Here you
will find a description of:
THE DIVING
RESPONSE/REFLEX
Human life begins in an
aqueous environment and the first 9 months as embryos in
mothers womb we do not breathe with our lungs. All oxygen
(O2), which keeps us alive, flows to us through the
umbilical cord and originates from our mothers blood in which
oxygen is bound to specific transporter proteins called the
red blood cells or erythrocytes. When we are born and the
umbilical cord is cut it is the start of a whole new era,
mainly because we now have to breath ourselves. After coughing
water from our lungs we take our first breath. We are now an
independent organism which can supply the vital oxygen to
every cell in our body. Apart from the oxygen bound to the red
blood cells and apart from the oxygen we have in our lungs, we
also have a an oxygen reserve in the muscles called myoglobin.
In aquatic mammals such as seals and whales, which often have
to make prolonged and deep dives in order to feed, very high
concentrations of myoglobin and erythrocytes are found which,
among other things, makes it possible for these animals to
remain submerged almost one hour. In addition these creatures
exhibit a diving response - (The mammalian diving
response/reflex), which has also been preserved in terrestrial
mammals - human beings inclusive. The diving response is
provoked when the body and especially the face comes under or
in contact with water and is amplified when the body goes
deeper and deeper into the water. The diving response includes
a number of mechanisms which all contribute to prolong the
time by which the body can cope without extra oxygen. In other
words the diving response helps economizes with the amount of
oxygen given. The primary mechanisms are constriction of the
peripheral cardiovascular system and a lowering of the heart
frequency called bradycardia. Constriction of blood vessels in
the extremities ensures that blood is concentrated where it is
most necessary - namely in the 'small' circuit between the
lungs, the heart and the brain which is the most oxygen
sensitive organ of our body. The reduction in heart beats per
minute also contribute to oxygen conservation since the heart
muscle does not need much oxygen at a lower working intensity.
The diving response is regulated by various receptors in the
living organism. Some of these receptors are subordinated to
the autonomous nervous system which is the part we can not
control by our will. By repeated diving or by just holding
one's breath the sensitivity of these receptors can be changed
in such a way that the body can remain in apnea
(breath-holding).
Some examples to mention are
an increase in the number of red blood cells which allow for a
higher concentration of oxygen in the blood. In this case one
speaks of high 'hematocritic' values. Another example is a
chance in the sensitivity of the carbon dioxide
(CO2) receptors which are placed in the lower
posterior part of the brain. CO2 is a waist product
which is made from 'used' O2 and water
(H2O) and which, via the lungs, leave the blood
when we breath out. If we are prevented from breathing then
the concentration of CO2 will rise and at some
point reach a level which is so high that the CO2
receptors will signal to the brain that we have to breath out
NOW. By lowering the sensitivity of the CO2
receptors or by adapting psychologically to higher
CO2 concentrations it is actually possible to
prolong the breath-holding time before the brain tells you to
breathe. CO2 rather than O2 is the most
important regulator for breathing. In other words the body is
more sensitive to high CO2 concentrations than to
low O2 concentrations which implies that one will
breathe automatically BEFORE the O2 concentration
drops to dangerous low levels.
SAMBA
When breathing faster or
deeper than normally, termed hyperventilation, large amounts
of CO2 are removed from the blood. This implies
that the signal from the CO2 receptors to the brain
that one has to breathe is postponed. If a person passes below
the critical O2 value muscle-cramps and
unconsciousness will occur. Because muscle-cramps are
involuntary and sometimes rather intense this condition is
referred to as 'samba' within the world of freediving. This is
the sign of the body that its physiological limit has been
exceeded and every incident of this character is penalized
with a disqualification in the specific discipline. (This,
however, depends on the federation. AIDA does not allow sambas
whereas F.R.E.E. does). A samba is not something to joke about
but at the same time it is not something one has to fear with
awe. Should a samba occur, either during training or during a
competition one knows that the limit has been passed. The
trick then is to learn from the episode and to interpret and
analyze the signals which emerged just before the incident in
order to be able to stop just before floating into the
abyss.
The most important thing for
a person with samba is, obviously, that he is given oxygen (or
normal air) immediately. Does this not happen - for instance
if it occurs under the surface then a samba can develop into a
black-out which is a deadly serious state of unconsciousness.
In the worst case heart failure can also occur.
