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Effects of caffeine on the heart by
analyzing heart rates of men and women after physical activity
Gina Martin
Bio230W Section 002
Sashi Gollapudi
April 8, 2013
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Introduction:
According to the National Vital Statistics Reports, the leading cause of death in the
United States is heart disease.1 Heart disease can be induced by many different factors such as,
high cholesterol, stress, poor diet, smoking and family history. Heart disease is defined as a
condition that impairs heart function or circulation of the blood by the heart. One of the most
common types of heart disease is coronary heart disease, which is when the arteries of the heart
harden, blocking blood supply back to the heart for further circulation.2 Coronary artery disease
can often induce a heart attack in patients due to the hardening of the arteries. Other heart
diseases include: angina pectoris, auricular fibrillation, and coronary thrombosis. Heart disease
can be reduced by changes in diet, increase in exercise, and less stressful environment.
The heart pumps nutrients to all parts of the body through a system of veins and arteries
in the body.3 The heart is made up of four chambers which pump blood in and out of this
muscular organ. The muscles of the heart are classified as cardiac muscles, which are unique
when compared to other muscles because they can contract without control of the central nervous
system. The chambers of the heart are separated into two major sections called the superior atrial
chambers and inferior ventricular chambers.
The heart is also further divided into right and left atriums. The right portion of the heart
collects deoxygenated blood from other parts of the body and pumps it into the pulmonary artery
where it goes to the lungs to become oxygenated again. Once the blood is oxygenated by the
lungs it then circulates back up to the heart and enters the left atrium. Diastolic contraction is
when the oxygenated blood moves from the left atrium to the left ventricle. Systolic contraction
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is when the oxygenated blood is pumped through the semilunar aortic valve into the aorta which
eventually will enter systemic circulation.
These diastolic and systolic contraction are the systems used to measure blood pressure.
Blood pressure measures the opening and closing of the valves during diastolic and systolic
contraction.4 High blood pressure can indicate how blocked arteries are in a person’s body. The
instrument used to measure blood pressure is called an sphygmomanometer. A
sphygmomanometer is a cuff with pump that shows the blood pressure. A stethoscope is also
needed in order to differentiate between the diastolic and systolic pressure.
Caffeine is one of the most widely consumed drugs in the world. About 80% of adults
consume at least 3-5 cups of coffee a day.5 Caffeine can be found in many different substances
such as, coffee, tea, chocolate, and energy drinks. Researchers are uncertain as to whether or not
caffeine has a positive or negative effect on the body. A study done by Bennett, Rodrigues, and
Kline found that caffeine caused and increase in systolic blood pressure in both men and women
who had a family history of cardiovascular disease.6 Another study done Astorino, Martin, and
Schachtsiek, compared the effects of caffeine in men with hypertension and without hypertension
while exercising. 7 The results showed that caffeine resulted in an increase in resting, exercise,
and recovery systolic blood pressure, but there was no change in diastolic pressure and heart rate.
Caffeine use was also found to cause an increase in muscle pain and heart rate during exercise, in
a study done by Duncan, M.J. and Hankey, J. 8 Thus, it is believed that caffeine consumption
may increase the risk for cardiovascular diseases.
During this laboratory experiment, participants blood pressures and pulse counts were
taken before and after exercise in order to compare the effects of caffeine on the heart.9 The
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objectives of this laboratory experiment were to collect data from each participant in order for
their resting pulse count and blood pressure to be compared with their values post exercise.
Participants were asked to give their personal history in order to indicate the amount of exercise,
caffeine, and other habits that may affect cardiovascular health that they experienced in a weeks
time, in order for their cardiovascular health to be examined. It is believed that participants who
regularly ingest large amounts of caffeine during a week will have higher blood pressure and
pulse counts, when compared to participants who had moderate to no consumption of caffeine.
Materials and Methods:
Personal History:
This laboratory experiment began with collecting personal history from each participant
in the study. The personal data collected was the following information: age, sex, weight (lbs.),
height (inches), smoking (number of cigarettes a day), caffeine (average servings a day), alcohol
(average servings a week), and exercise (average numbers of days a week). The data was charted
on a computer, so it could later be charted with additional data for comparison.
Resting Pulse Count and Blood Pressure:
Next, each individual collected their own resting heart rate by placing their index and
middle fingers on the neck or wrist and counting the amount of pulse counts in thirty seconds.
This was repeated three times for each individual to get an average thirty second pulse count.
The average pulse count was then multiplied by two to get the resting heart rate in beats per
minute.
The resting blood pressure was also collected for each individual using a
sphygmomanometer and a stethoscope. To measure resting blood pressure the brachial artery on
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the arm is located in order to determine where to attach the sphygmomanometer. The cuff was
then wrapped around the individuals arm so it is above the elbow crease, making sure that the
valve on the bulb remains closed. The upper arm must be level with the heart in order to get a
accurate reading. The stethoscope was then placed under the cuff where the artery is located and
the bulb was then squeezed to apply pressure to 200mm. The valve was then released slowly
until a fait thump was heard, which was the systolic pressure. When the sound disappears
completely the diastolic pressure has been found. Both these values are recorded as systolic over
diastolic.
