Extended Essay May 2022
An investigation on the mammalian
diving response and its effect on heart
rate
Research question: “How does the activation of the diving reflex by submerging an individual's
face in water at the temperatures of 20,15,10 and 5oC have an effect on their heart rate over a 25
second time period with and without breathing?”
International Baccalaureate Extended Essay
Biology
May 2022
Word count: 4011
,Table of contents:
Introduction …………………………………………………………………………………… 3
Research question ……………………………………….……………………………………… 3
Background ………………………………………………….…………………………………. 3
Hypothesis ……………………………………………………………………………………… 5
Method …………………………………………………………………………………………. 6
Variables ………………………………………………………………………………………… 6
Materials ………………………………………………………………………………………… 8
Scientific method ……………………………….……………………………………………….. 9
Safety precautions ……………………………………………………………………………….10
Data ……………………….…………………………………………………………………….11
Raw data …………………………………………………………………………………………11
Qualitative observations …………………………………………………………………………12
Processed data …………………………………………………………………………………...13
Discussion ………………………………………………………………………………………19
Conclusion ………………………………………………………………………………………19
Evaluation ……………………………………………………………………………………….19
Appendices ……………………………………………………………………………………..21
Works cited ……………………………………………………………………………………..29
2
,Introduction
Research question:
How does the activation of the diving reflex by submerging an individual's face in water at the
temperatures of 20,15,10 and 5oC have an effect on their heart rate over a 25 second time period
with and without breathing?
Background:
The aim of the research question is to investigate the diving reflex and how it acts on the human
heart rate. Temperature of water and respiration are components that trigger the response and
through this research question their effect will be investigated in order to get more insight of how
it operates in the human body. This is relevant in a real life situation to divers since this reflex is
essential for survival while being under water.
When diving a set of physiological responses take place in the human body that override the
basic homeostatic reflexes in order to preserve life in the given circumstances. The face
submersion and breath holding is what triggers the response known as either the diving reflex or
the diving response. This reflex is exhibited strongly in aquatic mammals and is essential for
their survival since it gives them the ability to take long dives when searching for prey. The
response also acts in all air breathing vertebrates including humans. It allows staying under water
for extended periods of time by optimizing respiration. It works by minimizing oxygen use and
contributing to more energy efficient swimming/diving by directing blood flow to the essential
organs meaning the lungs, heart and brain while limiting it's flow to non-essential muscles. In
principle the body becomes a ‘heat-lung-brain’ machine with the goal of survival. The three
components of the reflex are cessation of breath known as apnea, decrease in heart rate known as
bradycardia and peripheral vascular resistance. The three systems involved in the reflex are the
nervous system, pulmonary and cardiovascular system. (“Aquatic Mammals.”).
The response is initially triggered by the peripheral receptors by a neural afferent response
through the terminal nerve in the brain, water flowing over the nasal mucosa during submersion
is an essential factor in inducing the diving response. Water entering the nasal cavity is what will
trigger apnea, the first physiological response making up the diving reflex. The anterior
ethmoidal nerve which are the nerve fibers innervating the nasal mucosa and regions around will
be stimulated by the water entering the nose and cause apnea to inhibit the forgen liquid from
entering the upper respiratory system and pathways causing drowning and death. Chemosensory
cells in the anterior ethmoidal nerve are activated by acyl-homoserine lactones, the cavitation of
3
, these is what also encourages apnea. This happens in order to preserve the function of the lungs
since if water would enter them the larynx would spasm and close cutting of the oxygen supply
to the body or in another case the build up of water in the lungs will lead to pulmonary edema
which adds difficulties breathing (Nunez, Kirsten). During apnea which is indulged in all
mammals that are submerging in water there is a cessation in breathing. Apnea causes the upper
esophageal sphincter involving the cricopharyngeus muscle to fully relax, not allowing normal
breathing. ( Tjoa, Tjoson) There is no movement of the diaphragm muscle which contracts
during inhalation and the initial oxygen volume of the lungs becomes fixed due to the
diaphragm’s constant state of contraction in an apneic species. There is no oxygen entering the
respiratory system resulting in a decline in hemoglobins in the bloodstream. The efferent signal
being transported back from the terminal nerve activates the sympathetic and parasympathetic
nervous system which further activate peripheral vascular construction together with
bradycardia.
