Cardiovascular Report

Published:

Introduction

In an average person the heart beats 70 bpm, this is made up of a systole and a diastole phase in which the heart contracts and relaxes rhythmically. In the diastole phase the atria and ventricles are relaxed, and the blood flows into right and left atria. The valves located between the atria and ventricles are open which allows the blood to flow through the ventricles. The diastole phase can be summarized into four points 1) atrioventricular valves are open, 2) The sinoatrial node (SA) initiates heart contraction and contracts using atrial contraction 3) the atria empty blood into the ventricles and 4) the semilunar valves close preventing the blood to flow back to the atria instead of the ventricles. In the systole Phase the blood is pumped to the arteries by the ventricles contracting. Blood is sent to the lungs via the pulmonary artery by the right ventricle, however the left ventricle pumps blood to the aorta. This phase can be summaried by three points 1) contraction of ventricles,2) antrioventricular valves close while the semilunar vales open and finally 3) blood flows to either the pulmonary artery or the aorta. The heart acts as a pump to provide blood and oxygen needed in the body. Requirement of the heart is it needs oxygen and without it would die. The cardiac muscle which the heart is made of will not be able to repair itself if thrived from oxygen. The image of the cardiovascular system is shown below

Cardiac cycle / measuring cardiac cycle

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The contraction and relaxing of the heart determines the cardiac cycle. A complete cardiac cycle is determined when the heart fills with blood and the blood is then pumped from the heart. The contracting and relaxing of the heart can be shown in two way by, 1) audible sounds and 2) graphical. The audible sounds made by the heart is made when the heart valves are closed. These sounds are referred to as the "lub-dupp" sounds. The "lub" sound is made by the contraction of the ventricles and the closing of the atrioventricular valves. The "dupp" sound is made by the semilunar valves closing. A summary is shown below:

The cardiac output is the amount of blood pumped from the ventricles in one minute. This is worked out by multiplying stoke volume by number of heartbeats. As shown one of the factors that determine the cardiac output is stoke volume . This is the amount of blood pumped from one ventricle of the heart with each beat. To determine the stoke volume you subtract volume of blood in the ventricle at the end of a beat (end-systolic volume) from the volume of blood just before to the beat (end-diastolic volume).

Cardiac Output = Stroke Volume X Number of heartbeats

The greater the volume of blood returned to the heart via the veins, the greater the volume of blood pumped by the heart. A greater force is exerted by the cardiac muscle in the chambers of the heart as more blood joins that blood. This causes stroke volume to increase and inturn also increases cardiac output. Hence, the venous return is even greater and sympathetic stimulation increases the heart rate and contraction force, thus, allowing it to keep up with the excessive volume of blood. This affect on the heart can also be stimulated by adrenaline, a hormone. The force of contraction and stroke volume are also increased to increase the cardiac output. The heart rate and the cardiac output are also affected by many other factors.

Factors affecting heart rate

Temperature - This can have an impact increasing or decreasing the heart rate, which would have an impact on cardiac output. This is because in increasing temperature can increase amount of actions potentials in the heart therefore speeding up the heart rate. For example, a person who is ill suffering from fever will have a increased heart rate to normal, lowering the body temperature will slow down the heart rate. Hormones can also increase rate such as adrenaline, noradrenalin and thyroid hormones. The sex of the individual also effects the cardiac output as woman have more heart beats per minute than men and also children compared to adults. Athletes have a enlarged left side which will increase the cardiac output as the stoke volume is increased.

Blood pressure:

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'Blood pressure is continuously regulated by the autonomic nervous system, using an elaborate network of receptors, nerves, and hormones to balance the effects of the sympathetic nervous system, which tends to raise blood pressure, and the parasympathetic nervous system, which lowers it'

Blood pressure is determined by is the pressure exerted by blood circulating on the walls of blood vessels, the pressure is what is responsible for driving blood from the heart through to the veins. It is us usually measured using a sphygmomanometer and measured in units of mm Hg (mercury in millimetres), the systolic and diastolic are determined by looking out for fluctuations on the scale. The same result can be obtained by listening to the blood pressure using a stethoscope however the results obtained would be close enough but not totally accurate due to human error. To get the blood pressure results the inflatable cuff is tightly wrapped around the arm close to the elbow where the brachial artery lies, this is to stop the blood flow by collapses the artery around 14 0mm Hg. The pressure is slowly lowered (tapping noice is heard), when it reaches a point where the blood just starts to flow is called the systolic phase. As more and more pressure is decreased (increase in loudness of blood flow) the blood flow increases and when the artery is fully opens and no sound can be heard (normal blood flow is silent) , only at this point the diastolic reading can be recorded. The technical name for these sounds is called the Korokoff sounds.

