Effect Of Exercise On Arterial Blood Pressure

23 Mar 2015 05 May 2017

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The aim of this experiment is to investigate the effects of different intensity of exercise on heart rate and arterial blood pressure in young healthy human subjects.

Jumping jack exercise is used in this experiment by increasing the frequency of jumping which are 5, 10, 20, 25 and 30 cycles continuously for 5 sessions. The HR and BP were measured before and after the exercise for the study of hypothesis. Data showed that there is an increase in HR and BP among the subjects. Furthermore, with increasing intensity of exercise, the difference between the values before and after exercise also increased. However, diastolic blood pressure did not show any significant difference.

The cardiovascular system is made up of the heart and circulatory system. The heart pumps blood to the organs, tissues, and cells of our body. Oxygen and nutrients are delivered by the blood to every cell of the body. On the other hand, carbon dioxide and waste materials are removed by the blood. It is important to understand the cardiovascular system in order to fully comprehend the physiological effects of exercise on the human body.1

The illustration shows the front surface of a heart, including the coronary arteries and major blood vessels.

The heart is a myogenic muscular organ which acts like a pump to continuously send blood to our body cells. It has the shape of an upsided pear. The heart is located between the lungs in the middle of our chest. It has a double-layered membrane called a pericardium. The pericardium acts to protect the heart. The outer pericardium layer is attached by ligaments to our diaphragm and other parts of our body. The inner pericardium layer is attached to the heart muscle. There exists a coating of fluid separating the two layers of the membrane. This allows the heart to move as it beats and yet still be attached to our body.3

In this project, we would like to study the effects of exercise on heart rate and blood pressure. The formulated hypothesis is that exercise will cause an increase in heart rate, an increase in systolic blood pressure and a slight decrease or fairly constant diastolic blood pressure.

Heart rate

Heart rate is defined by the number of heartbeats per unit time, in minutes. The heart rate of a human being may change depending on the need for oxygen. When oxygen dependency increases, the heart rate increases. When oxygen dependency decreases, heart rate decreases. Heart rate is measured by counting the pulse of the body.4

Blood pressure

Blood pressure is defined as the force applied on the walls of the arteries as blood is pumped throughout the body. Pressure is determined by the force and amount of blood being pumped and also determined by the size and flexibility of the arteries. Blood pressure is affected by many factors such as the individual's daily routine, diet, emotional state and posture.5

Blood pressure is measured by a device called the sphygmomanometer. It measures the magnitude of pressure required to block blood flow through an artery. Pressure is applied by the sphygmomanometer which cuffs a person's arm.6

The ideal blood pressure is below 120 over 80 (120/80). The systolic pressure is the number above and the diastolic pressure is the number below. Systolic blood pressure is defined as the blood pressure when the heart is contracting. Specifically, it is the highest arterial pressure during contraction of the left heart ventricle. Diastolic pressure on the other hand measures the pressure exerted by the heart when the heart is at rest.

The mean arterial pressure is the average blood pressure of an individual. It can be determined by the following formula:

MAP = DP + 1/3(SP - DP)7

SP = Systolic pressure

DP = Diastolic pressure

Protocol

From the group of 14 individuals, one individual is selected to take measurements of blood pressure and heart rate of the remaining 13 individuals. The 13 subjects consist of 3 males and 10 females, with an average BMI of 19.49. Firstly, the heart rate and blood pressure of the first individual was measured. Then, 5 cycles of the modified jumping jacks were performed. After the 5 cycles of exercise was performed, the subject was required to sit in an upright position, where blood pressure and heart rate was measured. The subject was also given 3 minutes as resting time. After the resting period, the first individual carried on with an increment of 5 cycles of the same exercise up until 20 cycles.(i.e.: 5 cycles, 10 cycles, 15 cycles, 20 cycles) This was done with the remaining 12 subjects.

Standardization

Anticipatory period

All subjects were required to sleep at least 7 hours before the day of the exercise. No caffeine and alcohol diet has to be consumed 3 hours before the exercise. Subjects were required to eat one banana and one energy bar cracker 3 hours before the exercise was conducted. Proper sports attire was worn by all 13 participants. 5 minutes of resting period was given to each subject. Subjects were required to sit in an upright position while resting. Hand phones were switched off to avoid interruptions while doing exercise. Laughing and eating are prohibited during exercise for more accurate readings. Lastly, all subjects were in good health during exercise and are not under influence of any drugs.

Exercise period

During the exercise, activities such as laughing, talking and vigorous movements are not allowed. All candidates must keep their hands straight while doing jumping jacks, and must squat completely throughout the course of the exercise. The beat of the metronome was set at 84 beats per minute.

