1、1Biology 2021: Human Anatomy and Physiology Lab Guide 2Exercise 31: Conduction System of the Heart and Electrocardiography pp. 457-466Learning ObjectivesUpon completing this lab you should be able to: 1. Describe and use the basic techniques of electrocardiography. 2. Obtain an electrocardiogram wit
2、h a three lead electrocardiograph using Biopac computer-interfaced physiology equipment. 3. Describe the relationship between the electrical activity of the heart and the waves and intervals of the ECG. 4. Describe the relationship between the anatomy of the conduction system of the heart and the wa
3、ves and intervals of the ECG. (See Figures 31.1-31.3, p. 458-459 in lab manual and Figures 18.16, 18.17, and 18.18, pp. 696-697 in Marieb.) 5. Describe the relationship between the electrical activity of the heart and the mechanical functions of the heart in pumping blood. (See Figure 18.20, p. 699
4、in Marieb.) 6. List and describe the physiological mechanisms that regulate heart activity. Demonstration of the Normal Cardiac Cycle Introduction to Electrocardiography (ECG)The heart pumps blood through two circuits, the pulmonary circuit to the lungs, and the systemic circuit to the rest of the b
5、ody. The pumping of the heart is initiated within the heart itself, and only modified by external neural and endocrine signals. The intrinsic ability of the heart to beat is due to a system of specialized cardiac muscle cells that form the intrinsic conduction system of the heart. The intrinsic cond
6、uction system cannot be observed when the heart is dissected, but it is illustrated on some of the heart models and charts in the lab. The cells of the intrinsic conduction system are specialized to initiate and conduct action potentials throughout the myocardium of the heart. That is to say, the in
7、trinsic conduction system initiates and conducts the excitation of the myocardium that causes it to contract. The ability to spontaneously initiate an action potential is known as autorhythmicity (also referred to as inherent rhythmicity and automaticity). The cells of the sinoatrial node (SA node)
8、in the wall of the right atrium near the opening to the superior vena cava initiate action potentials at a faster rate than any of the other parts of the intrinsic conduction system; therefore, they set the pace for the whole system. Thus, the sinoatrial node of the intrinsic conduction system is re
9、ferred to as the pacemaker of the heart. 2Once the sinoatrial node depolarizes, the depolarization spreads from one cell to another via gap junctions in the interclated discs of the cardiac muscle and by specialized conduction cells in the atria called the internodal pathways. The action potential i
10、s picked up by the atrioventricular node, located in the inferior portion of the interatrial septum, and is transmitted to the ventricles via the atrioventricular bundle (AV bundle or bundle of His). The atrioventricular bundle splits into the right and left bundle branches which supply the right an
11、d left ventricles, respectively. The bundle branches travel to the apex of the heart and branch off into specialized conduction cells called conduction myofibers (also called Purkinje fibers). These fibers conduct the action potentials to all regions of the ventricular myocardium, thus causing it to
12、 contract. The spread of action potentials throughout the myocardium involves the rapid depolarization of the myocardial cells followed a short time thereafter by their repolarization. The contraction of the myocardium is caused by excitation-contraction coupling in a process very similar to that se
13、en in skeletal muscle. Contraction of the heart is called systole. Since the atria contract slightly before the ventricles we can refer to atrial versus ventricular systole. The relaxation of the myocardium results from the repolarization and relaxation of its cells. When the heart is relaxed it is
14、in diastole. As was the case for systole, we can refer to atrial versus ventricular diastole. The electrical changes in the heart that are so essential to its beating can be detected at the surface of the body with the appropriate equipment. The technique of monitoring the electrical changes in the
15、heart is electrocardiography (ECG) (also called EKG). Electrocardiography (ECG) Electrocardiography is a technique which measures the total electrical activity in the heart during the cardiac cycle. Recall from Biology 2010 that all muscle contractions are triggered by a depolarization of the muscle
16、 cells. Unlike skeletal muscle cells which can contract continuously in tetanus, cardiac muscle cells must repolarize in order to contract again (Note: The Interactive Physiology CD on the Cardiovascular System provides an excellent description of ECG and related topics). The wave of electrical depo
17、larization and repolarization that travels across the myocardium can be monitored by electrodes attached to the skin. These electrodes pick up the electrical signals from the heart that are incidentally conducted through all the tissues and fluids of the body. An instrument called an electrocardiogr
18、aph converts these weak electrical signals into a picture or graph. The electrodes can only detect differences in electrical voltage potential between two points on the body called “leads.“ In theory any two points on the body can serve as leads, but by convention about a dozen specific locations ar
