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NORTH BIOL& 242 - Computer 12 Analyzing the Heart with EKG

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Human Physiology with Vernier 12 - 1Computer12Analyzing the Heart with EKGAn electrocardiogram (ECG or EKG) is a graphical recording of the electrical events occurring within the heart. In a healthy heart there is a natural pacemaker in the right atrium (the sinoatrial node) which initiates an electrical sequence. This impulse then passes down natural conduction pathways between the atria to the atrioventricular node and from there to both ventricles. The natural conduction pathways facilitate orderly spread of the impulse and coordinated contraction of first the atria and then the ventricles. The electrical journey creates unique deflections in the EKG that tell a story about heart function and health (Figure 1). Even more information is obtained by looking at the story from different angles, which is accomplished by placing electrodes in various positions on the chest and extremities. A positive deflection in an EKG tracing represents electrical activity moving toward the active lead (the green lead in this experiment).Although the ECG has great diagnostic value in terms of heart muscle arrthymias, it does not directly show when the atria contract (atrial systole) or the ventricles contract (ventricular systole). The ECG also does not show when the AV values close/open or the semilunar valves close/open. The timing of heart chamber systole and diastole and the shutting or opening of values are inferred rather than directly visualized in an ECG tracing. The “thunk” of the closing of heart valves can be heart as a “lub dub” sounds (known as S1 and S2) by auscultation with a stethoscope.Five components of a single beat aretraditionally recognized and labeled P, Q, R,S, and T. The P wave represents the start ofthe electrical journey as the impulse spreadsfrom the sinoatrial node downward from theatria through the atrioventricular node anddown the interventricular bundle to Purkinje’sfibers in the inferior walls of the ventricles. Actual atrial contraction (systole) iscompleted between the P and the Q peaks.Ventricular activation is represented by theQRS complex. The Q-R interval representsdepolarization of the ventricles after theimpulse has arrived via the S/A node,interventricular bundle, and Purkinje’s fibers. At the R peak, the ventricles begin to contract,with full contraction (systole) sometimebetween the R peak and a bit after the S wave.The T wave results from ventricularrepolarization, which is a recovery of theventricular muscle tissue to its resting state.By looking at several beats you can also calculate the rate for each component. Doctors and other trained personnel can look at an EKG tracing and see evidence for disorders ofthe heart such as abnormal slowing, speeding, irregular rhythms, injury to muscle tissue (angina), and death of muscle tissue (myocardial infarction). The length of an interval indicates whether an impulse is following its normal pathway. A long interval reveals that an impulse has Figure 1Bio 242 Anatomy and Physiology II ECG Lab Using Computer-Assisted Sensors pg. 2been slowed or has taken a longer route. A short interval reflects an impulse which followed a shorter route. If a complex is absent, the electrical impulse did not rise normally, or was blocked at that part of the heart. Lack of normal depolarization of the atria leads to an absent P wave. An absent QRS complex after a normal P wave indicates the electrical impulse was blocked before itreached the ventricles. Abnormally shaped complexes result from abnormal spread of the impulse through the muscle tissue, such as in myocardial infarction where the impulse cannot follow its normal pathway because of tissue death or injury. Electrical patterns may also be changed by metabolic abnormalities and by various medicines.In this experiment, you will use the EKG sensor to make a five second graphical recording of your heart’s electrical activity, and then switch the red and green leads to simulate the change in electrical activity that can occur with a myocardial infarction (heart attack). You will identify the different components of the waveforms and use them to determine your heart rate. You will also determine the direction of electrical activity for the QRS complex. OBJECTIVESIn this experiment, you will- Obtain graphical representation of the electrical activity of the heart over a period of time.- Learn to recognize the different wave forms seen in an EKG, and associate these wave forms with activity of the heart.- Determine the heart rate by determining the rate of individual wave forms in the EKG. - Compare wave forms generated by alternate EKG lead placements.MATERIALScomputer Vernier EKG SensorVernier computer interface (labpro) electrode tabsLogger Pro softwarePROCEDUREPart I: Standard limb lead EKG1. Start computer and plug in Vernier labpro into outlet. Connect the EKG Sensor into CH1 (on the front left side) on the labpro using the white square plug. Use the USB cable to connect the labpro to the computer (The small, square connector plugs into the USB port on the right side of the labpro. The wide connector end plugs into the USB port on the left side of the laptop.)2. Launch the Logger Pro software using the icon on the quick launch toolbar on the bottom of the laptop screen. From the ‘File’ menu, click on ‘Open’ and select “12 Analyzing Heart EKG” from the Human Physiology with Vernier folder.Human Physiology with Vernier 12 - 3Analyzing the Heart with EKG3. Attach three electrode tabs to your arms, as shown in Figure 2. Place a single patch on the inside of the right wrist, on the inside of the right upper forearm (distal to the elbow), and on the inside of the left upper forearm (distal to elbow).4. Connect the EKG clips to the electrode tabs as shown in Figure 2. Sit in a relaxed position in a chair, with your forearms resting on your legs or on the arms of the chair. The graph is automatically setup to collect data for 3 seconds. To extend the collection time press ‘Ctrl+T.’ this will double the set run time for the experiment. When you are properly positioned, have your lab partner click to begin data collection. 5. Once data collection is finished, click and drag to highlight each interval listed in Table 1. 7. Use Figure 3 as your guide when determining these intervals. Enter the -x value of each highlighted area to the nearest 0.01 s in Table 1. This value can be found in the lower left corner of the graph.8. Calculate the


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NORTH BIOL& 242 - Computer 12 Analyzing the Heart with EKG

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