BLACK-OUT
Different types of Black-outs
occur of which shallow water black-out (SWBO) is the most
common in connection with constant weight diving. There are
primarily two reasons for this. First of all the freediver
uses a lot of oxygen on diving down to the maximum depth and
back to the surface. Secondly - and maybe most importantly -
the physical laws are so (Boyles Law concerning gasses and
pressure) that the partial pressure of oxygen i.e. the portion
of air (gas) pressure in the lungs which is made up of oxygen
falls most rapidly just before the diver reaches the surface.
This is due to the fact that a gas pressure of 2 atm/bar exist
on 10 meters of depth whereas it is only half this value (1
atm/bar) on the surface. The volume of the lungs in the
surface is therefore double the value at 10 meters. The
partial pressure of oxygen can thereby be so small that no
oxygen diffuses into the bloodstream which leads to instant
unconsciousness. It is comparable with unplugging the
computer. The enormous danger of SWBO is that the body does
not receive any crystal clear warning signals. As a matter of
fact the low partial pressure which exist in the lungs just
before the freediver reaches the surface can lead to a
diffusion of CO2 from the bloodstream to the lungs
which results in a weakening of the respiratory signal to the
brain. This gives a false feeling of "safety" and of still
having a lot of air.
SAFETY
Every year
freedivers die as a result of SWBO which is most tragic.
However, the direct course of death is not SWBO but drowning.
This is due to the fact that many freedivers offend against
the 1. Law of freedivers and scuba divers alike; 'NEVER DIVE
ALONE'.
As a freediver it is
essential to have a thorough knowledge of the body and its
physiology. Furthermore it is important to know how mental and
physical training can influence on the physiology.
DIVING SICKNESS
(DECOMPRESSION SICKNESS)
Many people erroneously
believe that freediving leads to decompression sickness. The
main difference between the freediver and the scuba diver is
of course that the scuba diver inhales compressed air. This
air is taken in with a pressure which is equal to the pressure
of the surrounding water (depth) which is due to a clever
device in the so-called 1. Step of the scuba equipment. The
problem of decompression sickness does not occur on large
depths. Rather, it occurs when a scuba diver returns from a
large depth and the longer time he has spent there and the
faster he returns - for example in case of an
emergency/accident, the bigger the risk. Because the scuba
diver is breathing normal air consisting of 78% nitrogen
(N2) this will, just like O2 and
CO2, diffuse into the blood and be in equilibrium
with the gas pressure at the given depth. If a scuba diver has
remained for a longer period of time at some depth and thereby
accumulated N2 gas in the blood this will not be
able to leave the blood if he ascends too fast. The effect is
exactly the same as opening a soda water in one go - a lot of
bubbles will be created because of the rapid change in
pressure prevent the liquid to get rid of its gasses. These
N2 bubbles will first get stuck in the joints, such
as elbows and knees. This is the reason why decompression
sickness is often referred to as 'the bends'. If the bubbles
get stuck in the heart or in the brain it may have fatal
consequences.
The treatment of
decompression sickness is related to pressure. Either the
scuba diver dives bach to a depth where the bubbles are
dissolved or, if possible, he is brought to a decompression
chamber. In this chamber the pressure will be lowered
gradually which is the equivalent of opening the soda water
slowly. Inhalation of pure oxygen can also help to rinse
N2 out of the blood stream more quickly.
To be correct it should be
mentioned that paralysis in legs, arms or one side of the body
has been observed in pearl divers, spear fishermen and in a
few freedivers who have been diving to extreme depths and
having returned very quickly. By doing repeated dives
N2
will accumulate in the bloodstream. The longer the
freediver stays at a large depth and the more dives he makes
the larger the risk of freediver 'decompression sickness'.
This is why pearl fishers and competitive spear fishermen are
sometimes hit by this condition. The phenomenon was first
described by the Danish physiologist Poul-Erik Paulev who
carried out experiments on his own body in order to collect
data for his Doctor degree which I have listed below. Today it
is known that if a freediver/spear fisher man triples the time
at the surface, compared to the time submerged, the negative
effects of N2 accumulation can be avoided.
Therefore, obviously, this is a good rule of thumb when
freediving.
Knowledge on the aspects of
paralysis as the course of extreme deep freediving is still no
existing but it is known that a slow ascent can reduce the
risk. This is why the best 'deep' freedivers in the world,
such as Löic Leferme and Umberto Pelizzari let go of the air
balloon at a depth of 30 - 45 meters and swim or pull
themselves back to the surface when they perform record
attempts to impressive 150 meters in the 'No Limit'
category.
