The human organism consists
of various systems and organs that have common functions. At diving, the
human organism is placed in a new breathing media where all these systems
and organs are affected. This section contains a short description of man’s
physiology and explanations of water pressure on it. |
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The Circulatory System
In the circulatory system,
blood is transferred via arteries, capillaries and veins to and from the
heart.
 The
heart is divided into four parts – right and left auricles and right and
left ventricles. The right side of the heart (in blue color, the picture
is a mirror reflection) pumps blood, poor in oxygen, through the veins
to the lungs for new oxygen. The left side receives blood, rich in oxygen,
from the lungs and transfers it through the arteries (in red) to the rest
of the body.
Because of the irregular
allocation of pressure on the body under water, blood circulation has its
peculiarities. If water pressure is higher at the legs of the diver,
squeezing of blood vessels in the lower limbs occurs. On one hand, blood
is more easily transferred to the head (where the pressure is considerably
lower) and plethora (blood flow) occurs. On the other hand, blood is delivered
with difficulty to the legs which are under greater pressure and drain
of blood (lack of blood flow) occurs. Such distribution of blood loads
more the heart and deteriorates the normal circulation of blood. As a result,
overcooling of the lower limbs may take place. If the difference of pressure
between the upper and lower limbs is insignificant, such is the load of
the heart.
The Respiratory System
 The
function of the respiratory system is the interchange of gases, oxygen
and carbon dioxide with the atmosphere. Air is inhaled through the nose
or mouth and it is delivered to the lungs by the pharynx, larynx, trachea
and bronchi. Exhaled air returns through the same path.
The amount of air which lungs
can hold depends on the person’s condition, training and pulmonary state.
At rest, lungs can naturally contain about 2.5 liters of air. This volume
of air is called “breathing volume” . After our regular inhalation, we
can willingly take in “additional volume” of air. On the reverse, at the
end of our regular exhalation, if we try, we can still breathe out – and
this volume is referred to as “reserve volume” of air. Approximately 1200cm3
of air always remains in the lungs and cannot be exhaled unless the chest
is squeezed with force.
 The
sum of the breathing, additional and reserve volumes defines vital capacity
which depends on the size, age and physical state of the person. Vital
capacity + residual air makes up the total pulmonary volume.
Lungs are located in the
thorax. During inhalation, the ribs move up and out and the diaphragm goes
down. Thus, the volume of the thorax is increased allowing air to enter
the lungs. During exhalation, the ribs move downwards and inwards and the
diaphragm rises. This way, the chest contracts and forces the air from
the lungs.
A common problem with respiration
for the free diver and the scuba diver is tiredness of respiratory muscles,
cause by differences in pressure under water. Breath-hold divers have to
overcome the air resistance in the snorkel and divers with autonomous diving
suits have to cope with the resistance in breathing apparatuses.
 The
Digestive System
Mechanism of digestion
The process is divided into
three phases – function of the teeth (chewing the food to small particles),
action of the stomach and intestinal action.
Raised water pressure influences
largely the process of digestion. The work of muscles and the emotional
stress of the diver under water interfere with the regular function of
the peptic glands. There occur changes in taste and preferences to food
(see Smell and Taste).
The Nervous System
The nervous system deals
with reception of irritations, transmission of nerve impulses and stimulation
of muscle mechanism. The nervous system of the diver is exposed to raised
psychological and physiological pressure, and stress. Every dive hides
risk which is accompanied by nervousness and tension on the part of the
diver. That is why divers should be emotionally resistant – there should
be no bustling and confusion. Tenseless, restful daily and work routine
are of essence to the diver. Underwater peculiarities load diver’s nervous
system with increased amount of carbon dioxide, lower amount of oxygen
and increased partial pressure of oxygen and nitrogen. Data show that highly-qualified
divers are extremely resistant to physical pressure of all kinds.
The Excretory System: Sweat Glands
Neoprene suits decrease
perspiration under water. However, a diver placed in a chamber for recompression
sweats a lot.
Cavities of the Body
The Ears
 The
ears are organs of hearing and equilibrium. Both functions might be disturbed
under water because of the inability of the diver to equalize the pressure.
