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Analyse and evaluate the effect of exercise on the ECG trace

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5.3a Analyse and evaluate the effect of exercise on the ECG trace The heart is a hollow, muscular organ which through a muscle contraction generates the force to circulate blood throughout the body. Heart contractions result from a series of electrical potential changes, this is known as depolarization waves. The depolarization waves travel through the heart just before to each beat. (Seeley 2000) Two systems control the effects of the contraction on the heart. 1. The first is the autonomic nervous system, which is situated through the vagus nerve. This nervous system controls the accelerations and decelerations of heart rate. 2. The second system is the intrinsic conduction system which ensures that heart muscle tissue depolarizes in order, e.g. from atria to ventricles, which therefore results in a coordinated heart beat. The intrinsic conduction system is composed of several important components, * The SA (sinoatrial) node, * The AV (atrioventricular) node, * The bundle of His, * Right and left bundle branches * The Purkinge fibres. (Seeley 2000) Fig1 - A diagram of the heart. Featuring the main components of heart contraction adopted from www.qubitsystems.com/human.html In Fig1 it can be seen when the SA node starts the depolarization wave that the components spread the waves from the top, in the atria, down through the ventricles. In a healthy heart, the electrical signal is immediately followed by muscle contraction. The heart is made up of many different muscle fibres each arranged a particular way. So that the muscle fibres are aligned together with a space in the middle of them, they are called chambers and this is where blood sits. When the fibres contract, they exert a force on the wall of the chambers and this decreases the space. The force of the compression on blood puts blood under pressure. This is how blood pressure is developed. There are four chambers of the heart: * Two small atrium chambers * Two large ventricular chambers The atria receive blood from the body back to the heart and the ventricles pump blood from the heart out to the body. ...read more.


This shows that maybe strength training is a better source of exercise for raising systolic blood pressure. Due to the slower heart rate increase on strength training, it is recommended for persons with cardiovascular concerns. By wearing a heart rate monitor, people may safely perform strength exercises within prescribed heart rate ranges, possibly from doctors. Heart rate-monitored strength training is just as important as heart rate-monitored aerobic activity for; cardiac rehabilitation patients, post-surgery participants, elderly exercisers and other high-risk individuals. Aerobic Exercise Blood pressure is controlled by a mechanism known as the baroreflex. This is located in the an artery of the neck, the carotid artery and in the aorta. Here there are a series of pressure sensitive cells known as baroreceptors. These baroreceptors detect the level of blood pressure and relay information to the cardiovascular control centre in the brain. (Brooks et al1992) If there is an error between the measured and required pressure, certain responses occur to correct the difference. For example, At rest whilst sitting, average blood pressure is 120 mmHg systolic and 80 mmHg diastolic. If the individual then stands, blood pressure drops due to the influence of gravity. This reduction in pressure is detected by the baroreceptors and heart rate and cardiac output are elevated such that blood pressure can be returned to its normally value. During exercise the baroreflex remains active in controlling the level of blood pressure. During exercise there are certain changes in the cardiovascular system. The greatest change occurs in blood flow to exercising muscle which, when intense exercise occurs conditions can increase up to 35 times. Such a large increase in blood flow has severe consequences for blood pressure regulation, as the opening of this large circulation can result in a sudden and large drop in pressure. (Brooks et al 1992) At the start of exercise the level of required pressure is set to a higher value in the control centre in the brain. ...read more.


In this graph several important factors can be obtained. The pO2 in the lungs is 100mmHb. At this partial pressure haemoglobin is 100% saturated. This is because blood entering the lungs picks up and binds to oxygen immediately. The pO2 in normal tissues is 40mmHb. At this partial pressure haemoglobin is 75% saturated. Haemoglobin gives up 25% of its oxygen when it reaches the tissues with their lower partial pressure of oxygen. The tissues need the oxygen to function efficiently. Partial pressure is lower in the tissues, because they have used the oxygen to perform the Kreb cycle. They then need to replenish the oxygen. When fully oxygenated blood arrives at the tissue, the lower partial pressure of oxygen causes haemoglobin to give up oxygen to the tissues. (McArdle et al 2001) Only 25% of the oxygen available on the haemoglobin molecule is given to the tissues. This means the haemoglobin is still carrying 75% of the oxygen it picked up in the lungs. The remaining extra oxygen is known as an oxygen reserve. When exercise occurs the tissues suddenly develop a need for more oxygen and the pO2 of the tissues drops below 40mmHg, oxygen starts to separate off the haemoglobin molecules at a very rapid rate. Fig11 shows a very steep incline in the curve between 0 and 40 mm of Hg. This is the extra oxygen, which is used as our emergency supply for times of greater oxygen usage in the tissues, e.g. exercise. The Bohr effect The Bohr Effect plays a main role in oxygen-hemoglobin dissociation curve. Carbon Dioxide diffuses into alveoli when the blood passes through the lungs, this results in a decrease in the blood pCO2 and also decreases hydrogen ion concentration. This moves the dissociation curve to the left. The amount of oxygen that binds with haemoglobin at any given alveolar PO2 increases and provides for greater O2 transport to the tissues. When the blood reaches tissue capillaries, CO2 enters the blood and moves the curve to the right, therefore displacing oxygen from haemoglobin and oxygen delivery occurs at a higher PO2. (Seeley 2002) ...read more.

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