Effects on the Organism during Compression
Scuba Diving Medicine is
usually considered complicated not only to learners but also to instructors.
The separate issues and events are interconnected. This section provides
a thorough outline that reviews the main points in the medicine of scuba
Speed of Descent
The speed with which the
scuba diver can safely descend depends on his quickness of equalizing the
pressure in the head cavities, and his training. It is more difficult to
equalize in the first ten meters that at a depth of 100 meters. For example,
diving from 100 m to 110 m is like diving from the surface to 1 m. After
careful equalization in the first ten meters, the diver can reach 30-40
meters for one minute. Of course, this speed rests with the individual’
s ability and his healthy condition.
Depth of Diving
The scuba diver breathes
air under pressure from the aqualung. That is why the permitted depth of
diving depends on the type of the breathing apparatus and the gas with
which it is filled. Improper use or lack of knowledge lead to problems.
- diving with pure oxygen
In hyperbaric conditions
(conditions of increased pressure), oxygen changes its effect on the organism.
From a gas of vital necessity at normal pressure, it turns into a toxic
gas below a particular depth (13 m if breathing pure oxygen – 100% purity,
and 105 m if breathing air) and stay of 20 minutes. In such case, there
occurs oxygen toxicity which develops rapidly. It is assumed that hyperbaric
oxygen destroys some key processes in the nerve cells. This results in
overexcitation in the central nervous system leading to convulsions and
death. Because pure oxygen is toxic below 13 m, it is obligatory that the
percentage of oxygen in deeper dives be decreased. For example, the breathing
mixture of dives below 80 meters consists of 90/95 % helium and 10/5 %
oxygen respectively. The small percentage of oxygen is compensated by its
raised partial pressure which normally ranges from 120 mm Hg to 350 mm
WITH PURE OXYGEN
Lack of oxygen; the partial
pressure of oxygen falls below 120 mm Hg
|Improper handling of pure-oxygen
apparatus; If oxygen is not 100 % pure because of a mistake, nitrogen will
remain after the consumption of O2. The diver cannot realize the difference
and loses consciousness.
||Good mood, jauntiness without
Later – dizziness, suffocation,
|The patient should be given
pure oxygen to breathe; artificial respiration, outer irritation (slaps,
amonia under the nose)
partial pressure of oxygen
exceeds 360 mm Hg
|7 m – the process of receiving
O2 and releasing CO2 is hindered;
13 m – this process stops
so that cells cannot accept oxygen despite of its abundance;
|at first – discomfort, nausea,
spasms of lips and eyelids, disturbances in eyesight, sleepiness;
later – stiffness of muscles,
convulsions (similar to the epileptic ones), blackout, death
|The diver should be taken
out to breathe fresh air.
CO2 toxicity - the partial
pressure of CO2 is higher than normal;
|Improper use of pure-oxygen-apparatus;
not working absorber
||Rapid pulse rate, shortness
of breath and rapid heart beat, rapid respiration, headache, blackout
Access to fresh air;
WITH COMPRESSED AIR
Disturbances which occur
diving with compressed air at a depth of over 4 at
|It is assumed that at increased
pressure, N connects with body’s fats, thus destroying the normal
physiological functions of the cell and leading to disturbances in the
central nervous system. Factors – stress, heavy work and CO2 retention
||First phase – “alcoholic
intoxication”, euphoria – jauntiness and high spirits
Second phase – fatigue,
sleepiness, loss of consciousness and drowning
|Go back several meters and
there will be nothing left of this disease.
It is not a common disease
because carbon monoxide is not found in the atmosphere.
|Carelessness and lack of
knowledge during the compression of air in bottles.
||Headache, noise in the ears,
Later – shortness of breath,
loss of consciousness, death
|Access to fresh air; artificial
WITH GAS MIXTURES
High pressure nervous syndrome;
|This is due to overexcitement
of the central nervous system caused by the increased water pressure. It
occurs at depths exceeding 350 meters.
||Dizziness, nausea, tremors,
loss of dexterity and memory
||Prevention is the best treatment.
Stage compression with long
Add N to the breathing mixture
to become trimix (He, O2, N)
7 – safe depth
for diving with pure oxygen
13 – the limit of
diving with pure oxygen
40 – danger of nitrogen
60 – the limit of
diving with compressed air; diving can continue with a cocktail
350 – danger of HPNS
Effects on the Organism during Decompression
Decompression of Dissolved Gases
Air consists of nitrogen
and oxygen. One part of oxygen is consumed and another is replaced by carbon
dioxide. That is why the gas that concerns diving and decompression most
Nitrogen is an inert gas
in the organism. It does not take part in the exchange of substances and
respiratory processes. There is about 1 liter of nitrogen which is dissolved
in fluids and cells. During compression, nitrogen is intensively absorbed
by the blood and dissolved in the organism until the partial pressure inside
and the ambient pressure are equalized (saturation). During decompression,
the reverse process takes place. Because of the decrease in water pressure
with ascent, the partial pressure of nitrogen in the organism becomes higher
and the gas is released by the cells and tissues (desaturation). This principle
concerns helium, hydrogen and other inert gases too.
