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Electrocardiography Essay

In a normal human being the heart correctly functions by the blood first entering through the right atrium from the superior and inferior vena cava. This blood flow continues through the right atrioventricular valve into the right ventricle. The right ventricle contracts forcing the pulmonary valve to open leading blood flow through the pulmonary valve and into the pulmonary trunk. Blood is then distributed from the right and left pulmonary arteries to the lungs, where carbon dioxide is unloaded and oxygen is loaded into the blood.

The blood is returned from the lungs to the left atrium by the pulmonary veins. From this step the blood in the left atrium goes through the left AV valve and into the left ventricle. Once more the left ventricle contracts and forces the aortic valve to open, the blood flows through the aortic valve and into the ascending aorta. From these actions blood in the aorta is distributed to all the organs in the body, unloading oxygen and loading carbon dioxide simultaneously.

Lastly, the blood returns to the heart through the vena cava and this process is continuously happening in our bodies (Jimenez L11). The cardiac conduction system is what coordinates the beating of the heart by generating and conducting rhythmic electrical signals. The sinoatrial node (SA) is a cluster of modified cardiocytes found at the junction of the right ventricle with the superior vena cava (A. Jimenez). This is what stimulates the heart beat and sets the heart rate. The atrioventricular node (AV) is located at the lower end of the interatrial septum near the right AV valve. This node acts as an electrical gateway to the ventricles; the fibrous skeleton acts as an insulator to prevent currents getting to the ventricles by any other route” (Saladin pg 727-728). The atrioventricular bundle or Bundle of His is a pathway that electrical signals use to leave the AV node. The Bundle of His soon forks into the right and left bundle branches, which enters the interventricular septum and descends toward the apex or bottom of the heart.

Now because the heart has a rhythmic flow and we know it functions off of electrical signals, there is a machine used to test these signals as they are echoed through the body. The primary function of this machine is to see if there are any anomalies in the hearts conduction system. An electrocardiogram records these electrical signals by placing a pair of very sensitive electrodes on other parts of the body (Schoffstall pg 2). An EKG reading shows three principal deflections above and below the baseline: P wave, QRS complex, and T wave.

The P wave is produced when a signal from the SA node spreads through the atria and depolarizes them. The P wave begins during the PQ segment. This segment represents the time required for impulses to travel from the SA node to the AV node. The QRS complex consists of a small downward deflection, a tall sharp peak, and a downward deflection. It is produced when the signal from the AV node spreads through the ventricular myocardium and depolarizes the muscle. Ventricular systole begins after the QRS complex in the ST segment. Atrial repolarization and diastole also occur during the QRS interval.

Atrial repolarization sends a relatively weak signal that is obscured by the electrical activity of the more muscular ventricles. The T wave is generated by ventricular repolarization immediately before diastole. The T wave is smaller and spreads out more than the QRS complex and has a rounder peak. After the T wave begins a new cycle. During the P wave the atria beings depolarizing. Once the depolarization is complete, ventricular depolarization begins at the apex and progresses as the atria repolarizes this occurs at the QRS complex.

At the T wave the ventricular depolarization is complete, ventricular repolarization being at the apex and progresses. After the ventricular repolarization is complete the heart is ready for the next cycle. Received on April 1, 2012 from Bio 240 Lab PowerPoint on Blackboard. When I did my own EKG lab testing I used the following materials: BIOPAC electrode lead set (SS2L), BIOPAC disposable vinyl electrodes (EL503), Cot, BIOPAC electrodes, Computer Sytem, BIOPAC Student Lab software v3. 0 or greater, and BIOPAC acquisition unit (MP30).

When all these materials are available the computer was turned on and three of the electrodes were placed on the body of my teammate. Two electrodes were positioned on the medial surface of each leg just above the ankle, and the last electrode was on the right anterior forearm at her wrist. When these were attached the subject was asked to lie down on the cot and relax. We then attached her to the EKG machine with three colored cables. The white cable was placed on the electrode on the right forearm, the black cable was placed on right leg and the red cable was attached to the electrode on the left leg.

Once the patient was correctly hooked up to the EKG the BIOPAC Student Lab Program was started. Lesson five is the one we used for this experiment and once it had been chosen we label it and started the experiment. There were four conditions we needed to measure; the first being lying down. The subject was lying down relaxing on the cot. We clicked record and let it run for 20 seconds. The data resembled the chart below. If it did not we would have had to repeat the steps until it did.

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