The second physiological response that makes up the diving response is an arrhythmias,
specifically bradycardia. This is partially innervated by the anterior ethmoidal nerve responsible
for apnea but the main reason this is part of the diving reflex is due to the body going into
asphyxiation, meaning it is deprived of oxygen. Bradycardia is a condition describing an
abnormally slow heart rate usually below 60 bpm. In this case this occurs with the scope to
preserve the remaining oxygen in the body after apnea takes place. (“Bradycardia.”) When not
inhaling fresh air the body is deprived of oxygen and the hemoglobins in the blood will not be
oxygenated in the lungs so the heart cannot pump oxygenated blood through the body. It has
been proven that even just holding your breath for 30 seconds causes a drop in heart
rate(Madormo, Carrie). When it is induced in the diving response there is an even greater drop
up 25% of the initial heart rate in humans and in some marine species it can drop from 125bpm
to as low as 10bpm during their extended dives. This happens in combination to the mild
bradycardia that already occurs when not breathing and the decreased temperature of the water.
The cold temperature and face submersion cause an increase in vagal activity which is part of the
parasympathetic nervous system as the neural pathway stimulating for intensified bradicardia to
occur. The chemoreceptors that are involved in the induction of bradycardia are located in the
carotid bodies and get activated when the decrease in oxygen happens and the levels drop below
60 mm Hg in combination with the submersion.
The last component of the diving response is an increase in peripheral vascular resistance also
referred to as systeming vascular resistance. Vascular resistance is the pressure friction resistance
that must be overcome by blood cells in order to create a circulation flow while traveling through
the circulatory system. The three factors that determine this are the length and diameter of the
vessels and blood viscosity. In the diving reflex resistance increases in some areas in order to
oppose the flow of blood to non essential tissues for survival and keep it concisely in the heart,
4
An investigation on the mammalian
diving response and its effect on heart
rate
Research question: “How does the activation of the diving reflex by submerging an individual's
face in water at the temperatures of 20,15,10 and 5oC have an effect on their heart rate over a 25
second time period with and without breathing?”
International Baccalaureate Extended Essay
Biology
May 2022
Word count: 4011
,Table of contents:
Introduction …………………………………………………………………………………… 3
Research question ……………………………………….……………………………………… 3
Background ………………………………………………….…………………………………. 3
Hypothesis ……………………………………………………………………………………… 5
Method …………………………………………………………………………………………. 6
Variables ………………………………………………………………………………………… 6
Materials ………………………………………………………………………………………… 8
Scientific method ……………………………….……………………………………………….. 9
Safety precautions ……………………………………………………………………………….10
Data ……………………….…………………………………………………………………….11
Raw data …………………………………………………………………………………………11
Qualitative observations …………………………………………………………………………12
Processed data …………………………………………………………………………………...13
Discussion ………………………………………………………………………………………19
Conclusion ………………………………………………………………………………………19
Evaluation ……………………………………………………………………………………….19
Appendices ……………………………………………………………………………………..21
Works cited ……………………………………………………………………………………..29
2
,Introduction
Research question:
How does the activation of the diving reflex by submerging an individual's face in water at the
temperatures of 20,15,10 and 5oC have an effect on their heart rate over a 25 second time period
with and without breathing?
Background:
The aim of the research question is to investigate the diving reflex and how it acts on the human
heart rate. Temperature of water and respiration are components that trigger the response and
through this research question their effect will be investigated in order to get more insight of how
it operates in the human body. This is relevant in a real life situation to divers since this reflex is
essential for survival while being under water.