To work out the blood pressure you multiply the cardiac output (force of contraction) with peripheral resistance (diameter of blood vessels). The two most common blood pressure categories are hypertension, and hypotension.

Hypertension

Hypertension (high blood pressure) - is termed a long term (choric) medical condition where the blood pressure in increased above normal. 'The word "hypertension", by itself, normally refers to systemic, arterial hypertension'

Hypertension can split in to two categories, primary or secondary. Primary hypertension is when the cause of the increase in blood pressure can not be found medically, and about 90-95% of all cases are primary hypertension. Primary hypertension can be split into two more categories termed chronic and malignant. Chronic hypertension is when the outcome takes a longtime to develop and malignant is a sudden onset which is very dangerous. Secondary hypertension is the opposite of primary, in this case a cause of the increase in blood pressure is found, such conditions could be due to a kidney disease. This is because long term / persistent hypertension would result to kidney damage, strokes, heart attacks, heart failure and arterial aneurysm, angina. The picture below shows a summary regarding complications of high blood pressure.

Causes and treatments:

Primary hypertension- smoking, obesity (being very overweight), drinking a lot of alcohol, lack of exercise and your diet. It has been shown that if another person in your family has or is suffering from high blood pressure, you also have a higher risk of developing it as well.Secondary hypertension- These can be medically linked and these include: kidney disease, endocrine disease in your body) a narrowing of the aorta or the arteries leading to the kidneys. It also be caused by steroid medicines and the contraceptive pill.

Long-term treatment may be needed for high blood pressure as it isn't curable. Suffering from high blood pressure may result to going to hospital for treatment. E,g kidney damage. In this case haemo-dialysis may be needed where the machine acts as a kidney or the other way may be a transplant. Other than this advise which may be given from your GP to alter your life style eg, stop smoking,change your diet to a low-fat, low-salt diet, that includes fruit and vegetables, cut down on alcohol, exercise and lose excess weight.

Hypotension

Hypotension (low blood pressure) Hypotension is the opposite of hypertension, which is high blood pressure. Hypotension is defined as pressure under 100 mm Hg.

Causes and treatments

Some of the causes include taking drugs to treat high blood pressure (hypertension) especially diuretics and alpha blockers, blood loss or damage to the cardiac muscle caused by acute illnesses, a disease of the adrenal gland (Addison's disease). This results to loss of salt which decreases blood pressure and overall loss of blood due to a serious injury or the loss of fluids due to burns. It is also stated that as you get older arteries become less supple which results to not responding as quickly when you stand, this is called postural hypotension.

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Treatment may not be needed if your blood pressure is normally low. If the subject suffers from postural hypotension, your treatment will be related to the course. For example, if a person is taking drugs to lower blood pressure and the result of this is your blood pressure drops to low, then you may be switched to another drug which will lower blood reassure to a normal level. This only happens when a person taking drugs such as diuretics or alpha blockers. Others ways to improve blood pressure to normal levels without the aid of drugs may include, stand up slowly especially when you first wake up, stay away from strenuous physical activities, wear compression stockings. If on the other hand you have postprandial hypotension, you may be advised lie down after eating and eat regular meals with lower levels of carbohydrate.

Blood pressure control:

The mechanism in which the body keeps the blood pressure contract is called homeostasis, For example, baroreceptors. These provide quick responses. For eg. The stretch receptos which are present in the arterial walls recognise an increase in blood pressure. Signals are sent to the medulla cause peripheral vasodilatation and vagus inhibition of the cardiac output, this decreases the cardiac out and resistance in the arteries. To sum up an increase in blood pressure, blood volume is decreased and so the pressure by causing fluid flows out of the capillary. When things go wrong and the body can't balance the outcome is hypertension and hypotension which further lead to having impact on other parts of the body.