Exercise Pulse Count and Blood Pressure:
For participants shorter than 5 feet 6 inches a box that was 33cm high was used. If
participants were taller than 5 feet 6 inches then a 40 cm high box was used for the exercise. A
single exercise consisted of taking one step with one leg onto the box, another step with the other
leg so the whole body was on the box. Then stepping down off the box with one leg, and finally
stepping down with the other. This exercise was done at two different speeds 15 steps per minute
and 30 steps per minute for one minute each time. After the participants completed the exercise
they sat down and after 15 seconds began taking their own pulse. Their blood pressure was taken
after the 15 seconds had passed. This was repeated for everyone in the group at both speeds.
Data Collection:
After the class had finished the exercise portion of the experiment, the data was then
placed on a chart so it could be combined with additional data. One category of data was chosen
for analysis. For this study, pulse count and blood pressure of participants that drank caffeine
were compared with participants who did not drink any caffeine.
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Results:
The resting levels values in Table 1(see below) and in the Resting Level Values graph(see
below) showed no significant difference in pulse rate between the caffeine and no caffeine
groups. The average systolic blood pressure in the caffeine group was 125.19 mm Hg, while the
value for the caffeine-less group was 121.912 mm Hg. The values for average diastolic blood
pressure was 76.234 mm Hg, while the caffeine-free group was 72.5455 mmHg. The p-values for
these results was 0.445 for the pulse count data, 0.137 for the systolic blood pressure data, and
0.162 for the diastolic blood pressure data.
The normalized average change in pulse count after exercise was depicted in Table 2 and
Graph 2. The average pulse count for the caffeine group was 12.75 beats per minute during the
15-step exercise and 43.72 beats per minute during the 30-step exercise. The average pulse count
for the no caffeine group during the 15-step exercise was 21.27 beats per minute and 48.77 beats
per minute for the 30-step exercise. The p-value for the 15-step exercise was 0.065, while the pvalue for the 30-step exercise was 0.494.
Table 3 and Graph 3 depicted a normalized average change in systolic blood pressure
after exercise. The average percentage difference for the systolic blood pressure in the caffeine
users was 131.44 mm Hg for the 15-step exercise and 144.74 mm Hg for the 30-step exercise.
While the average percentage difference in systolic pressure for the no caffeine group was
132.03 mm Hg for the 15-step exercise trial and 144.697 mm Hg for the 30-step exercise. The pvalue for the 15-step exercise was 0.882 and the p-value for the 30-step exercise was 0.97.
Lastly Table 4 and Graph 4 showed the average percentage difference for diastolic blood
pressure. The average percentage difference for the diastolic blood pressure for the caffeine
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group was 74.89 mm Hg for the 15-step exercise and 76.744 mm Hg for the 30-step exercise.
The average percentage difference for the caffeine-free group was 75.27 mm Hg for the 15-step
exercise and 77.57 mm Hg for the 30-step exercise. The p-value for the 15-step exercise was
0.874 and the p-value for the 30-step exercise was 0.162.
Table 1: Resting level values:
Average
caffeine no caf
Pulse count 36.2166 35.38697
Sys.BP
125.1915 121.9118
Dias.BP
76.23404 72.54546
SE
caf
0.740089
1.907102
1.880376
SD
no caf
caf
0.788588 5.0737908
1.691007 13.074433
1.809639 12.891205
no caf
4.53009
9.71409
10.3956
Graph 1: Resting Level Values
Resting Level Values
130
98
65
33
0
Pulse count
caffeine
Sys. BP
Dias. BP
no caffeine
The results of Table 1 and Graph 1 showed that there was no significant increase or
decrease in average pulse count in the caffeine and no caffeine groups. The average systolic
pressure for the caffeine group was slightly higher than what was experienced in the no caffeine
group. The average diastolic pressure was also slightly higher in the caffein group than in the no
caffeine group.
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Graph 2: Normalized Average Change in Pulse Count/ 30sec After Exercise
Pulse Count
60
45
30
15
0
Caffeine
15-Steps
No Caffeine
30-Steps
Exercise Data:
Table 2: Normalized average change in pulse count/30sec after exercise
av. % diff
SE
sd
no caf
caffeine
no caf
caf
no caf
Pulse count caffeine
15-steps
12.753
21.276
3.0638
3.372
21.004
19.369
30-steps
43.723
48.77
4.4303
5.8603
30.372
33.665
Table 2 and Graph 2 examined the results for the average change in pulse count after
exercise. The no caffeine group experienced a larger increase in pulse count after exercise than
the caffeine group.
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Graph 3: Normalized Average Change in Systolic BP After Exercise
Systolic BP (mm Hg)
150
143
135
128
120
Caffeine
15-Steps
No Caffeine
30-Steps
Exercise Data:
Table 3: Normalized average change in systolic BP after exercise
av. % diff
SE
sd
Sys.BP
caffeine
no caf
caf
no caf
caf
no caf
15-steps
131.446
132.03
2.288
3.19
15.683
18.35
30-steps
144.74 144.697
2.299
2.971
15.764
17.069
Table 3 and Graph 3 showed no significant differences between the caffeine and the no
caffeine groups. The average percentage difference for the 30-step exercise was actually the
same number.
