Discussion on Average Heart Rate By Krystell Peralta

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Abstract

An experiment was performed to determine the effects of change in position and exercise on heart rate, blood pressure, respiratory rate and respiratory minute volume. Heart rate was measured in three different positions, supine, sitting, and standing, plus staying on a standing position for two minutes and five minutes. Heart rate was also measured after mild exercise, moderate exercise, and two and five minutes post exercise. The same procedure was done to measure the effects on blood pressure, respiratory rate and respiratory minute volume. Results supported the hypothesis which showed that there was an increasing trend when the subject changed positions from supine to sitting and standing, which further increased while standing for a longer period of time; however, except in the respiratory minute volume where the value decreased five minutes post exercise. Results also supported the hypothesis that exercise increased the heart rate, blood pressure, respiratory rate and respiratory minute volume, which further increased with increase in exercise level.

Introduction

Purpose

The purpose of this experiment is to investigate the effects of posture and exercise on circulatory functions, including heart rate, diastolic and systolic blood pressure. As well as, to investigate the effects of posture and exercise on respiratory functions, including respiratory rate and respiratory minute volume.

Background

The cardiovascular system and the respiratory system of the body are the two organ systems that work hand in hand to deliver the essential needs of the body. The cardiovascular system carries the blood that flows through a network of blood vessels that extend between the heart and the peripheral tissues. Specifically, it is the red blood cells that carry oxygen to the organs of the body. On the other hand, it is the respiratory system’s organs that ensure proper ventilation and gas exchange within our body (oxygen and carbon dioxide exchange). The red blood cells transport oxygen from the lungs to the peripheral tissues while simultaneously removing carbon dioxide and other wastes from these peripheral tissues.

The heart acts like a pump that delivers oxygenated blood throughout the body. According to Martini and Nath (1), the heart beats approximately 100,000 times each day, pumping an estimate of 8000 liters of blood. The average heart rate of a person, or the number of times the heart beats per minute, will vary from person to person. However, on the average a 20-year old person should have a target heart rate of 100-170 beats per minute and this range will decrease as a person ages (2).

Under normal conditions, heart rate is adjusted as circulatory demands change by autonomic activity and circulating hormones. These factors then modify the natural rhythm of the heart (1). The heart rate is mainly innervated by the autonomic nervous system, which is subdivided into two functions, parasympathetic and sympathetic.

Located in the medulla oblongata of the brain stem is the cardiac inhibitory centre, which sends signals to the heart through the vagus nerve. This parasympathetic function will then reach the sinoatrial and atrioventricular nodes, which will cause the release of neurotransmitter acetylcholine. In turn, heart rate slows down (3).

On the other hand, the cardiac accelerating centre is located in the medulla and upper thoracic spinal cord. The sympathetic fibres run toward the myocardium where the sinoatrial and atrioventricular nodes, and cardiac cells are innervated. As a result, these sympathetic fibres will trigger the release of norepinephrine, which then increases heart rate and strength of ventricular and atrial contraction (3).

It is also important to note that gravity plays a role in blood flow. As a result of gravity, blood is pulsed downward to the lower extremities when a person is standing. Blood tends to stay closer to the heart without the force of gravity. However, as a direct consequence, it is also more difficult for blood to flow upward and return to the heart and lungs for more oxygen. As a result, the body has evolved by using the leg muscles to function as a secondary pump to effectively counteract gravitational force, which help in the venous return of blood to the heart (4).

Heart rate, also called pulse, directly affects blood pressure as blood pressure is a function of cardiac output and peripheral vascular resistance. Cardiac output is a function of stroke volume, the filling pressure as regulated by sodium homeostasis, and heart rate. Peripheral resistance is mainly regulated at the arterioles level by neural and hormonal inputs that affect constriction and dilation of blood vessels (5).

A major hormone that regulates blood pressure, which is secreted by the kidneys, is called renin. It is transmitted in response to a decrease in blood pressure in the afferent arterioles. Renin is converted to angiotensin, which results to vasoconstriction that then increases peripheral vascular resistance, chiefly in the peripheral arterioles, thus resulting to an increase in the blood pressure. Moreover, the release of aldosterone is caused when renin stimulates the adrenal cortical retinal cells in the glomerulosa. Consequently, aldosterone will exert an effect on the distal renal tubes, leading to an increase in sodium reabsorption while secreting potassium. Pressure is maintained by the increase of fluid in the vascular system as caused by sodium retention (6, 7).