Resting period

All subjects were not allowed to consume any beverages and no other movements were allowed except the exercise mentioned. A resting period of 3 minutes was given to each subject. The same stopwatch was used to measure the resting period.

Heart rate and blood pressure measurement

Only 1 person was assigned to measure the blood pressure and heart rate of the 13 participants. Initial heart rate and blood pressure was performed 1 minute before the exercise was conducted. After conducting the exercise, heart rate and blood pressure was measured immediately. The heart rate was measured first followed by blood pressure. All subjects were required to sit in an upright position while getting their heart rate measured. The same sphygmomanometer and stethoscope were used to measure the subject's blood pressure.

Methods to measure heart rate and blood pressure

Heart rate

Firstly, the palm side of the subject was turned facing up. The index finger was placed on the wrist of the subject, approximately 1 inch below the base of the subject's hand. The index finger is pressed down in the grove between the middle tendons and outside bone. A throbbing pulse should be felt. The number of beats was counted for 30 seconds, and multiplied by 2. This will give a heart rate of 1 minute.8

Blood pressure

The sphygmomanometer was inflated to a little above 180mm Hg. This collapses the major arteries of the arm. Air is released by turning the air valve. The pressure should drop. When the first throbbing sound was heart, the systolic blood pressure was recorded. The sound heard following the first throbbing sound is the sound of blood flowing through the artery of the arm. This means the systolic blood pressure is higher than the pressure in the blood pressure cuff. The air valve continues to be released until no sound is heard. When no more sound is heard, the diastolic blood pressure is recorded.10

Exercise description

Firstly, both feet are put together, with hands down on both sides. Candidates are required to jump to move both feet apart while both hands are raised 90 degrees from the body. They are required to jump again to move feet together and bring both hands together over the head by clapping. The exercise subjects then return to the 2nd position, where both feet are apart and both hands are 90 degrees from the body. Next, candidates then return to the initial position. Lastly, the candidate is required to squat once and then return to position one. Only after performing each of these steps is one cycle considered.

Preparation

Banana, energy bar cracker, metronome and stopwatch were prepared before the experiment.

Type of exercise

The exercise is a modified version of jumping jack. All subjects were required to complete the exercise based on the speed set by the metronome.

Test subjects

3 male and 10 female students were chosen to carry out this experiment. The subjects are healthy individuals who do not smoke and do alcohol. The mean body weight was 57.69kg and the mean height was 165.19cm.

Location of exercise

IMU, Skill's Centre.

Apparatus

Sphygmomanometer, stethoscope, stopwatch and metronome

Interpretation of results

Statistical test

The one-way ANOVA turkey test was used to determine whether there were any difference in systolic blood pressure, diastolic blood pressure, heart rate and mean arterial pressure between the number of cycles of exercise.

Null hypothesis: There is no difference in heart rate, systolic blood pressure, diastolic blood pressure and mean arterial pressure before and after exercise.

Alternate hypothesis: There is a difference in heart rate, systolic blood pressure, diastolic blood pressure and mean arterial pressure before and after exercise. (Heart rate, systolic blood pressure, and mean arterial pressure increases, diastolic blood pressure remains the same or decreases slightly)

Result interpretation

From the results for table 2, it can be seen that the rate of heart rate increases when the number of cycles of exercise increases. Statistically, from the one-way ANOVA turkey test, the calculated p-value for heart rate was lesser than 0.05. If the calculated p-value was lesser than 0.05, this implies that there is a significant difference in heart rate between the number of cycles of exercise. From the graph obtained in figure 1, it can be seen that the heart rate increases steadily when the number of cycles of exercise increases.

From the results for table 3, the result is similar to the result of table 2. Systolic blood pressure increases when the number of cycles of exercise increases. From the one-way ANOVA turkey test, the calculated p-value for heart rate was also lesser than 0.05. This implies a significant difference in heart rate between the numbers of cycles of exercise. From figure 1, it can be seen that the heart rate increases steadily when the number of cycles of exercise increases.

From the results for table 4, the diastolic blood pressure decreases when the number of cycles of exercise increases. From the one-way ANOVA turkey test, the calculated p-value for diastolic blood pressure was also lesser than 0.05. This implies a significant difference in diastolic blood pressure between the numbers of cycles of exercise. From the figure, it can also be deduced that diastolic blood pressure decreases, however only slightly when the number of cycles of exercise increases.

From the results for table 5, the mean arterial blood pressure seems equal throughout the cycles of exercise. When calculating the p-value using one-way ANOVA turkey test, the p-value was higher than 0.05. This implies there is no significant difference in the mean arterial blood pressure between the numbers of cycles of exercise. From the figure, it can also be deduced that the mean arterial pressure doesn't undergo any change as the number of cycles of exercise increases.