Another mechanism: If blood pressure rises, an increase in fluid filtration in the kidneys occur and therefore, more filtrate leaves the body. This decreases the volume of blood and pressure. It also works for a decrease in blood pressure. Less water is removed in the kidneys. It then goes back to the bloodstream to increase the volume of blood which increases the pressure.

If there is an increase in blood pressure, blood volume is lowered and therefore, the pressure by causing fluid to flow out of the capillary. This is also a fast mechanism but like all the others, the effects only last for a short period of time.

ECG-Electrocardiogram.

'The electrical currents generated in and transmitted through the heart spread throughout the body can be detected with an electrograph. A graphic record of the heart activity is called an electrocardiogram. An ECG is a composite of all the action potentials generated by nodal and contractile cells at a given time and is not, as sometimes assumed, a tracing of a single action potential.' (Marieb)

The process of electrical impulses occurs when an action potential is sent to the sinoatrial node, which then sends an impulse to the atrioventricular node passing it down the purkinje fibres to the Bundle of His which causes the heart to beat. A normal sample of an ECG is shown below.

The general shape of the ECG is due to parts of the cardiac cycle. In the cardiac cycle after the blood has been pushed out of the atria into the ventricle the heart is ready for atrial systole which causes the AV valves to open. After the P wave on the ECG (the first small peak) the atria tend to contract pushing the blood out of their chambers. This allows a rise in the atrial pressure, which carries on pushing the blood out of the atria into the ventricles. The ventricles are now going through their final diastole segment where they will be filled with the maximum amount of blood (end diastolic volume). The atria will then go on to relax and the ventricles will depolarise (QRS complex). Now that the atria are relaxed, the ventricles contract which causes its pressure to rise which close the AV valves. The ventricular pressure rises and exceeds the pressure in the arteries causing the SL valves to open and the blood is pushed into the arteries which cause the pressure in the aorta to reach about 120 mm Hg. This is when the T wave occurs and the ventricles relax. As the blood in the ventricles is no longer compacted the ventricular pressure plummets and blood flows back to the heart causing the SL valves to close.

The P wave represents normal atrial polarisation where the electrical impulse travels from the sinoatrial node to the atrioventricular node spreading from the right atrium to the left atrium. The QRS complex shows one single heart beat due to the depolarisation of the left and right ventricles. The QT interval shows the time difference between the first ventricular depolarisation to the last ventricular repolarisation. This doesn't have a set time as it varies due to different types of medications taken, ECG machines used and the techniques used to take the ECG measurements.

The T waves portray ventricular repolarisation, from the QRS complex till the peak of the T wave it shows the absolute refractory period. The rest of the T wave shows the relative refractory period.

Method:

Recording normal Electrocardiogram

This test records a graphical interpretation of the electrical activity of the heart over a period of thirty seconds. The self adhesive electrodes enable the electrical events of the heart to be examined externally.

Apparatus:

  • Green (earth) self adhesive electrode
  • White (negative) self adhesive electrode
  • Black (positive) self adhesive electrode
  • PC with 'MacLab' program

Method:

Seat the subject comfortably and ensure the subject remains at rest. Attach the green electrode to the subjects left ankle, followed by attaching the white electrode to the right wrist and finally connecting the black electrode to the subjects left wrist. Double click on the Maclab program on the desktop of the PC, press start on the program and record the electrical activity of the heart for 30 seconds. This will result in the electrocardiogram being observed on the monitor of the PC.

Improvements and Limitations:

Recording the electrocardiogram can involve using up to 12 self adhesive electrodes, but in the experiment only 3 self adhesive electrodes were used. Accuracy of the results would have been improved with the more self adhesive electrodes used.

It was discovered that the slightest agitation of the subject would result in the electrical activity of the heart to fluctuate because of this it is highly unlikely the electrocardiogram results recorded can be reliant.

Measuring resting Heart rate and Blood pressure

This experiment will allow the systole, diastole and the pulse rate to be recorded. In this test we have used 2 separate methods involving manual and automatic sphygmomanometer.

