Research article
Volume 4, No. 1, 2012, 53-61
UDC 797.215-051:612.22
Ognjen Pedja Tutorov
Center for Education and Research of Free Diving ìDolhpinboyî
Zrenjanin, Serbia
In static apnea discipline diver holds the breath in standstill condition. Diving
reflex represents a reaction of the body to apnea dive with responses of effectors:
bradycardia, peripheral vasoconstriction, splenic contractions. Physiological significance
of these body changes implies reduction of oxygen consumption. The main objective of
this research is to examine characteristics of connection between heart rate changes (HR)
and changes in oxygen saturation in blood (SaO2) during apnea. A group of 15 breath
hold divers was examined. Tests were conducted during static apnea, heart rate (HR) was
measured as well as oxygen saturation in blood (SaO2). The changes in HR and SaO2
during apnea demonstrated statistically significant correlation. Higher HR values in apnea
indicate higher mental tonus during apnea which is followed by higher muscle tonus. The
consequence is a greater consumption of O2 and lower values of SaO2min. There is
statistically significant correlation between intensity of diving reflex activation and
oxygen conserving (less reduction of SaO2).
Keywords: breath hold diving (freediving), diving reflex, apnea
Breath hold diving (freediving) is a type of diving, i.e. immersion of the body in
the water in apnea condition (holding the breath). It is a sport activity in which the
sportsman (diver), diving with only one breath, reaches certain results regarding the
length, depth or time of the dive. Freediving is natural (physiological) diving, in contrast
to SCUBA (self contained breathing apparatus) and therefore it represents much older type
of diving. In freediving, a diver dives within the physiological limits of the body, using
only his/her own ways of adaptation.
Corresponding author. Center for Education and Research of Free Diving ìDolhpinboyî, Brigadira Risti„a
L 13/19, 23000 Zrenjanin, Serbia, e-mail: dolphin7boy@yahoo.com
© 2012 Faculty of Sport and Physical Education, University of Novi Sad, Serbia
O. P. Tutorov
The most natural type of diving is repeated dives in short apnea. These are repeated
dives within 50-80% of maximum apnea. On the other hand, competitive diving means
performing one sub maximum apnea up to 99% of the possibilities, where the limit is
represented by tolerance to hypoxemia. The main problem of freediving is hypoxemia
(oxygen deprivation while holding the breath). Using various training programmes and
combining different training stimuli, one can stimulate different physiological potentials
and adaptation mechanisms. Training has a positive effect on higher tolerance to oxygen
consumption, tolerance to higher values of CO2, relaxation of body and mind, increase of
breath capacity and quality. Freediving disciplines are static and dynamic apnea, as well as
constant weight.
STA (Static Apnea) represents holding breath at a standstill. Divers float on the
surface of a pool in the state of complete body and mind relaxation. The time which divers
spend holding the breath is measured. The diver wears a diving suit, masks or goggles and
noseclip, and possibly gloves and socks. From the mental point of view, this is the most
challenging discipline in freediving since the diver is in complete standstill condition on
his own. In this discipline the relaxation techniques and mental training are of crucial
Freediving, i.e. apnea represents a combination of factors which have effects on the
1) respiratory arrest
(holding the breath)
2) O2 consumption and building up of CO2 in the body
3) impact of ambient pressure on the diverís body
Current world record in static apnea (STA) 11 min, 35 sec. (AIDA International
23.02.2011 www.aida-international.org).
Physiological changes in freediving. Apnea means respiratory rest ñ absence of
respiratory activity, i.e. air exchange with the surroundings. As a consequence of
metabolic processes in organism, O2 consumption occurs during apnea, i.e. oxygen
saturation in blood and tissue decrease (SaO2), and CO2 build up also starts to occur.
Reduction of O2 consumption means reduced taking O2 from the lungs, as well as slow
O2 consumption in tissues (Lindholm, 1999). Although respiratory activities stop in
apnea, the respiratory process at alveolar membrane, capillary and cell level (all three
breathing phases) is still going on continuously. There are two phases of Apnea:
fist phase (easy going phase) ñ before air urge (diaphragm contraction), high
PaO2, low PaCO2, mostly aerobic phase
second phase (struggle phase) ñ begins with the diaphragm contractions, the
beginning of this phase is determined by high PaCO2, at the end of this phase
there is low PaO2 up to the blackout limit, mostly anaerobic phase.