Discussion

Effects of Aerobic Exercise on Heart Rate

The heart rate for an individual is 60 to 100 beats per minute. Heart rate per minute will increase depending on the frequency of physical activities the individual carry out. During exercise, muscles undergo aerobic respiration which requires constant oxygen supply. This is because the level of carbon dioxide in the blood increases due to the rising cell respiration of the muscles. Thus, the lack of oxygen results in a huge rush of oxygen intake through the lungs. An impulse is then sent to the sinoatrial (SA) node which causes the heart to beat faster. The increased oxygen intake activates the oxidation of lactic acid into carbon dioxide to be carried away. As a result, the muscles will produce the most amount of energy per mole aerobically.10

Oxygen, carbon dioxide and hydrogen ions (H+) are detected by chemoreceptors which are located at the medulla oblongata and parts of the peripheral nervous system. When exercising, H+ increases due to the excess carbon dioxide. A rise in H+ concentration activates the chemoreceptors which in turn send impulses to the inspiratory centre to increase breathing rate. Hence, heart rate increases. On the other hand, the lack of oxygen also causes a rise in breathing rate. The peripheral chemoreceptors are activated when large oxygen is reduced. Signals are then sent to the inspiratory centre to increase the breathing rate, and thus heart rate.11

Besides, lactic acid which dissociates into lactate and H+ during anaerobic respiration when exercising also results in a rise is H+ concentration. This in turn increases the heart rate by the same mechanism discussed above.12

Heart rate can also be altered by autonomic nervous system. Stimulation of the sympathetic nervous system causes an increase in heart rate as well as other factors such as stroke volume and systemic vasoconstriction.13 The stimulated sympathetic nervous system also acts to release glucose from the liver for energy. During exercise, heart rate rises rapidly due to the activation of sympathetic nervous system.14

Apart from that, the stimulated sympathetic nerves also release catecholamines such as epinephrine and norepinephrine. They work to cause the heart to beat faster by increasing the depolarization of sinus node. This increase of heart rate is known as tachycardia.15 Furthermore, the contractility of the heart muscles will also increase through binding of catecholamines with alpha-adrenegic receptors on the smooth muscles.16

The parasympathetic nervous system opposes the sympathetic nervous system which slows the heart rate especially when physical exertion such as exercise is over. This is due to the release of hormone acetylcholine which hyperpolarizes the membrane and inhibits heart rate. The slowing of heart rate is known as bradycardia.17 When resting after strenuous exercise, both autonomic nervous systems still work continuously to send impulses to the SA node. However, inhibitory is dominance over excitatory. As a result, vagal tone is said to be exhibited by the heart. In addition, if the vagal nerves are not innervating the heart, the heart rate will be slower than it would be.16, 18

Other than that, atrial reflex or known as Bainbridge reflex is initiated during exercise. This reflex involves in increasing the venous return and blood congestion in the atria. By stimulating the SA node and baroreceptor in the atria, the atrial walls are stretched which add on to the force as well as heart rate. As a result, the reflex action leads to a rise in sympathetic stimulation of the heart which in turn increases the heart rate.19

Another factor which contributes to an increase in heart rate is the body temperature. Metabolic rate increases during exercise. This causes the body temperature to rise when the metabolism in the body release energy as heat.15Consequently, sympathetic output at the heart will increase due to the impulses sent by the thermoreceptors to the somatosensory cortex and thus heart rate increase.18

Effect of Aerobic Exercise on Systolic Blood Pressure

In this experiment, 13 subjects were required to perform a modified version of jumping jacks at different intensity levels. The exercise was performed in cycles where increased cycles of jumping jacks will increase the intensity of the exercise.

The mean blood pressure of an individual depends on the amount of blood flow from the heart throughout the body and the net resistance of blood flow in the arteries of the body. Blood pressure is calculated via the following formula:

BP = CO x PVR where,

BP= blood pressure

CO= Cardiac Output

PVR=Peripheral vascular resistance

During exercise, exercising muscles produces more carbon dioxide, thus this increases the blood partial pressure of carbon dioxide (PCO2) in the human body. As PCO2 increases, the need of oxygen intake into the human body increases. Oxygen consumption increases when PO2 decreases. Since oxygen is carried by the blood in the form of oxyhaemoglobin, therefore, the body would need to pump in more oxygen to accommodate for the lack of oxygen.20

From the equation BP = CO x PVR, increase in cardiac output increases blood pressure. As systolic blood pressure is the pressure when the heart is contracting, therefore the systolic blood pressure should increase with increasing exercise.

