cardiovascular tissue called the cardiac muscle. It

cardiovascular practical




Table of Contents

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The heart consists of a specialized
muscle tissue called the cardiac muscle. It is myogenic – contracting and
relaxing without input from signals of the nervous system. Instead, electrical
impulses passing through the cardiac muscle tissue cause the rhythmic contraction
of the muscle in different parts of the heart.

The sinoatrial (SA) node, located in the myocardium of the right atrium,
acts as a pacemaker, undergoing depolarizations, initiating the process of
contraction. This has an intrinsic rate of contraction a little higher than
that of the rest of the heart muscle. As the cells in the SAN contract, they
generate action potentials which expanse along the muscle in the right and left
atrium walls, inducing muscle contraction – atrial systole. When the action potentials
reach the atrioventricular node (AVN) in the septum, they are delayed briefly.
They then spread down the septum between the ventricles, along fibers called
Bundles of HIS, and then up through the ventricle walls, as can be seen in
figure 1, causing the ventricles to contract slightly after the atria. The
ventricles contract together, from the bottom up – this is ventricular systole.
There is then a brief delay before the succeeding wave of action potentials is
generated in the SAN where the heart muscles relax (diastole).

The purpose of this lab was to
examine the effects of exercise and temperature on the pulse rate and the
contraction of the heart, by studying the heart rate and rhythm, by taking
recording a signal called an electrocardiogram (ECG) which is a measurement of
the electrical activity of the heart causing your heart to contract in a
controlled sequence.

This experiment was conducted to
investigate heart diseases and problems, such as high blood pressure (hypertension)
– which often leads to enlargement of the heart – or evidence of a myocardial
infarction that occurred in the past; abnormal ECG’s can be used to reach
conclusions of the problems with the heart. Furthermore, ECG’s can be used if
disease disrupts the heat’s normal conduction pathways, then changes in the ECG
pattern can be studied for the diagnosis of cardiovascular disease.


We got into groups of 3 or 4.

We took a measurement of the blood pressure using an
automatic sphygmomanometer, by wrapping the cuff around the left upper arm with
the lower edge a couple of centimeters below the antecubital fossa. We use the
left arm because the heart is lateral to the sternum, and closer to the left
arm than the right, so the blood pressure is higher in the left arm, hence is
would make for more accurate measurements.

We took our first blood pressure (BP) measurement at
rest while lying down. The arm was kept at rest on the bed while the cuff
inflated to about 180mmHg. These measurements were taken three times so we
could calculate a mean to make the results more valid.

The second measurement for BP was taken at rest while
standing (immediately after the person got up from a lying down position). This
step was done three times and we calculated the mean.

Then, we recorded our heart rhythms using an ECG for 1
minute at rest, in the sitting position. And selected 3-4 rhythms and printed
them out with scales. We placed two electrode pads on the two clavicles and one
on the last rib on the left side of the body (to allow the electrode to measure
the electrical activity as the blood gets pumped to the rest of the body). The
positive electrode was placed on the last rib, the neutral one was placed on
the left clavicle and the negative one was placed on the right clavicle.

To measure the effect of exercise, one member of each
group exercised on stationary bicycles for 5 minutes and their ECG’s were
recorded immediately after exercise.

One member of each group had to immerse their face in
water. Firstly, their BP and heartrate (HR) was measured at rest in a sitting
position. Their BP and HR were then measured after submerging their face in
cold water. We repeated this step three times, so we could calculate a mean for
the BP and HR in a sitting position and when their faces were immersed.

When we taking the BP and HR’s of every person, we
measured the diastolic, systolic and pulse pressures.


·       Use a larger
cuff on obese of heavily muscled subjects.

·       Use a smaller
cuff for smaller participants.

·       Don’t place the
cuff over clothing.

Flex and support the subject’s arm.



The purpose of measures of central
tendency is to identify the location of the center of various distributions. It
gives us a better idea as to where the center of a distribution is located to
graph the data.

Measures of central tendency:





The mean BP
was calculated using the fomula: 1/3 (sys – dia) + dia


Steps 2-4 produced the results for
the effect of posture on the blood pressure (BP) of the participants.

I used MATLAB to display my results in graphs because it makes it easier
to sort through large amounts of data and plot several variables on the same
graph so I can compare the variables to each other to check for correlation or


I chose to display the data in
scatter graphs as it is the best method to show non-linear patterns with
multiple sets of numerical data. Graph 1 displays the relationship between the
heights of the participants and their mean blood pressure when lying down and
standing up. The independent variable is the heights, so they are plotted on
the x-axis, while the blood pressure is the dependent variable, therefore
placed on the y-axis. The dependent variable depends on the changes in the
independent variable. However, these graphs enhances the fact that BP and HR
are independent to weight and height – there is no correlation between them, so
a change in height or weight does not cause a change in BP or HR.