Changing from the first to the second phase happens at the physiological breaking
point when subjective feeling of urge to breath appears, which is manifested by
involuntary breathing movements, i.e. diaphragm contractions. Physiological breaking
point appears at the moment when PaCO2 reaches values which stimulate respiratory
centres. However, despite the hypercapnia and involuntary respiratory movements, apnea
breaking and breathing can be voluntary postponed (Schagatay, 2001). Training, in other
words repeated apneas, develops tolerance to high values of hypercapnia, as well as higher
tolerance to hypoxemia (Schagatay, 2009). During apnea, the first phase (easy going
phase) takes place within diving aerobic limits. This also applies to short apneas which
are stopped before urge for breath (diaphragm contractions) (Schagatay, 2009). Other
HR and oxygen saturation dependency in static apnea
apneas, which are prolonged after the diaphragm contractions have started, are connected
to accumulation of lactate and appearance of oxygen debt. The second apnea phase is
anaerobic apnea phase.
There are three factors which determine apnea time limits (Schagatay, 2009): a)
organism capacity to store O2, b) tolerance to hypoxemia and/or hypercapnia and c)
minimal oxygen consumption VO2min.
a) Organism capacity to store O2 depends on the size and capacity to store O2:
TLC (total lung capacity), haemoglobin concentration in blood circulation, amount of
myoglobin in muscles and amount of dissolved oxygen in tissues. (Schagatay, 2009).
b) Tolerance to ↓O2/↑CO2. Firstly, the increase of CO2 takes place during apnea,
and then the decrease of O2 begins. Apnea training develops high tolerance to hypercapnia
(↑CŒ2). Beginners break apnea as a result of hypercapnia, whereas more experienced
freedivers break apnea as a result of hypoxemia. Apnea training improves brain tissue
tolerance to low values of O2. Dilatation of brain blood vessels (auto-regulation) and
increase of brain perfusion as a consequence of hypercapnia represent significant
protective mechanisms. In addition to this, significant acidosis as a result of accumulation
of CO2 and lactates appear during apnea. Lactates accumulation occurs in the tissues with
weak perfusion, which is the result of peripheral vasoconstriction as a part of diving reflex
activation. Furthermore, it has been recorded that freedivers have ability to accumulate
double CO2 quantities in their bodies (Schagatay, 2009).
c) Minimal oxygen consumption (VO2min) ñ VO2min represents minimal
oxygen consumption and it is the key physiological factor for determining apnea duration.
VO2min is determined by the following physiological characteristics:
cardiovascular response to the diving reflex
minimal metabolic consumption RMR (resting metabolic rate ñ earlier basal
metabolism BMR)
mental activity CMR (cerebral metabolic rate ñ O2 consumption in brain
skeletal muscles relaxation and LBM (lean body mass ñ O2 consumption in
muscle tissue)
Minimal O2 consumption depends on cardiovascular response to apnea
(bradycardia and bloodshift) and anaerobic metabolism capacity. Caloric intake reduction
lowers RMR for 17%, as well as CO2 production for 30%. Diet which is rich in glucoses
(fats and proteins) has the optimal ratio of O2 consumption
/energy production.
Relaxation reduces O2 consumption for 32% (Schagatay, 2009). VO2min greatly depends
on the diverís psychological state , i.e. current stress level (mental response to apnea).
Relaxation techniques play the key role in freediving training, with three levels of
relaxation: body relaxation, breathing relaxation, mental relaxation. Skeletal musculature
becomes relaxed and brain functions become synchronised (· state of brain waves) in the
state of relaxation. Brain uses 20% of total oxygen consumption, and great deal of the rest
of the consumption is consequence of skeletal musculature activity.
The ventilation process, i.e. outer breathing, does not occur during apnea.
Although the breathing cannot be seen, the process of breathing continues in organism in
three breathing phases (at the alveolar membrane level, blood transport to tissues and
organs and on the cell level). During ìinner breathingî there is a moment when the level of
gases in blood (physiological gases O2, CO2- gases which are included in metabolism)
goes beyond physiological limits. Normal organism function (tissues and cells) takes place
within physiological scope of O2 and CO2 gas concentration. When the limit is reached,
O. P. Tutorov
cell and organism functions become disturbed. O2 consumption and CO2 build up occur
during apnea. The organism struggles to tolerate oxygen reduction, whereas it better
endures increase of CO2. In other words, we are not aware of O2 consumption, but we get
the signal to inhale since CO2 has been built up. The receptors in blood vessels and brain
record CO2 increase and the urge for air rises.