The speed of desaturation
is a major problem in diving medicine.
If the diver ascends too
fast and before complete desaturation, nitrogen begins to form bubbles
in the organism. These bubbles are very dangerous because they can plug
small arteries and cause serious damage by stopping the blood flow to a
|The formation of gas bubbles
in the organism during ascent is called decompression sickness, known also
as “the bends”.
They occur 5 minutes to
1 hour after the ascent, sometimes after 2-4 hours. Symptoms range cough,
itching, reddened skin or pains in the joints to serious respiratory, cardiac
and mental damage (such as rapid pulse and heart beat, shortness of breath,
pains in the chest and stomach, paralysis of limbs)
The only remedy to do away
with decompression sickness is the chamber for recompression. The diver
is exposed to the same pressure (at which he was before the beginning of
bubbles’ formation), necessary to dissolve the bubbles. Afterwards, the
pressure decreases on stages to avoid decompression sickness.
Energetic movements, vigorous
massages and hot baths (38 C) are recommended to the patient.
1. Follow the rules for
a safe stay under water which you can find in decompression tables. The
latter are very helpful – they provide safe ascent (free from decompression
sickness) from different depths with different duration and breathing mixtures.
2. In case of failure or
accident, when during ascent there is a danger of “the bends”, the disease
can be avoided if the diver returns to the same pressure in the next 5
min (habitat, chamber, bell).
Time for decompression –
the time needed for the regular release of nitrogen from the cells and
tissues. It is estimated according to decompression tables. For example,
a diver, staying at a depth of 180 m for several minutes has to make 12-hour-decompression.
There are three basic types
How to determine how long and
at what depth to stay under water without making any decompression stops?
Stage decompression Divers,
who have stayed for some time at a particular depth, start ascending. The
ascent is not right on to the surface but it is interrupted by several
stops. Each upper stop should not exceed half the pressure of the previous
Decompression with changing
the inert gases in the breathing mixtures example: from helium-oxygen
These are the most frequent dives because they are performed at shallow
depths where no time for decompression is needed.
X + Y less than 50
X – depth (meters), Y –
Examples: 15 meters – up
to 35 minutes (15+35=50), 20 meters – 30 minutes, 35 meters – 15 minutes.
This concerns measures in meters and minutes only!
Remember: Up to 13 meters
of depth, no-decompression dives are unrestricted in terms of time.
Decompression of Gases in Body Cavities
During ascent, always exhale and do not hold your breath! This rule should
be strictly observed. Otherwise, the most fearful and dramatic disease
occurs – barotrauma of the lungs which often ends in death.
of the Lungs
During ascent, the ambient
pressure decreases. If the diver holds his breath, the air in the lungs
expands and the pressure in the organism becomes greater than that of the
outside. If the difference is too large, the expanding air causes a rupture
of the lungs’ tissue.
Do not hold your breath
What happens in the organism?
- air embolism
The damage of the lung’s
wall lets air bubbles out, right in the blood. The air bubbles are distributed
in the whole body, thus blocking blood vessels in important organs (such
as the heart and brain).
- Because of the lungs’
rupture, air enters the space between lungs and chest so that the former
cannot perform respiratory movements any more.
- Interstitial emphysema
Air, escaping form the lungs,
passes upwards to some interstices. It might get under the neck and shoulders.
strong pain in the chest,
with cough, blood spume from the mouth and nose, shortness of breath, fatigue,
paralysis of limbs, loss of consciousness.
- arrange transfer to a
chamber for recompression or the nearest medical center
- lay the diver down on
his left side, with his head in a low position (to stop bubbles from entering
the brain and heart)
- do not transport the diver
with a plane
- provide the patient with
pure oxygen and medicines
The Psychological Aspect of Scuba
Human stay under water is
connected with a lot of positive emotions and strong impressions. The mysterious
underwater world, so different from ours, hides pleasant surprises and
unsuspected discoveries. It is a place where man feels free of gravitation
and has freedom of movement.
psychic state of a person under water depends on the “collision” of his
motivation and the influence of water. If a person is highly-motivated
and adaptive to the surroundings, his psychic state is excellent. If the
person has no motivation, which cannot overcome the influence of water,
his psychic condition is not stable – often such dives finish with failure.
The most dangerous psychic
condition is the state of panic. Research shows that most cases of death
under water are due to panic. Why is panic so dangerous?
Serious psychological problems
occur in saturation dives where 2-6 divers are isolated from our world
and live underwater for periods of up to 1-2 months. The following changes
are observed – reduced working capacity, mental derangement and lack of
Panic-stricken person starts
breathing intensively (hyperventilation). This leads to dizziness and even
Another possible reaction resulting
from panic is “cessation of breath”. It is due to a spasm in the vocal
cords which block the passage of air to the lungs. Quick, panic ascent
may add up to barotrauma of the lungs.
The feeling of being out of
breath may raise a panic and cause disorders in respiratory and cardiac