SCUBAPRO-UWATEC HEARTRATE MEASUREMENT,Galileo Sol,Meridian User Manual

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HEARTRATE MEASUREMENT FOR
BETTER WORKLOAD ASSESSMENT

03 - Heart rate measurement during diving
04 - How the heart rate is measured

05 - Resting heart rate - how is it influenced?
06 - Cardiac output, blood pressure and workload
09 - Influence of body position on the heart rate
10 - Change of heart rate through breathing
11 - Heart rate when in apnea
12 - Fluid balance and heart rate
13 - Heartbeat - heat and cold

14 - Why does excitement make the heart race?
14 - Heart rate training indicator
15 - Fitness training and training tips
18 - Glossary

TABLE OF CONTENTS

The heart rate is an important indicator
for arising stress. This has been known
for a long time. The sports industry has
reacted to this and is offering an array of
products for ambitious athletes to analyze
and evaluate their training. Whether
a passionate recreational athlete, a
professional marathon runner or a health­conscious retiree – today a heart rate meter
is almost a standard piece of equipment.
So why not use this technology in diving as
well? With the aid of a heart rate monitor
you can keep an eye on the heartbeat
underwater as well and are thereby able to
make your dives even safer. By monitoring
the heart rate, the workload can be
better assessed and the diver can react
to heightened stress in a timely manner.
Furthermore, by measuring the heart rate
you can specifically train to increase your
endurance in advance.

Since increased exertion while diving
in deep water increases circulation
and this in turn increases the nitrogen
uptake, the heart rate can also be used
to calculate decompression times even
more accurately and make diving even
safer. That’s why the SCUBAPRO computers
don’t just show depth, no-stop times and
the decompression schedule but also
continuously inform the underwater athlete
about his or her own heart rate, i.e. his or her
personal stress, which in turn is factored in
when calculating other dive parameters.

However, there are several factors to
consider when using the heart rate while
diving. This booklet will help you to better
understand the background and thereby
draw the right conclusions from the heart
rate behaviors measured. That way,
you’ll be able to make optimal use of this

innovative technology integrated in most
SCUBAPRO computers.

To make this fitness booklet easy and
quick to use and to make the contents as
readily understandable as possible, the
table of contents consists of frequently
asked questions with regard to heart rate,
fitness and diving. This way, any interested
diver only needs to take a quick glance at
the table of contents in order to find the
chapter that contains the answer to his or
her question.

Listen to your heart!
Written by:
Dr. Uwe Hoffmann
Dr. Tobias Dräger and
Jörn Kießler (editor)

INTRODUCTION

3

HEART RATE MEASUREMENT
DURING DIVING

What exactly is the resting heart rate and
how is it influenced? The resting heart rate is
the heart rate a person has when he or she is
not exerting himself or herself. To determine
its reliably, the resting heart rate should
always be measured under comparable
conditions. Important factors are timing
– usually it is determined in the morning
five minutes after waking up – and body
position. Ideally, the person should remain
lying down in bed during the measurement.
The most reliable results are delivered by
a heart rate monitor in this case as well.
If none is available, you can also count
the heartbeats for 20 seconds and then
extrapolate this to one minute, i.e. multiply
the number by three. However, if you count
the heart rate yourself you should keep in
mind that even counting will influence the
heart rate. The important thing is that the
method of measurement should always be
the same.
On the one hand, the resting heart rate
measured provides you with a value to easily
compare yourself to others. However, the
role of the resting heart rate as an indicator
for the overall workload is much more
important. For exertion both underwater and
on the surface, the resting heart rate serves
as a point of reference in order to assess and
classify acute stress.
Of course, not everyone has the same heart
rate since every person is different. And it’s
exactly these differences that influence the
respective heart rates. For example, age,
body height (not just body position) and the
size of the heart are just three characteristics
that explain the differences between the
values of different individuals. For example,
past exertions on the previous day, diet,
fluid intake, time of day, ambient conditions
(temperature, humidity, altitude), and body
position are all factors that influence the

HEART RATE

5

RESTING HEART RATE ­HOW IS IT INFLUENCED?

There are many ways to measure the
heart rate. As an amateur, you can feel
the heart rate on the lower arm artery or
on the carotid artery, for example, and
count it for a set amount of time – usually
15 seconds. You can also hear a heartbeat
when putting your ear to another person’s
chest. In medical practice the heart rate is
usually captured by a electrocardiogram
(ECG). Every heartbeat produces a
measurable electrical signal. Using at least
two electrodes, one on each side of the
heart, this signal can be measured from the
exterior of the body.

Many heart rate monitors used in sports
apply this technique and incorporate such
electrodes into chest straps. The electronic
devices inside the chest strap search for
the electrical impulse every heartbeat
produces. The registered impulse is
transmitted as a signal to the receiver, e.g. a
heart rate monitor, and then analyzed. For
this application it is essential that the two
electrodes remain in contact with the chest
at all times.

WHILE DIVING

And that’s exactly the measuring principles
used by SCUBAPRO computers as well.
With a waterproof chest strap featuring
two electrodes, the electrical impulse
of the heartbeat can also be captured
underwater.
However, the data is not sent to a simple
heart rate monitor but to the dive computer.
And the computer does exactly the
same thing a heart rate monitor does, for
example, while someone is jogging: it shows
the heart rate the diver is experiencing a
that moment. Of course, it also stores the
data, so that after the dive it is possible

to reconstruct exactly at what point the
workload was especially high or especially
low. One special feature of SCUBAPRO
computers with which no regular heart rate
monitor or traditional dive computer can
compete, is that the diver’s heart rate is
factored into the calculation of the no-stop,
decompression and ascent times. Instead
of relying on a single algorithm, current
personal data is utilized.