The standard deviation of the mean
BP while lying down is 8.8288, which is high. A high standard deviation means
that the numbers are spread out, which supports the shape of the graph. The
standard deviation of the mean BP while standing up is 10.6000. Therefore,
there is no correlation between BP and height or BP and weight.

Graphs 1 through 4 show the fact
there weight and height have no effect on the heart rate and therefore no
effect on the blood pressure.



Bar chart

The bar chart displays the results
of investigating the effect of lying down and standing up on the diastolic and
systolic pressure. For lying down and standing up, the systolic pressures should
always higher than the diastolic pressures; this is due to the fact that the
systolic pressure represents the greatest pressure exerted by your heart at
every beat, on the other hand, the diastolic pressure is the pressure in your
arteries when your heart is at rest. The systolic pressures while lying down
are higher than even the diastolic pressures when standing up immediately,
except for participant 12, however this could be an error on the behalf of the

This bar chart shows how postures
and positions we are in affect our HR and BP because we require more or less
blood pumping to our muscles depending on how much movement there is.

Moreover, participants 3 and 12
have higher diastolic pressures than systolic pressures when standing up. This could
be as a result of an infection in the hard, or due to severe impact on the
chest which caused fluid to build up in the pericardium (pericarditis). This
causes the pulse pressure to drop from around 40 to around 0. The difference
between the systolic and diastolic pressure is called the pulse pressure. These
participants may be unaware of the heart condition because teens with cardiovascular
disease (CVD) can have slight symptoms that don’t affect them severely,
allowing them to lead normal lives, unaware of the disease. Common heart problems
facing adolescents include heart murmurs, arrhythmia, enlarged heart and other
problems that result from illnesses.

Normal BP is 120 over 80. Reading
off the graph, participants 5 has a BP of ………….


The blue box represents the values
of the first quartile to the median. The yellow boxes represent the number of
values that fall between the median and the third quartile. The bottom line represents
the smallest value in the dataset. The top line represents the maximum value in
the dataset.

The boxplot displays the effect of
lying down, standing up and facial immersions on heartrate. Plot 1 displays the
heartrates while lying down, plot 2 displays the heartrates while standing up,
and plot 3 displays the heartrates after 5 minutes of facial immersion. Plot 2
has the highest maximum heart rate, while facial immersion has the lowest maximum
heartrate. This could be due to the fact that when you stand up immediately,
all the heartrate has to increase in order to pump more blood around the body
to get to the muscles of the lower limbs so that you don’t collapse when you
stand up. The heartrate decreases after facial immersion due to the fact that
your body goes through homeostasis, where it attempts to prevent a further loss
of heat through vasoconstriction where the arterioles constrict as a result of
contraction of the muscular walls– to reduce the heat travelling near the
surface of the skin. Since the blood vessels are narrowed, the heartrate has to
decrease because there is less body movement and decreased heartrate decreases
the blood pressure so that the walls of the blood vessels are not damaged.

In addition, plot 3 has the lowest
minimum heartrate compared to plot 1 and 3.

Plot 3 has the greatest
interquartile range (IQR) compared to plot 1 and 2, thereby meaning that it has
the greatest distribution of results. The IQR of plot1 is 16.9,



Graphs comparing the blood
pressures between males and females would not be sufficient because there is an
unequal ratio between males and females – there are 2.75 more females than males.
Therefore it would not be a reliable because it is not representative of the

In order to investigate factors
that could be affecting the changes in the heart rates, I conducted a survey
where I asked all the participants of the investigation whether or not they had
eaten that morning or the night before, exercised, and whether they had had any
forms of caffeine.

Blood pressure normally rises as a
result of:

Ø  Stress

Ø  Smoking

Ø  Cold temperatures

Ø  Exercise

Ø  A full stomach

Ø  Full bladder

Ø  Caffeine

Ø  Certain medicines


Factors affecting heart rate:

Body temperature





Caffeine and other drugs



conclusion, height and weight do not affect the heart rates of blood pressures of
the participants, however, different positions and exercises affect them, such
as standing up, lying down and immersing your face in a bucket of cold water.


Figure 1:







Time and date accessed:
Wednesday 6 dec 2017, 9.53 am




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