AVIATION, HIGH-ALTITUDE, AND SPACE PHYSIOLOGY

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AVIATION, HIGH-
ALTITUDE, AND SPACE
PHYSIOLOGY
Prof. Milan Taradi, MD, PhD
Department of Physiology and Immunology
Medical Faculty, Zagreb

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PROBLEMS IN AVIATION AND
SPACE PHYSIOLOGY
1. EFFECTS OF LOW OXYGEN PRESSURE
ON THE BODY (Hypoxia)
2. EFFECTS OF COLD TEMPERATURE AND
RADIATION IN AVIATION
3. EFFECTS OF ACCELERATORY FORCES
ON THE BODY IN AVIATION AND SPACE
PHYSIOLOGY
4. EFFECTS OF WEIGHTLESSNESS IN
SPACE

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HYPOXIA
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 Hypoxia is a deficiency of oxygen at the tissue
level.
 Classifications:
 1. Hypoxic hypoxia - caused by a low pO2 in
arterial blood.
 2. Anemic hypoxia - too little functioning
hemoglobin in the blood.
 3. Stagnant (ischemic) hypoxia - results from
the inability of blood to carry oxygen to tissue
fast enough to sustain their needs
 4. Histotoxic hypoxia - the blood delivers
adequate oxygen to tissues, but the tissue are
unable to use it properly because of action of a
toxic agent.

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EFFECT OF THE LOW OXYGEN
PRESSURE
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 The total pressure of all the gases
in the air, the barometric
pressure, decreases as one rises
to higher and higher altitudes.
At low altitudes the alveolar
PO2 does not decrease quite so
much as the atmospheric PO2
because of increased
pulmonary ventilations.
At high altitudes PO2 decreases
more than the atmospheric
PO2, because of constant
portions of water vapor and
carbon dioxide.

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THE “CEILING” IN AN
UNPRESSURIZED AIRPLANE
When breathing air, the
ceiling for an aviator is
approximately 7 km
(23,000 feet; saturation of
hemoglobin is
approximately 0.5).
When breathing pure
oxygen, the ceiling is
approximately 14 km
(47,000 feet).
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ACUTE EFFECT OF HYPOXIA
Labored breathing (dyspnea) and
hyperventilation (2,5 km to 6 km)
Lack of concentration
Lack of muscle control
Inability to perform delicate or skill-requiring
tasks
Drowsiness
Weakness
Headache (3,5 km)
Agitation and euphoria
Loss of consciousness
Death (7 km)
oxymeter
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ACUTE ACCOMMODATION TO
LOW PO2
Increased pulmonary ventilation
(immediately to a maximum of
about 65%, and for several days
500 to 700%)
Increased diffusion capacity
(200%)
Increased cardiac output (30% but
usually it falls back to normal
within a few days)
The biphosphoglycerate (BPG)
concentration increases
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CHRONIC ACCLIMATIZATION TO
LOW PO2
Increased hemoglobin in the blood
(to 220 g/L)
Increase of hematocrite (to 0.65)
Increased blood volume (30%)
Increased vascularity of the tissue
“Naturally acclimatized” persons
because of genetic differences
Increased ability of the cells to
utilize oxygen
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ACUTE MOUNTAIN SICKNESS
Only a small percentage of peaple who
ascend rapidly become acutely sick.
Clinical features:
Acute cerebral edema
result from local vasodilatation, caused by the
hypoxia.
Acute pulmonary edema
the cause of this is extreme pulmonary
vasoconstriction caused by the hypoxia.
The therapy is breathing of oxygen or
moving to a lower altitude.
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CHRONIC MOUNTAIN SICNESS
The some person who remains at hight altitude
too long develop occasionally chronic mountain
sicness (Monge´s disease).
The following effect occur:
red cell mass become extremly high (polycythemia)
blood viscosity increases
pulmonary arterial pressure becomes elevated
pulmonary vasoconstriction
enlargement of the right heart
decrease of periferal arterial pressure
congestive heart failure
death.
The person must be moved to a lower altitude
to prevent fatal pulmonary edema.
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EFFECTS OF COLD TEMPERATURE
AND RADIATION IN AVIATION
The cold temperature of the upper
atmosphere involves the same
physiological problems as cold
temperatures on the surface.
The electromagnetic radiations
from the Sun (ultraviolet) at high
altitudes involve the same
problems as on the surface.
In space physiology there is
significant hazard from gamma and
x-rays.
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EFFECTS OF ACCELERATORY
FORCES
The force of impact can cause death by
rupturing or breaking different structures of
the body.
Deceleration - The force of impact is
proportional to the kinetic energy divided by
the distant of stopping.
The most important effect of acceleration is on
the circulatory system, because blood is
mobile.
Types of acceleratory forces:
positive G (toward the lowermost part of the body)
negative G (toward the head)
transverse G (transverse to the axis of the body).
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EFFECT OF ACCELERATORY FORCES
ON THE BODY
Positive G
blood is centrifuged toward feets
decrease of cardiac output and arterial pressure
"black-out" of vision
nunconsciousness (4 to 6 G within few seconds).
Negative G
hyperemia of the head
"red-out" hyperemia in the eyes
increase of arterial pressure
stop of heart beating
rupture of small vessels in the head and in the brain.
Transversal G (lying)
pulmonary colaps
vertebral fracture (hgreater than 20 g)
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EFFECTS OF WEIGHTLESSNESS IN
SPACE
The effects of prolongated stay in
space are not severe, and are the
same as in people who lie in bed
for an extended period of time.
decrease in blood volume
decrease in muscle strenght
loss of calcium from the bones
The extensive exercise programs
are carried out by astronauts.
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ADAPTATION IN SPACE
 Adaptation of neurovestibular system, fluids and
electrolytes, cardiovascular system, and red blood cell
mass.
 The line of demineralization and radiation effect
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CONCLUSIONS
HYPOXYA AND COLDNESS ARE
THE MAJOR PROBLEMS AT HIGH
ALTITUDE AND
ACCELERATORY FORCES IN
AVIATION AND SPACE
PHYSIOLOGY.