Automatic Sphygmomanometer:

Apparatus:

Method:

Tighten the cuff of the automatic sphygmomanometer onto the subjects arm at approximately the same vertical height of the heart. Ensure subject is seated comfortably, is at rest and with the arm supported on a table. Increase the inflation of the cuff until the artery is completely enclosed; this will be signified by a noise occurring from the automatic sphygmomanometer. After roughly 60 seconds the systolic, diastolic and pulse reading can all be recorded from the monitor of the automatic sphygmomanometer. Record the results every 3 minutes for 30 minutes.

Manual Sphygmomanometer:

Apparatus:

  • Manual sphygmomanometer including mercury manometer
  • Stethoscope

Method:

Ensure this experiment is conducted in a silent room. Attach the cuff of the manual sphygmomanometer onto the subject at roughly the same vertical height of the height. Seat the subject so that they are at rest and the arm with the cuff is supported by a table. Place earpieces of the stethoscope into ears and the wide head of the stethoscope onto the left side of the subject's chest. Inflate the cuff so that the artery is fully enclosed, this will be signified by a sound from the manual sphygmomanometer, the meniscus of the mercury manometer reading will represent the systole of the heart and when the sound stops, the new meniscus of the mercury manometer represents the diastole. Count the number of heart beats heard for 60 seconds and this will signify the pulse rate.

Improvements and Limitations:

After using both automatic and the manual sphygmomanometer, it was found that the automatic sphygmomanometer was preferred as results were quicker and easier to obtain as well as being more accurate. The manual sphygmomanometer required a near silent room to hear the heart beat at resting, this was impractical. It is also difficult to ensure that calibration is stable. Therefore the automatic sphygmomanometer will be used throughout the rest of this experiment.

Effects of vigorous exercise on Heart rate and Blood Pressure

In this experiment, the same subject that was used to record resting heart rate and blood pressure will be put through 10 minutes of vigorous cardio exercise. This will involve running up and down a series of steps. After this the systole, diastole and the pulse rate will be recorded using an automatic sphygmomanometer every 3 minutes for 30 minutes after the exercise has been completed.

Apparatus:

  • Automatic sphygmomanometer
  • Stopwatch
  • Stairs

Method:

Ensure the stairs are clear and start the stopwatch. The subject will run up and down the stairs until the stopwatch reads 10 minutes. After this period, the stopwatch will be restarted and the subject will be fitted with the automatic sphygmomanometer and the systole, diastole and the pulse rate will all be recorded. After every 3 minutes the systole, diastole and the pulse rate will be recorded for 30 minutes.

Improvements and Limitations:

In this experiment the results recorded at 0 minutes represent the exact time the exercise was completed. However it is impossible to seat the subject down and record the results using the automatic sphygmomanometer in this time frame; so the actual results will be imprecise. Furthermore the exercise performed may not have as extensive; this will affect results as the exercise may not stimulate the myogenic heart as would have been expected. The exercise performed involved running up and down stairs, this was conducted with other people running up and down the stairs; which is unsafe and could be improved upon by clearing the stairs of all people and ensuring the stairs used remain clear.

Effects of Shock and fear

In this experiment, the subject will experience shock and the systole, diastole and the pulse rate will be recorded using an automatic sphygmomanometer. The shock will be conducted by using a horror clip.

Apparatus:

  • Computer with access to internet
  • Headphones
  • Automatic sphygmomanometer

Method:

First start up the computer and access the internet. The video clip used to shock the subject was http://www.youtube.com/watch?v=l9_N2jHxwf8 . Seat the subject next to the computer screen and allow the subject to put on headphones. Start the clip and as soon as the subject is in shock from the clip record the systole, diastole and pulse rate using an automatic sphygmomanometer. Record the systole, diastole and pulse rate every 3 minutes for 30 minutes. Before this, record the resting pulse rate for 30 minutes with 3 minute intervals.

Improvements and Limitations:

The experiment could have been improved by using a larger screen to watch the video clip and surround sound was possible, as this would have provided a greater shock to the subject. The shock would have also been greater if the experiment was conducted in an empty, silent and unlit room. The experiment was limited in the fact that the shock to the subject was subjective. As well as the inability to record the systole, diastole and pulse rate at the exact time the shock occurred.