To this end, SCUBAPRO computers display
the median heart rate over a set period
of time, e.g. every four seconds. Using this
technique, it is possible to capture the heart
rate at rest and during physical exertion
easily and without much disruption to the
person concerned.

HEART RATE

4

HOW THE HEART
RATE IS MEASURED

Heart rate measurement under

water using the chest strap

heart rate. But also acute changes have
an impact on the resting heart rate. For
example, breathing always plays a role with
regard to the level of the resting heart rate. It
influences the heart rate through its impact
on the blood supply and drainage to and
from the heart.
Among other things, an elevated respiratory
rate – due to excitement for example – also
increases the heart rate. After an exertion,
the heart rate of an endurance-trained
person drops back down to its base level
more quickly than the heart rate of an
untrained person.

WHILE DIVING

The resting heart rate indicates “the lowest
limit” that a diver could reach. Certainly,
no dive is started at the “true” resting heart
rate, since putting on the gear alone is often
strenuous enough to boost it.

200

150

100

50

HF

-2 -1 0 1 2 3 Time

Untrained Trained

Return to base heart rate

dependent on training status

Exertion Recovery

HEART RATE

7

The heart is embedded between the two
lungs and works like a displacement pump:
blood is valve-controlled and sucked in
through the superior and inferior caval vein
via the right heart side , loaded with new
oxygen via the lung, and discharged again
through the large body artery (aorta) via the
left side of the heart.
For the body, the heart rate is really a
secondary factor. There is no place for the
body to capture the heart rate directly.
Similar to a gas pedal in a car, the optimal
heart rate at any given time is determined by
other factors. For example, you would never
drive full speed at rush hour in the city. Nor
would a driver ever crawl along an empty
highway at 20 miles per hour. So, just like the
traffic conditions determine the speed of a
car, supplying the tissue – in particular with
oxygen – is central to the organism. If the
tissue is using up a lot of oxygen, the heart
steps on the gas to pump a certain amount
of blood per unit of time through the tissue.
Therefore, the critical factor is the cardiac
output, that is to say the amount of blood
that is pumped through the body within one
minute of time, for example.
A second factor is the distribution of blood
within the body. This is measured by the

HEART RATE

6

CARDIAC OUTPUT, BLOOD PRESSURE
AND WORKLOAD

An Emergency situation is communicated
to the body by sensors and the central
nervous system. In particular, information
from the central organs, like the brain itself, is
processed. Two compensation mechanisms
are possible:

Locally, better circulation can be

achieved by opening the arterial vessels,
i.e. the body provides the blood with
supply channels that are as large as
possible. To use the car metaphor again:
the body clears the highway for the blood.
This way, it can get to the undersupplied
areas quickly.

Centrally, cardiac output can be ramped

up by increasing the stroke volume and/
or heart rate: the body steps on the gas.

A special measure for the interaction
between local circulation and cardiac
output is the arterial blood pressure. It
determines how fast the blood flows
and therefore how fast substances are
transported back and forth. If the arterial
vessels are dilated and offer less flow
resistance, the cardiac output needs to be
raised to maintain the blood pressure – the
heart rate increases.
If the blood pressure is high, that is if the
vessels are constricted, it’s the other way
around. In this case, the heart rate is
lowered. Keeping these facts in mind, it is
worthwhile to take a closer look at how the
cardiovascular system reacts to increased
muscle activity. Because here, a special
case comes into effect.

MUSCLE ACTIVITY

When muscles are flexed they depress
the nearby vessels, which increases the
vessel resistance. This should lead to an
excessive increase in blood pressure, so the
heart rate should actually slow down as a
result. However, just the opposite happens
because the physical activity triggers
complex processes in the brain, which lead

blood pressure, which can be determined
by the organism based on how much the
vessels are stretched.
The way the system works couldn’t be easier.
As soon as there are signs of insufficient
circulation, compensation mechanisms
are put into action. The body reacts to the
imminent undersupply.

Diagram: Cardiopulmonary

System

to changes in blood pressure. The metabolic
process caused by the contraction, the
metabolites produced and the heightened
impact of the sympathetic nervous system
lead to further changes that cause the
heart rate to increase. Because when the
performance level increases the active
muscles must be supplied with more blood.
Nutrients and especially oxygen have to be
delivered in larger quantities, metabolites,
especially lactic acid and carbon dioxide,
as well as heat have to be removed. This
requires an increased cardiac output.
As the stroke volume ( meaning the amount
of blood that is pumped through the heart
by a heartbeat ) limits the ability to increase
the cardiac output, the greater need is
mainly met by the heart rate. The rule of
thumb is: the heart rate rises proportionally
to the metabolism.

Aortic arch

If the workload is high, more

oxygen needs to be transported
to the muscles, so the vessels are
dilated

In combination with the maximum heart
rate, you can at least define the range within
which the heart rate fluctuates. This way, just
one glance at a SCUBAPRO computer will tell
you how high your level of exertion currently
is, based on completely objective criteria.
Keep in mind however that, particularly
while in the water, it is conceivable that a
heart rate below the actual resting heart
rate can temporarily occur. Why? Simply

because basic environmental variables
change and affect the body when you
plunge into the water. The sum of the effects
described below makes the heart rate slow
down underwater.
This slowdown needs to be considered
when interpreting the changes in heart rate.