The relationship between partial pressure of O2 in blood and oxygen saturation in
blood is determined by oxyhemoglobin dissociation curve. Oxygen saturation in blood is
determined by partial pressure of O2. The plateau of dissociation curve O2 is safety factor
in hypoxemia. SaO2 is kept above 90% until partial pressure of O2 does not drop below
Diving reflex physiology. Diving reflex represents response of the organism to the
apnea dive, i.e. holding the breath (Lindholm, 1999). Diving reflex is innate, genetically
inscribed model of reactions in organism which is activated when diving (immersion) in
the state of apnea. Identical reflex has been discovered in all diving mammals (dolphins,
whales, seals). The consequences of diving reflex activation are: bradycardia, peripheral
vasoconstriction and splenic contractions. Bradycardia means heart rate reduction,
peripheral vasoconstriction means reduction of blood perfusion through peripheral tissues
which are resistant to hypoxemia. Physiological importance of these changes in organism
means reduction of oxygen consumption (VO2), i.e. storing O2 for the functions of vital
organs (Lindholm, 1999). Splenic contractions inject additional blood and haemoglobin in
blood circulation which increases blood capacity to transport oxygen. Diving reflex, which
represents a series of organism reflex reactions, starts with peripheral vasoconstriction
(result of simpaticus actions), and later vagus bradycardia occurs (result of parasimpaticus
actions). The initial reaction is peripheral vasocnstriction with hypertension, and HR
reduction is, at the beginning, the result of hypertension stimuli to baroreceptors, and later
it is the result of hypoxia stimuli to chemoreceptors (Lindholm, 2009). Repeated apnes
lead to splenic contraction, as a result of simpaticus activation leading to the increase of
haemoglobin concentration in blood circulation (Lindholm, 2009). Past researches showed
that there is a correlation between changes of HR values and SaO2 during apnea
(Lindholm, 1999).
Diving reflex mechanism
Effector organs in apnea: heart, peripheral vascular bed, spleen
The main aim of this research is to examine characteristics of connection between
heart rate changes (HR) and changes in oxygen saturation in blood (SaO2) during
apnea. Also, we examined the connection between the lower heart rate and reduction of
oxygen saturation in blood and apnea duration.
HR and oxygen saturation dependency in static apnea
We used a group of 15 exercising freedivers in our research. The following
characteristics were recorded: height, weight, sex, age, heart rate and oxygen saturation in
blood in standstill condition. All participants were informed about possible risks and they
had made a statement about voluntary participation in this research.
Testing was conducted during apnea in the standstill condition (static apnea) in
water. Prior to testing, each participant spent 10 minutes practicing relaxation techniques.
At the beginning of 8th, 9th and 10th minutes heart rate was recorded in the standstill
condition. During the testing, participants performed one sub maximal apnea (almost 99%
of the maximum). Heart rate values parameter (HR), oxygen saturation in blood (SaO2)
and the time were continuously recorded. The values were recorded every 15 seconds.
During the testing, we stayed in contact with participants all the time since we used the
means of pre-arranged signals of communication.
Heart rate values were measured by pulsometer of polar F11 make, which consists
of a belt which is placed on the chest with electrodes and transmitter. SaO2 values were
measured by digital finger pulse oximeter of Go2 Nonin make, which records changes in
values of oxygen saturation in blood at capillary level (point finger). The time was
measured by stopwatch. Participants wore a noseclip during apnea due to the obstruction
of nostrils, and during the static apnea in the pools they had wet neoprene suits which
covered the whole body except face, hands and feet.
General data regarding participants
The sample specimen we used consisted of 15 freedivers who were active competitors and
who performed their training practice. The study was conducted in controlled conditions,
during the training practice. The divers were in water, they wore wet suits and they
performed static apnea. The study comprised 15 divers, competitors on the national level.
Sex structure was: 13 men and 2 women. This distribution regarding sex is the result of
accidental variation and considering the relatively small number of participants one cannot
make a conclusion regarding sex distribution. Considering age structure, majority of divers
were in their thirties (11 divers). The youngest diver was 19 years old, and the oldest was
49 years old. One diver was in his forties and two divers were in their fifties.
O. P. Tutorov
Characteristics of HR changes in apnea
Distribution of arithmetic means of HR during
Correlation of HRend values and apnea and apnea
duration (STA).
Figure shows distribution of arithmetic means of HR of
There is statistically significant inversive linear
all divers, for each 15 second interval of measuring.
correlation (R= - 0,794 for n-2=11 with 95% 0,55).
Characteristics of changes of SaO2 in apnea
Distribution of arithmetic means of SaO2 during
Correlation of SaO2 values and apnea duration
Figure shows distribution of arithmetic means of SaO2
There is statistically significant inversive linear
of all divers, for each 15 second interval of measuring. correlation (R = -0,872 for degree of freedom n-2=11
and level of siginificance 5% coeficient is 0,55)
HR and oxygen saturation dependency in static apnea
Correlation of HR and SaO2 changes in apnea
Correlation of HR and SaO2 values at the end of
There is statistically significant linear correlation (R =
0,587 coefficient 0,55 for the level of significance of 5%
and degree of freedom n-2=11).
Physiological breaking point (urge to breath)
Correlation of apnea duration and the moment of
physiological breaking point apnee.
There is linear correlation with statistically significance
R = 0,723 coefficient 0,514 for level of significance 5%
degree of freedom n-2=13.
