmountain sickness.
• Effect of positive and negative gravitationalforce on body.
• Reason and challenges of weightlessness inspace and how it can be prevented.
Important one:::
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