Blood pressure is measured by the systolic pressure and the diastolic pressure, where the value of the former results from the contraction of the left ventricle of the heart, driving blood from the heart, into the aorta and out into the systemic arterial circulation, whereas the latter results from the relaxation of the left ventricle of the heart. Blood pressure can vary in individuals, however, average and healthy blood pressure is around 120/80 mmHg. The first value pertains to the systole, while the second value pertains to the diastole (6).

The body gets its oxygen from the lungs after the air has been filtered by the other structures (such as mucous secretions) of the respiratory system. Oxygen is required for cellular respiration to occur. Without oxygen, the body cannot produce the necessary energy that allows human movement.

Breathing is an involuntary action of the body. Without being conscious, breathing and respiration, occurs all the time. Found in the brain stem is the respiratory control center that constantly monitors oxygen and carbon dioxide levels in the bloodstream. Breathing rate is adjusted to maintain balance and homeostasis in the body, whereas gas exchange corresponds to blood circulation and the metabolic needs of the body (8).

Breathing is regulated by the medulla by monitoring the pH of the cerebrospinal fluid, which in turn determines the carbon dioxide concentration in the blood. Oxygen levels do not greatly affect the breathing control centers unless there is a sudden drop in the concentration of oxygen in the blood. When the medulla recognizes the decrease in pH of the cerebrospinal fluid due to the increase in carbon dioxide concentration levels in the blood, it will send transmissions to the rib muscles and the diaphragm to increase the rate (breathing rate) and extent of breathing (breathing volume). Consequently, carbon dioxide levels will decrease, thus normalizing blood pH, which is typically 7.4 (9). Exercise or any intense physical activity can increase carbon dioxide levels in the bloodstream, acting as a stimulus from major blood vessels for the medulla to detect the increase in blood pH.

Hypothesis

1. If the subject changes position, then there will be a slight change in heart rate because of the change of posture from supine position to sitting and standing position.
2. If the subject changes position, then the blood pressure will also change, because of a direct result of the increase in heart rate.
3. If the subject is subjected to change position, then respiratory minute volume will also increase because of the increased blood flow due to increased heart rate.
4. If the subject performs exercise, then respiratory rate will also increase because the body tries to cope with the heightened need for oxygen in the body.
5. If the subject engages in exercise, then the respiratory minute volume will increase because of a direct result of the increase in respiratory rate.
6. If the subject performs exercise, then the heart rate will increase because there is an increased need for blood to flow to the muscles and oxygen debt.
7. If the subject engages in exercise, then blood pressure will also increase as a direct result of the increase in heart rate, however, all four factors will gradually return to resting rate due to time and because the oxygen debt that accumulates during exercise has been paid back.
8. If the subject engages in exercise , then oxygen saturation will increase  because as blood pressure goes up during exercise, the more oxygen the body needs.

Materials and Method

The procedures and materials are all followed from the VCC Lab Manual (17, p85-111). Changes were made on how long to count for respiration and pulse; instead of 60 seconds to count respiration and pulse, as the lab manual states, respiration and pulse were counted in within 20 seconds

Results

The following graphs show the results accumulated from measuring the heart rate, blood pressure, respiratory rate, and respiratory minute volume in different positions (supine, sitting, standing), with varying time while on standing position, after exercise of different intensities, and several minutes post-exercise.

Figure 1: The Effects of Posture on Heart Rate

As seen in Figure 1, there is a consistent slight increase in the average heart rate as one changed positions from supine to sitting, standing and eventually standing for a two minutes and five minutes, respectively.

Figure 2: The Effects of Posture on Blood Pressure (Systolic and Diastolic)

As seen in Figure 2, there was an increase in the average blood pressure, both systolic and diastolic, as the position was changed. Moreover, there was a slight decrease in blood pressure after the first two minutes of standing, but again increased after five minutes. Blood pressure also increased after performing mild and moderate exercise but decreased post-exercise. Average systolic pressure was greater in the fifth minute post exercise but diastolic pressure was greater in the second minute post exercise.

Figure 3: The Effects of Posture on Respiratory Minute Volume

Figure 3 shows that there is a consistent increase in the respiratory minute volume as there was a change in posture, except after standing for five minutes, where there was a noticeable decrease in average respiratory minute volume among the groups.