O. P. Tutorov
It is possible to make apnea profile using the analysis of heart rate values and
oxygen saturation in blood. Apnea is divided into two phases, in relation to physiological
breaking point (the moment when urge to inhale appears). Apnea profile shows the
changes of HR and SaO2 parameters values during apnea. Based on the analysis of apnea
profile we gathered the data about physical fitness of the divers, their tolerance to
hypoxemia and hypercapnia, psychological state during apnea.
Ideal static apnea profile
At the beginning of apnea, saturation value is high (approximately 100%), heart
rate values should be as lower as possible, i.e. ideally between 60-90bpm. A little bit
higher heart rate in relation to standstill condition is the result of respiratory response to
the preparation for apnea. Heart rate values above 90bmp at the beginning of apnea
(especially above 100 bmp) are a negative indicator for apnea duration. It is an indicator
either of hyperventilation or psychological anxiety. In the first half of apnea (easy going
phase) heart rate slows down to the values of 50-60bpm. This is the result of respiratory
rest, i.e. apneustic centre activities. Also, HR reduction in the first apnea phase occurs due
to parasimpaticus predomination.
SaO2 values in the first phase
change a little, and there is a
significant saturation decrease
occurs with the diaphragm
breaking point), which is the
second apnea phase
phase). In the second phase HR
continues to slow down. HR
changes in this phase are the
result of parasimpaticus activities
and hypoxic response of the brain centres to SaO2 reduction. HR increase in the second
apnea phase is the result of inadequate psychological response to urge to inhale (indicator
of bad physical condition).
HR changes in relation to apnea duration
Relation between static apnea duration and HRend values show inversive linear
connection. Shorter apneas end with higher HR values comparing to apneas which last
longer (Figure 1.). The reason for inverse linear correlation of changes of HR values and
apnea duration is diving reflex activation which triggers powerful braycardiac response.
HR reduction in apnea is progressive as time goes by, although there are some deviations.
Shorter apneas with lower values of HR imply good physical condition, deep relaxation
and strong diving reflex activation. Contrary to this, longer apneas with HR increase point
out to psychological tension, as a negative response to CO2 increase and urge to inhale.
HR and oxygen saturation dependency in static apnea
Changes of SaO2 in relation to apnea duration
The relation between static apnea duration and SaO2end values (SaO2 value at the
apnea end) shows statistically significant correlation (Figure 3). Apneas which last longer
have lower values of the SaO2 and vice versa, shorter apneas end with high values of
SaO2. Apnea duration is a variable which directly influences SaO2end values. During
apnea the body consumes oxygen so the longer apneas, the greater oxygen consumption.
The result is lower SaO2end value.
HR and SaO2 changes in connection to physiological breaking point
Physiological breaking point occurs most commonly in the second minute of
apnea, and there is a direct linear correlation between apnea duration and time when the
urge to inhale occurs (Figure 6). Change of SaO2 values in the second apnea phase
indicates larger decrease of values of oxygen saturation in blood. It can be said that when
the physiological breaking point is reached, i.e. during the diaphragm contractions, the
oxygen consumption in apnea speeds up. In the second apnea phase, due to the
occurrence of urges to inhale, muscle contractions accelerate the oxygen consumption.
Also, psychological tension and oxygen consumption in the brain begin to accelerate.
Diving reflex in apnea
Diving reflex gets activated during apnea. We can observe the intensity of the
reflex activation by looking at the intesity of HR reduction. During apnea HR reduction is
progressive. HR reduction at the beginning of apnea is the consequence of respiratory rest
and apneustic centre activities. Quite soon parasimpaticus starts to predominate and the
vagus start to influence HR reduction. In the final apnea phase hypoxic stimulus in brain
centres prolongates HR reduction. Statistically significant correlation of changes of HR
and SaO2 in the second apnea phase has inversive characteristic. Higher HR reduction
triggers smaller SaO2 changes. The consequence is conserving oxygen in apnea, which
represents physiological justifiction of diving reflex existance (keeping homeostasis in
AIDA International. Retrieved February 23, 2011, from www.aida-international.org
Lindholm, P. (1999). Oxygen-conserving effects of apnea in exercising men. Journal of
Applied Physiology, 87(6), 2122-2127.
Lindholm, P. (2009). Physiology and pathophysiology of human breath hold diving.
Journal of Applied Physiology 106, 284-292.
Schagatay, E. (2001). Role of spleen emptying in prolonging apneas in humans. Journal
of Applied Physiology, 90, 1623-1629.
Schagatay, E. (2009). Predicting performance in competitive apnoea diving. Diving and
hiperbaric medicine, 3(2), 88-99.
Submitted March 28, 2012
Accepted June 15, 2012