When diving a set of physiological responses take place in the human body that override the
basic homeostatic reflexes in order to preserve life in the given circumstances. The face
submersion and breath holding is what triggers the response known as either the diving reflex or
the diving response. This reflex is exhibited strongly in aquatic mammals and is essential for
their survival since it gives them the ability to take long dives when searching for prey. The
response also acts in all air breathing vertebrates including humans. It allows staying under water
for extended periods of time by optimizing respiration. It works by minimizing oxygen use and
contributing to more energy efficient swimming/diving by directing blood flow to the essential
organs meaning the lungs, heart and brain while limiting it's flow to non-essential muscles. In
principle the body becomes a ‘heat-lung-brain’ machine with the goal of survival. The three
components of the reflex are cessation of breath known as apnea, decrease in heart rate known as
bradycardia and peripheral vascular resistance. The three systems involved in the reflex are the
nervous system, pulmonary and cardiovascular system. (“Aquatic Mammals.”).
The response is initially triggered by the peripheral receptors by a neural afferent response
through the terminal nerve in the brain, water flowing over the nasal mucosa during submersion
is an essential factor in inducing the diving response. Water entering the nasal cavity is what will
trigger apnea, the first physiological response making up the diving reflex. The anterior
ethmoidal nerve which are the nerve fibers innervating the nasal mucosa and regions around will
be stimulated by the water entering the nose and cause apnea to inhibit the forgen liquid from
entering the upper respiratory system and pathways causing drowning and death. Chemosensory
cells in the anterior ethmoidal nerve are activated by acyl-homoserine lactones, the cavitation of
3
, these is what also encourages apnea. This happens in order to preserve the function of the lungs
since if water would enter them the larynx would spasm and close cutting of the oxygen supply
to the body or in another case the build up of water in the lungs will lead to pulmonary edema
which adds difficulties breathing (Nunez, Kirsten). During apnea which is indulged in all
mammals that are submerging in water there is a cessation in breathing. Apnea causes the upper
esophageal sphincter involving the cricopharyngeus muscle to fully relax, not allowing normal
breathing. ( Tjoa, Tjoson) There is no movement of the diaphragm muscle which contracts
during inhalation and the initial oxygen volume of the lungs becomes fixed due to the
diaphragm’s constant state of contraction in an apneic species. There is no oxygen entering the
respiratory system resulting in a decline in hemoglobins in the bloodstream. The efferent signal
being transported back from the terminal nerve activates the sympathetic and parasympathetic
nervous system which further activate peripheral vascular construction together with
bradycardia.
The second physiological response that makes up the diving response is an arrhythmias,
specifically bradycardia. This is partially innervated by the anterior ethmoidal nerve responsible
for apnea but the main reason this is part of the diving reflex is due to the body going into
asphyxiation, meaning it is deprived of oxygen. Bradycardia is a condition describing an
abnormally slow heart rate usually below 60 bpm. In this case this occurs with the scope to
preserve the remaining oxygen in the body after apnea takes place. (“Bradycardia.”) When not
inhaling fresh air the body is deprived of oxygen and the hemoglobins in the blood will not be
oxygenated in the lungs so the heart cannot pump oxygenated blood through the body. It has
been proven that even just holding your breath for 30 seconds causes a drop in heart
rate(Madormo, Carrie). When it is induced in the diving response there is an even greater drop
up 25% of the initial heart rate in humans and in some marine species it can drop from 125bpm
to as low as 10bpm during their extended dives. This happens in combination to the mild
bradycardia that already occurs when not breathing and the decreased temperature of the water.
The cold temperature and face submersion cause an increase in vagal activity which is part of the
parasympathetic nervous system as the neural pathway stimulating for intensified bradicardia to
occur. The chemoreceptors that are involved in the induction of bradycardia are located in the
carotid bodies and get activated when the decrease in oxygen happens and the levels drop below
60 mm Hg in combination with the submersion.
The last component of the diving response is an increase in peripheral vascular resistance also
referred to as systeming vascular resistance. Vascular resistance is the pressure friction resistance
that must be overcome by blood cells in order to create a circulation flow while traveling through
the circulatory system. The three factors that determine this are the length and diameter of the
vessels and blood viscosity. In the diving reflex resistance increases in some areas in order to
oppose the flow of blood to non essential tissues for survival and keep it concisely in the heart,
4