During exercise, the systolic blood pressure of each experiment subject is seen to be increasing throughout each cycles of the exercise. From the table, it can be seen that the mean systolic blood pressure increased from 106.5 at resting blood pressure up to 135.5 when the exercise was conducted at 20 cycles. Thus, the experiment supports the claim that exercise increases systolic blood pressure.

Effect of aerobic exercise on diastolic blood pressure

Diastolic blood pressure is the blood pressure when the heart is relaxing. It is the blood pressure of our artery walls between heart beats. Diastolic blood pressure is affected mainly by blood volume, stroke volume and heart rate.21

Stroke volume (SV) is the difference between end-diastolic volume (EDV) and end-systolic volume (ESV). It is related by the following equation:

SV = EDV - ESV22

EDV is the volume of blood before the heart contracts and ESV is the volume of blood left in the heart after it contracts. Therefore, SV is the net volume of blood pumped out by the heart in 1 heart beat. During exercise, oxygen consumption increases, therefore the amount of blood needed to pump throughout the body also increases, therefore stroke volume increases during exercise.

During exercise, the temperature of the human body increases. When this happens, the body undergoes negative feedback by dilating the arteries in the body. Vasodilation happens to increase the blood supply to around the tissues and also to take away heat from the body. Therefore, during exercise, cardiac output increases whereas peripheral vascular resistance decreases due to vasodilation. Thus, this causes the diastolic blood pressure to remain fairly constant throughout, or decrease slightly.

From the experiment, the diastolic blood pressure decreases slightly over the course of exercise. As exercise was conducted, vasodilation could explain the lowering of diastolic blood pressure throughout the exercise.

Effect of aerobic exercise on Mean Arterial Pressure (MAP)

MAP is the average pressure of blood exerted on the walls of the arteries during the whole cardiac cycle. MAP is the product of cardiac output and total peripheral resistance. During exercise, cardiac output increases to meet the metabolic needs of skeletal muscles.23Total peripheral resistance on the other hand decreases due to vasodilation of blood vessels. However, total resistance of systemic circulation is kept constant due to constriction of arterioles in visceral organs such as the kidneys and gastrointestinal tract. Therefore, MAP increases in exercise due to the large increase in cardiac output.7

The equation to derive mean arterial pressure is as follow:

MAP = DBP + 1/3 (SBP-DBP)7

Throughout the exercise, systolic blood pressure increases dramatically whereas diastolic blood pressure remains fairly constant or decreases slightly. Therefore, this elevates mean arterial pressure. From the experiment, the mean arterial pressure is fairly constant throughout the experiment. This could be due to the inaccuracy of the measured diastolic blood pressure. Besides that, the exercise could also be switched into a stress test, where subjects are required to perform physical exertion to their limits. A stress test could clearly show mean arterial pressure difference because cardiac output would be at it's maximum.

From the results obtained, it can be seen that the mean arterial pressure is fairly constant throughout the experiment. This could be due to the inaccuracy of the measured diastolic blood pressure. Besides that, the steady decrease in diastolic blood pressure could also override the increase in systolic blood pressure, thus causing the result of mean arterial pressure to remain constant throughout the experiment.

Limitations

Due to the limitations of the experiment, the obtained results were not that consistent and accurate when compared to the theoretical results.

First of all, the sample size is rather too small and insufficient for statistical interpretation as it consists of just 13 members in the experiment.

Gender factor affects the obtained results too. This is due to the imbalance number of females and males in the sample which is 2 males and 11 females. As different genders have different metabolism rate, this contributes to unwanted errors in the results. 10

Other than that, the resting period in between each set of experiment was inadequate due to time constrain. The heart rate and blood pressure were not allowed to return to the resting level before the consequent experiment is carried out.

In addition, due to two different people in measuring the heart rate and blood pressure, it leads to variations in determination of the final readings of the results. There might also be confusion of auditory and visual cues especially when hearing for the diastolic pressure.

Further Studies

In order to improve the studies, a larger sample size can be used to increase accuracy of the results. When a larger sample size is used, more comparisons can be made between the differences of genders, age, BMI, as well as the frequency of exercise.

Besides, the time of the resting period can be modified to be longer. This is to ensure that the heart rate and blood pressure have returned to the resting level before the next set of experiment starts in order to reduce the inconsistency of the results.

Conclusion

From the experiment, the results show that there is an increase in heart rate and systolic blood pressure. However, diastolic heart rate showed a decrease. Calculated mean arterial pressure(MAP) remained constant throughout different exercise intensity. However, this could be due to several reasons discussed as of above.



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