The ear is divided into external, middle and internal parts. The external
ear includes the auricle (the outer flap of the ear) and the external auditory
canal which leads to the eardrum (or tympanic membrane). The middle ear
is located on the inner part of the eardrum and is connected to the back
of the nose and throat (nasopharynx) by the eustachian tube. It contains
three bones – the hammer handle, the anvil and the stapes. The internal
ear, or labyrinth, is composed of the cochlea (“snail shell”), the vestibule
and three canals.
Physiology and Hydrostatic
Pressure
1-2 m no earaches
3 m
a feeling of weight in the ears
4 m
pain
6-7 m
the pain spreads out to the jaws, face and the whole head
8-9 m
strong and unbearable pain which persuades the person to ascend if he does
not know how to equalize
Under water, divers often
experience pain in their ears. This is due to the raised water pressure
which causes the eardrum to bend. In order to equalize the pressure out
of and in the middle ear, it is necessary that air enter from the mouth
through the eustachian tube to the middle air. The valve of the eustachian
tube is usually closed and it can be opened only through contractions of
the nasopharyngeal muscles.
This can be done through
swallowing, yawning, gently blowing with closed nostrils, moving the tongue
and other ways. You may also wish to visit the Training
Section. These methods should start from the surface and be repeated
every 1-2 meters. If the pressure cannot be equalized at once, divers should
go up 1-2 meters and try again.
Diseases
Barotrauma
| The large difference between
the ambient pressure and that of the body’s air-containing cavities may
cause injury by damaging the involved tissues. This injury is called barotrauma. |
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Barotitis
Media
This is inflammation of
the middle ear due to insufficient pressure equalization. Another name
for barotitis media that is more popular among divers is middle ear squeeze.
If this infection does not worsen, the diver will feel much better in a
week.
Symptoms and Treatment
Barotitis media is characterized
by earaches, a feeling of fullness and reddened eardrum. It is cured with
warm applications to the ear and antiseptic medicines. |
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Middle
Ear Squeeze or “Ear-Deafening”?
The feeling of “deafened”
ears disappears after drying them (picture a).
Picture c shows how middle
ear squeeze affects the ear – plugged eustachian tube, damaged inner ear’s
mucous membrane. |
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Eardrum
Rupture, Labyrinth Crisis
If the diver does not equalize
the pressure but ignores the pain and continues to dive deeper, raised
pressure exceeds the strength of the eardrum membrane and tears it. As
a result, water enters the middle ear and cools the surrounding tissues
and the inner ear. Most affected are the cells of the vestibular system
which start transmitting chaotic information for 1-2 minutes. The diver
loses orientation, he is dizzy and nauseous. This state is known as labyrinth
crisis.
Prevention
In a case of labyrinth crisis
and disorientation, it is recommended to let some air bubbles and follow
them to the surface.
Avoid wearing ear-stoppers
if you do not know how to use them. Otherwise, instead of isolating the
external ear from contact with water, ear-stoppers might even cause eardrum
rupture because of the impossibility to equalize. |
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Inner-Ear
Decompression Sickness
| It occurs as a result of
rapid decompression. In the fluid of the inner ear (or labyrinth) are formed
nitrogen bubbles which irritate the vestibular system and cause inner-ear
decompression sickness. Its symptoms are similar to those of the labyrinth
crisis. |
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The Sinuses
Sinuses are air-filled cavities
located in the head and cheekbones. These cavities are connected to the
nasal cavity by means of large openings through which aid can pass with
no difficulty. Problems occur with divers suffering from sinusitis or cold.
In these cases, the openings become so narrow that air cannot pass freely.
As a result, strong pains are felt in the sinuses because of the impossibility
of air to either enter of leave and of pressure to be equalized.
The Mouth Cavity
 Under
water, pains might be felt in cavities in a rotten tooth or under fillings
and crowns. During ascent, air that has entered any hollow places in the
tooth cannot come out because of pressure. This leads to breaking the tooth
or removing fillings or crowns. |