Effects of Laughter

The subject will experience laughter and the effects of this to the systole, diastole and pulse rate will be recorded using an automatic sphygmomanometer. Laughter will be experienced by watching standup comedy.

Start up the computer and access the internet. The video clip used to shock the subject was the standup comedian Russell Peters. Seat the subject next to the computer screen and allow the subject to put on headphones. Start the clip and as soon as the subject is in laughter from the clip; record the systole, diastole and pulse rate every 3 minutes for 30 minutes using an automatic sphygmomanometer. Before this, record the resting pulse rate for 30 minutes with 3 minute intervals.

From the ECG it shows that this person's action potentials are all working at a similar rate for the time given as the graph does not show any particular changes and is constant throughout. This suggests that the electrical activity in the heart is also regular and stable. The highest point of the graph occurs at the beginning showing a peak of approximately +0.65 mV. The lowest peak is at 41 seconds of +0.50 mV. This gives a slight different of 0.15 mV between the highest and lowest peak which is known to be normal.

The general shape of the ECG is due to parts of the cardiac cycle. In the cardiac cycle after the blood has been pushed out of the atria into the ventricle the heart is ready for atrial systole which causes the AV valves to open. After the P wave on the ECG (the first small peak) the atria tend to contract pushing the blood out of their chambers. This allows a rise in the atrial pressure, which carries on pushing the blood out of the atria into the ventricles. The ventricles are now going through their final diastole segment where they will be filled with the maximum amount of blood (end diastolic volume). The atria will then go on to relax and the ventricles will depolarise (QRS complex). Now that the atria are relaxed, the ventricles contract which causes its pressure to rise which close the AV valves. The ventricular pressure rises and exceeds the pressure in the arteries causing the SL valves to open and the blood is pushed into the arteries which cause the pressure in the aorta to reach about 120 mm Hg. This is when the T wave occurs and the ventricles relax. As the blood in the ventricles is no longer compacted the ventricular pressure plummets and blood flows back to the heart causing the SL valves to close.

The P wave represents normal atrial polarisation where the electrical impulse travels from the sinoatrial node to the atrioventricular node spreading from the right atrium to the left atrium. On average this lasts for 80ms, for this experiment the P wave lasted for 80-100ms, as it should.

The QRS complex shows one single heart beat due to the depolarisation of the left and right ventricles. This should last from 70-110ms. For this experiment it lasted for 60ms. This is slightly less than normal.

The QT interval shows the time difference between the first ventricular depolarisation to the last ventricular repolarisation. This doesn't have a set time as it varies due to different types of medications taken, ECG machines used and the techniques used to take the ECG measurements.

The T waves portray ventricular repolarisation, from the QRS complex till the peak of the T wave it shows the absolute refractory period. The rest of the T wave shows the relative refractory period. The T wave should last for 160 ms, for this person it lasted for 120 ms.

The reason for there being such a small time interval between the QRS and T wave can be one of many. Some including the fact that the person used for the experiment was a male and males tend to have a shorter time interval than females. The participant may have taken medication beforehand which would also affect heart rate depending on what it is. Age is also another factor although for this experiment it may not be a reason as the participants were all young (under the age of 25) and therefore should have a longer time interval. The participant may also have had conditions including obesity, alcoholism, hypertension or diabetes which could affect the results. To be able to overcome these issues the participant needs to be informed to not take any medication beforehand unless it is absolutely vital, their body type and health problems also need to be taken into account so that anomalous results can be accounted for.

The main reason that could affect the results could have been that only 3 electrodes were used rather than the normal 12. This reduces the different types of electrical impulses that can be measured. Furthermore, a simple lab chart reader was used to record the impulses rather than an electrocardiogram which could have been much more accurate. This could have caused the slight differences between the average results and this experiments result.

Null hypothesis - There is no significant difference between the male diastolic and the female diastolic pressures

Discussion

Individual blood pressure:

Blood pressure after and before exercise:

As shown in tables 2 and 3 and graph 2, the subject had a fairly steady systolic and diastolic reading over the 30 minutes at rest. After exercising, the subjects systolic pressure increased greatly to 137mmHg. After this increase, the systolic readings fluctuated as can be seen in the results.