 Figure 4: The Effects of Exercise on Average Heart Rate

As seen in Figure 4, there is a noticeable increase in the average heart rate after mild exercise that increases further after moderate exercise. As time elapsed after exercising, average heart rate gradually decreased.

Figure 5: The Effects of Exercise and Recovery on Diastolic, Systolic and Mean Arterial Blood Pressure

Figure 5 shows that there was an increase in the average systole, diastole and mean arterial pressure after exercise occurred. It also shows that the higher the level of the exercise, the higher the difference between resting and exercises blood pressure. Average systole, diastole and mean arterial pressure decreased post exercise.

Figure 6: The Effects of Exercise and Recovery on Respiratory Rate

As seen in Figure 6, respiratory rate increased, as the level of exercise increased. Respiratory rate also decreased as the minutes increase post exercise.

Figure 7: The Effects of Exercise and Recovery on Respiratory Minute Volume

Figure 7 shows that there was an increase in respiratory minute volume after engaging in exercise. The higher the level of exercise, the higher the respiratory minute volume is. This increase will gradually decrease as the minutes post exercise increase.

Discussion

Average heart rate showed change when there was a change in position, with heart rate lowest at supine position, followed by sitting position and highest at standing position. This is consistent with the hypothesis presented at the beginning of the experiment. According to MacWilliam (11), the difference between heart rate in supine and sitting position is due to the hydrostatic influence through the carotid sinus reflex, where bradycardia occurs due to heightened pressure within. This reflex is not always active, thus when it is not, there will be no change in heart rate. According to Grubb and Garabin (12), when a person stands up there becomes an increased gravitational stress which the body has to compensate for to avoid reduced oxygen flow to the brain. For the oxygen supply to remain constant, standing is usually accompanied by an increase in heart rate, the force at which the heart contracts, and the tightening of the blood vessels in the lower part of the body. The combination of the three aforementioned actions will keep the blood pushing upwards, against gravitational force, therefore maintaining blood flow to the brain.

Moreover, Grubb and Karabin’s article (12) has also proven the hypothesis which states that as heart rate increases, blood pressure will also increase. Apart from avoiding the effects of the force of gravity, this is because blood pressure is a function of cardiac output and peripheral resistance. In turn, cardiac output is a function of stroke volume and heart rate. Assuming that peripheral resistance remains constant, the increase in heart rate will also lead to the increase in cardiac output, and vice-versa, which ultimately increases blood pressure as well. Postural changes in the body can significantly affect cardiovascular and respiratory function by increasing or reducing cardiac output, thus significantly affecting the amount of oxygen delivered to the organs of the body.

In such cases where a person stands very still, this could lead to fainting. Fainting, or syncope, is the sudden loss of consciousness. This can be mainly attributed to gravity, which has a critical impact on blood pressure. Gravity helps pull the flow of blood downward to the extremities leading to blood pooling in this area and reduced venous return to the heart. This, in turn, would lead to a reduced cardiac output, thus meaning that there is a decrease in heart rate and blood pressure, triggering mechanisms to compensate for and prevent the drop of arterial pressure. However, in some cases, the body is not able to fully compensate, leading to pressure in the brain to drop to critically low levels. It is the lack of oxygen to the brain that causes fainting. By mechanism of fainting, the body is forced to lie to the ground and ease the blood flow (16).

The increase in respiratory minute volume can be attributed to the decrease in carbon dioxide levels in the blood due to the increase in heart rate and blood pressure. Oxygen and carbon dioxide have an inverse relationship, whereas the increase of one will lead to the decrease of the other. The same is true for the opposite. It is also known that the level of carbon dioxide in the blood has an inverse relationship with respiratory minute volume, thus, when oxygen levels increase in the body, respiratory minute volume also increases.

Respiratory minute volume is the product of respiratory rate and tidal volume. Tidal volume refers to the amount of air moved into and out of the lungs during a normal breath (15), and is a type of respiratory volume, while respiratory rate pertains to the number of breaths per minute. Tidal volume and respiratory rate have an inverse relationship. Whereas both are important, the tidal volume plays a larger role in changes in gas exchange. This is because tidal volume can bring in more oxygen for delivery to the cells and release more carbon dioxide wastes out of the body. Increase in respiratory rate does not always suggest that there is the amount of oxygen inhaled and amount of carbon dioxide exhaled.