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Graph 4: Normalized Average Change in Diastolic BP After Exercise
Diastolic BP (mm Hg)
80
78
77
75
73
Caffeine
15-Step
No Caffeine
30-Step
Table 4: Normalized average change in diastolic BP after exercise
av. % diff
SE
SD
Dias.BP
caffeine
no caf
caf
no caf
CAF
NO caf
15-steps
74.894
75.273
1.624
1.7338
11.134
9.96
30-steps
76.745
77.576
1.577
1.834
10.810
10.539
Table 4 and Graph 4 shows the average change in diastolic blood pressure after exercise.
The difference between the average blood pressures were so close they were proven
insignificant. The standard error for the diastolic blood pressure was also too large to prove any
significance.
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Discussion:
The results of the analysis of the data collected from the analysis of caffeine’s affects of
the heart are unclear. The average resting level values in table 1 showed no significant difference
in the average pulse rate, but did show a difference in the systolic blood pressure and the
diastolic blood pressure. The systolic blood pressure in the caffeine group was 125.19 mm Hg
while it was only 121.912 mm Hg for the caffeine free group. The diastolic blood pressure was
76.23 mm Hg for the caffeine group and 72.54 mm Hg for the caffeine-free group. Thus, the
average resting heart rate was higher in individuals who had caffeine in their diet, but the pulse
count was not affected.
The normalized average change in pulse count(table 2) showed a increase in pulse count
in participants whom did not consume caffeine. The value increased in both the 15-step and the
30-step exercises for the caffeine-free group. Thus, caffeine consumption could cause the pulse
count to decrease while engaging in physical activity.
The normalized average change in systolic(table 3) and diastolic (table 4) pressure after
exercise showed no significant increase in the systolic group or the diastolic group from the
caffeine consumers and the caffeine-free group. There was also a very large standard errors for
the diastolic group, proving some statistical insignificance.
The p-values for all of the data collected were above 0.05 making the data statically
insignificant for the experiment. These values could have been improved by making a more strict
requirements for caffeine drinkers, such as having to consume X amount of caffeine in a week.
There should have also been more strict restrictions on being in the caffeine free group, such as
having to consume less than X amount of caffeine a week. This would provide data on people
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who definitely fit the criteria of being in either the caffeine group or the caffeine-free group.
Another improvement that would have made the data more statistically significant would have
been to have taken into consideration people’s personal history for factors that would cause stress
on the heart that could alter the data.
In conclusion, although the p-values prove the data to be statistically insignificant the
study proved the hypothesis that caffeine consumption would increase pulse rate and blood
pressure to be false. Further statistically analysis needs to be done to completely accept this
rejection of hypothesis because of the insignificant p-values. Improvements that need to be done
to improve the results would be to use certified personnel to take the blood pressure and pulse
rates so more accurate data can be received and to take into consideration family history for heart
disease. According to other studies done this data is not cohesive, which intensifies the need for
further research with more accurate analysis. Since there is such a large amount of the population
which consumes caffeine, additional experiments need to be done with finer search criteria to
provide a more accurate description of the results.
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References:
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National Vitals Statistics Report. 60,3. December 2011.
2. Braus, Patricia. "Heart Diseases." The Gale Encyclopedia of Science. Ed. K. Lee Lerner and
Brenda Wilmoth Lerner. 4th ed. Vol. 3. Detroit: Gale, 2008. 2081-2083. Gale Virtual
Reference Library. Web. 3 Apr. 2013.
3. Lerner, Brenda Wilmoth, K. Lee Lerner, and Larry Blaser. "Heart." The Gale Encyclopedia of
Science. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. 3rd ed. Vol. 3. Detroit: Gale, 2004.
1934-1939. Gale Virtual Reference Library. Web. 3 Apr. 2013.
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Senagore. Vol. 3. Detroit: Gale, 2004. 1350-1352. Gale Virtual Reference Library. Web. 4 Apr.
2013.
5. Klein, L.C. (2013). Pharmacological influences on health [Word document]. Retrieved from
Lecture Notes Online Web site: https://cms.psu.edu
6. Bennett, J.M., Rodrigues, I.M., Kline, L.C. (2013). Effects of Caffeine and Stress on
Biomarkers of Cardiovascular Disease in Healthy Men and Women with a Family History of
Hypertension. Stress Health.
7. Astorino,T., Martin, B., Schachtsiek, L. (2011) Caffeine Ingestion and Intense Resistance
Training Minimize Postexercise Hypotension in Normotensive and Prehypertensive Men.
Research in Sports Medicine. 21-1, 52-65. Online.
8. Duncan, M.J., Hankey, J. (2013) The effects of a caffeinated energy drink on various
psychological measures during submaximal cycling. Physio Behavior. Web.
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9. “Cardiovascular Physiology: The Relationship between Gas Exchange and Cardiac Activity.”
Edited by Nelson, K. and Burpee, D. Department of Biology, The Pennsylvania State
University, University Park, PA. (2013)