'EXERCISE causes the activity of the respiratory pump and the activity of the muscular pump to increase which in turn increases sympathetic venoconstriction. This increases diastolic volume and therefore stroke volume increases and this causes cardiac output to increase. ' Human Anatomy and physiology-Elaine Marieb.

The fluctuations however are mainly due to homeostasis. Baroreceptors are stretched during exercise and send a stream of impulses to the vasomotor centre. This input inhibits the vasometer centre causing a decline in systolic readings. This explains the fluctuations in the results. Dilation of the arteries reduces peripheral resistance and this causes a decline in cardiac output. 'Afferent impulses from the baroreceptors also reach cardiac centres where the impulses stimulate parasympathetic activity reducing the heart rate' and this is why after the 30 minutes after exercise, the heart rate decreased.

Effect of laughter on blood pressure

The participant's normal blood pressure varied around 100/61 and table 4 shows that by laughing there was a slight increase in the systole as well as an increase in diastole. This could be due to the fact that laughter increases blood flow and improves the function of blood vessels. As there is more blood flowing through the blood vessels, there's more blood being pumped through and out of the heart. This is the part of the cardiac cycle that is portrayed by the systole readings. Systole shows how fast the blood is being pumped out of the heart by atria and ventricular contractions.

From the results it shows that the systole has increased showing that more blood is indeed being pumped out of the heart. Diastole portrays the period of time when the heart is being filled with blood, meaning that the heart itself is not contracting but is relaxing but it shows the movement of blood through the heart. As diastole has also increased it suggests that more blood is filling up the heart as the flow of blood has increased.

The average pulse rate was about 77 beats per minute. The results also show similar pulse rates with a slight increase suggesting that the blood was being pumped around the body slightly faster than normal. This could be due to the fact that the body was using more energy up by laughing and more oxygen needed to be transported around the body and therefore blood was being pumped around the body faster to restore the used oxygen.

The initial blood pressure after the experiment was 126/82 which was indeed the highest result. This is linked to the pulse rate which was also the highest at 113. This measurement was taken straight after the experiment leaving no resting time in between. Due to this reason, the body did not have any time to recover from the change in blood flow and these results show how the blood flow changed during the experiment. The reasons as to why this happened have been covered in previous paragraphs.

The results for 3 minutes after the experiment are constant throughout till the end of the readings at 30 minutes after the experiment. The results also show a decrease in blood pressure down to 111/82 and pulse at 71 beats per minute. The diastole pressure does not change much as there isn't a big change in the hearts condition when it's filling up with blood, but the systole decreases as well as the pulse rate as the body has had some time to recover and has done so by decreasing the flow of blood. However, this has not reached the resting blood pressure or heart rate as it takes the body much longer, nearly up to an hour or hour and a half to go back to its resting state.

The results also show some fluctuations in the blood pressure with the systole increasing at some points. This could be due to the fact that the body was going through homeostasis and therefore these fluctuations happened due to the body trying to maintain all its functions as well as trying to return back to resting level. Overall, the results show that laughing does not affect blood pressure as much as exercise and it does not have as long lasting effect as exercise either as it doesn't use up nearly as much energy as running does.

Effect of shock and horror on blood pressure

Shock plays a similar role as laughter on blood pressure. Both temporarily affect blood pressure, mainly in the first few minutes. Table 5 shows that as soon as the subject viewed the clip, the systole rose to 135mmHg. The same pattern was seen with the laughter. The blood pressure went back to normal rather than experiencing long lasting effect as the subject did with exercise.

Other factors may influence an individual's blood pressure apart from those mentioned above, such as hereditary, medication, alcohol, lifestyle etc.

Heredity, age and race are examples of factors causing hypertension which are uncontrollable. An individual with parents or close relatives with high blood pressure are more likely to develop hypertension.

Anomalous results may have been measured due to some uncontrollable reasons. These could be due to several factors such as environment; the people surrounding the subject, weather conditions (if a window was open or if it was a cold day would affect a person's blood pressure and ECG reading), natural reflexes such as sneezing, yawning. It could also be affected by the activities of that certain individual before the test was carried out.

The experiment could be expanded and improved by including more tests such as effect of caffeine and nicotine, using subjects of different age groups. A wider range of subjects could be used in future to get more accurate and reliable results.

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