EQUALIZATION
The true
factor which often prevent many freedivers from reaching new
depths, apart from the psychological one, is most often
lacking technique and air to equalize the ears with. In
contrast to scuba divers which have hundreds of liters of air
available the freediver brings only the air which he takes
into his lungs just before diving. Already at a depth of 10
meters the volume of the lungs is reduced to one half and at
30 - 40 meters the volume of air will be so small that
equalization with normal Valsalva or Frenzel maneuvers is
impossible. If a freediver wants to go deeper more
sophisticated techniques are necessary. One such technique is
diaphragmatic Frenzel, by which the freediver lifts his
diaphragm up so high between the ribs that the air from the
'dead space' of the lungs can be utilized to equalization. If
one wishes to dive even deeper then the Frenzel-Fattah
maneuver is the answer. Briefly explained the trick of this
maneuver is to fill the mouth with air and close the trachea
approximately 15 meters before the depth is reached where
equalization with diaphragmatic Frenzel is not longer
possible. Doing this it should be possible to equalize 3 - 5
more times. The Frenzel-Fattah and other
equalization-techniques
are explained thoroughly and very
educationally by my Canadian friend and former world record
holder in constant weight (82 meters), Eric Fattah.
EPILOG
It is the pleasure, the
marveling, the astonishment and the curiosity of discovering
more and more layers of oneself which drive every
freediver.
If you are a happy 'amateur'
- a true little fish who loves to splash around in the wet
element and for example do snorkeling whenever there is a
chance then just a little bit of physical and mental 'mind'
training will make it possible for you to be able to bring the
sensation of joy and tranquility up on land. As this sensation
will make you relax and lower your heart beat it is often
convenient in a tense or stressed situation.
If freediving on a higher and
maybe more serious level it is possible, through hard physical
training and through meditation and concentration exercises,
to move into zones where only few 'normal' people have
been. This is
both in respect to the extreme pressure conditions which exist
in deep deep down the ocean but also the very low heart
frequencies which are experienced after longer periods of
breath-holding.
The common denominator for
these experiences is that they give rise to emotions of
'happiness' and a feeling of inner peace which is difficult to
express in words and together they create a rapture which
liberates one from both time, body and soul. The skeptic
reader might postulate that this sensation of joy is due to
severe narcosis, which is a form of oxygen poisoning that can
occur at great depths or that the brain is lacking oxygen
whereby the freediver soars into never never land. This is
not, however, always so since the same happiness can manifest
itself in very shallow water and with the lungs full of fresh
air. Whatever the case it is these sensations and feelings
which permit the freediver to get into contact with still new
and unknown aspects of himself and give access to unconscious
emotions which possibly have roots back to the first months of
our babyhood - or possibly even further back!
LITERATURE
If you want to know more
about the many interesting mechanisms which regulate and
control animals and humans under different physiological and
environmental conditions you can learn more from these books
and articles:
Ferretti, G. 2001. Extreme human breath-hold
diving. European
Journal of Applied Physiology - 84: 254-271
This article deals with the
respiratory, circulatory and metabolic adaptations which occur
in humans during extreme freediving. If you do not have
'special' knowledge within the fields of medicine or biology
it might seem a bit tuff to read but certainly not impossible
to understand.
Schmidt
- Nielsen, K. 1997. Animal Physiology -
adaptation and environment. Fifth edition. Cambridge
University Press,
1997.
In this splendid textbook the
main problems which humans and animals face when diving are
explained in chapter 5. Further than just touching upon the
mechanisms which constitute the diving response topics such as
narcosis and decompression sickness are also described.
Randall,
D. et al. 1997. Animal physiology -
mechanisms and adaptations, fourth edition. W.H Freeman
and Company. New York. (especially chapters 12 & 13)
This textbook gives a
comprehensive view on the cardio-vascular system and on
elementary aspects of gasses (O2, CO2,
N2 etc.).
Butler,
P. J., & Jones, D. R. 1997. Physiological Reviews
- physiology of diving
of birds and mammals. Volume 77,
number 3. Page 837-899. July 1997.
This review article collects
data from more than 400 articles and give a thorough and
in-depth description of the physiological diving response in
birds and mammals.
Schagaty, E. 1996. The human diving response
- effects of temperature and training. University of Lund,
1996.
This book, which is actually
Schagaty´s Doctor thesis, describes the human diving response
as results from experiments with groups of 'normal'
persons.
Paulev, P. E. 1965. Decompression sickness
following repeated breath-hold dives. Journal of Applied Physiology - 20: 1028-1031.
Paulev, P. E. 1965. Respiratory and
cardiovascular effects of breath-holding. I Acta Physiologica Scandinavica - suppl. 324, 1969.
Paulev describes in words and
numbers the earlier mentioned freediver 'decompression
sickness' from his own experiments.