During exercise, more energy is needed and utilized, thus there is a heightened need in oxygen to maintain cellular respiration in the body. Also, when a person engages in exercise or physical activity, there is an increase in the carbon dioxide levels in the body that would decrease blood pH making it more acidic. Thus, the when the medulla recognizes the change in pH of the cerebrospinal fluid, it sends signals to the rib muscles and diaphragm to increase rate of breathing. Respiratory minute volume also increases because there is an increase in the amount of oxygen inhaled. Consequently, heart rate and blood pressure will also increase in order to get the oxygen to the muscles and other parts of the body (9).

This supports the hypothesis that exercise or any form of physical activity will increase the respiratory rate, respiratory minute volume, heart rate and blood pressure. However, as the time after post-exercise increases, all four factors will gradually restore to normal resting rate. Their increase occurs as a response to the body’s need to maintain oxygen levels for the body to keep working. It is very common to think that during exercise, we breathe heavily because of the rise of carbon dioxide levels which lowers the blood pH along with the decreased oxygen levels. According to Saladin (10), this statement is untrue. The reason why there is an increase of respiration is other causes such as increase of pulmonary ventilation in accordance to the needs of muscles during exercise. Proprioreceptors of the muscles and joints are stimulated during exercise and sends signals to the brainstem centers. Blood gas values are kept uninfluenced due to the elevated oxygen consumption and carbon dioxide.

Lifestyle factors have a big effect on the cardiovascular and respiratory functions. For an average athlete, being very fit can reduce average heart rate to 40 at resting rate, which means that the heart muscles do not have to work as hard to maintain bodily functions. On the other hand, a sedentary person can have an increased heart rate because the heart has to work harder to contract, requiring a stronger force to the arteries (2). Diet can also significantly have a big impact on heart rate and blood pressure. Eating foods that have plenty of cholesterol (fats), sodium or salt and alcohol, or too little potassium and vitamin D can lead to increase heart rate, due to arterial blocking, and blood pressure (13). In addition, smoking is known to contain many chemicals that can interfere with the body’s mechanism of filtering air and cleaning the lungs (14). It is also known to narrow the arteries, thus increasing blood pressure. Moreover, as one ages, the body may not be able to perform its functions as efficiently as before, but genetics can also play a role, as having certain genes can predispose a person for developing certain diseases such as hypertension and myocardial infarction. All these can lead to inefficiencies in delivering oxygen to the body.

One such inefficiency in delivering oxygen to the body is caused by the difference of blood pressure measure. There are four general categories. Normal blood pressure is below 120/80 mmHg but some doctors may recommend below 115/75 mmHg. Prehypertension is a systolic pressure that ranges from 120 to 139 mmHg or a diastolic pressure ranging from 80 to 89 mmHg. Stage 1 hypertension is a systolic pressure that ranges from 140 to 159 with a diastolic pressure ranging from 90 to 99 mmHg. Stage 2 hypertension is considered the more severe hypertension with a systolic pressure greater than or equal to 160 mmHg coupled with a diastolic pressure of 100 mmHg or higher. High blood pressure is the condition in which the force of the blood against arterial walls is sufficiently high to cause health problems (13).

Possible sources of error in this experimentation include inaccurate measurement of the different variables by the experimenter. Some measuring devices used were new to the experimenters, thus it is possible to have slightly inaccurate measurements. In addition, the sphygmomanometer was a bit difficult to read, which may also result to inaccurate measurements. Moreover, bias may have been present. Given that hypothesis were formulated at the beginning of the experiment, it is possible that one source of error came from expecting particular results thus affecting accurate results measurement. Also, as mentioned previously, biological variation plays a role in altering cardiopulmonary functions, thus averaged results of the sample cannot be assumed to be true for the entire population in the experiment.

Conclusion

Change in position had a slight effect on heart rate, blood pressure and respiratory minute volume. Heart rate values increased from supine position to sitting position and standing position. Blood pressure also showed consistent increase, except in the minutes post exercise. Prolonged standing would also lead to the increase in the value of the three factors, except in the respiratory minute volume where average decreased five minutes post exercise.

There was also a considerable increase in the respiratory rate, respiratory minute volume, heart rate and blood pressure after exercise, which was the body’s mechanism to increase amount of oxygen in the body; moreover, the higher the level of exercise, the higher the values for the four previously mentioned factors. These values gradually decreased to resting phase as minutes elapsed post-exercise.

Works Cited

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Appendix

Table 1. Raw (Uncorrected) Data

Table 2. Computed Data

Table 3. Participants in Each Group