19、e used. In this experiment we will use lead II, one of the three appendicular leads illustrated in Figure 1., and Figure 31.4 , p. 460 in your lab manual. (also posted at each Biopac station) While this procedure is described on pp. 460-466 in the lab manual, this lab guide provides more information
20、 about recording ECG, so follow the instructions below. We will use Biopac to obtain ECGs in this lab. It works like a physiograph except that the ECG data are stored on the computer and can be viewed repeatedly. Each Biopac lesson consists of four steps. First, the equipment is set-up and attached
21、to the student subject. Then, the Biopac computer program is run to carry out the remaining three steps which consist of calibration, recording lesson data, 3and data analysis. When you do Biopac Lessons, the data you collect are stored in the filename you provide at the start of the lesson. You can
22、 come in and review or continue to analyze this data in your file folder on this computer as needed throughout the semester. The instructions for proper setup and use of the Biopac equipment will appear on the computer screen as you work through the lesson. Work in groups of no more than four at the
23、 computer stations. Remember you can work on other lab activities (such as review of heart anatomy, etc.), if you have to wait for a lab computer to become available. Obtain an ECG for each person in the group (if unanticipated technical problems lead to time constraints, your instructor may ask you
24、 to record fewer ECGs and share them with each other). Follow these steps in sequence to complete the lab: I. Setup (starting Biopac, choosing ECG Lesson L05-ECG-1, and attaching electrodes).1. If Biopac is not already running, click on the Biopac Student Lab icon on the computer desktop. 2. Click o
25、n L05-ECG-1 on the Lesson menu. Type in your student folder name. Notice that at the bottom of the Lesson menu is the “Review Saved Data“ option which you select to open your folder and select a data file when you wish to review previously collected data. For example, when you finish collecting your
26、 ECG data, it will be saved in your folder as “yourfoldername-ECG-1“. You can open it and analyze it or review it at a later date without having to attach ECG electrodes again. When the Biopac program starts, it will prompt you with on-screen and step-by-step instructions to follow through the compl
27、etion of the lab. 3. Swab the areas of the skin thoroughly with an alcohol pad. Then attach the electrodes at the cleaned skin sites indicated by the diagram posted at each computer station. Then attach the ECG electrodes. The white (-) electrode is attached to the right forearm, the black (ground)
28、electrode to the right leg, and the red (+) electrode to the left leg. II. Calibration. Have the subject sit in a chair. When the subject is sitting still and relaxed, click on Calibrate. Eight seconds of ECG trace will be recorded on the screen. The tracing should be straight and level except for t
29、he normal P, QRS, and T waves of the cardiac cycle. If the ECG drifts too much (wanders up and down) or seems to have unusual or extraneous waves, click on Redo Calibrate and then click on Calibrate. You may want to have your instructor OK your calibration before proceeding to collect data.III. Reco
30、rd Data. When Calibration is successful, the subject will now record their ECG during four procedures:Procedure 1: The subject should sit with feet propped up on another chair (or reclining on three chairs or the lab table). The subjects arms should be folded across their abdomen, and the subject sh
31、ould be as relaxed as possible. Once the subject is in place, comfortable and still, click on Record. Record about 20 seconds of resting (baseline) data and then click on Suspend. 4Procedure 2: The subject should sit up in the chair with arms at their side and feet on the floor. Then click on Resume
32、. Notice that an event marker in the form of a diamond will be placed on the upper border of the tracing at the point on the ECG where you resumed ECG recording. After 20 seconds, click on Suspend.Procedure 3: The subject, still sitting with folded arms, should breathe deeply and slowly for 1 minute
33、. At the end of one minute, while the subject continues to breathe deeply, click on Resume. There will probably be some unavoidable “drift“ of the ECG from the baseline as a result of the thoracic movements and electrical interference from the breathing muscles. Record another 20 seconds of data whi
34、le deep breathing and then click Suspend. Procedure 4: The subject should stand and run in place vigorously for 1 minute. Then, as soon as the subject is seated and starting to relax, confirm that all electrode leads are still attached and click on Resume to record the subjects cardiac recovery from
35、 exercise. If the subject succeeded in elevating their heart rate significantly, it may take a few minutes for the heart rate to return to pre-exercise levels. Alternatively, you may remove the electrodes during the activity, but if so, you must immediately reattach them after the subject sits down
36、again.Upon successfully recording the above four procedures, click on Done. Biopac will prompt you to confirm that you are done. Click Yes. Biopac will prompt you with “What do you want to do now? Choose “Record from another subject“ if you are not the last person in your group to record their ECG (
37、repeat Parts I-III above for that subject), or you may choose “Analyze current data,“ If you are the last person in your group to record their ECG , then proceed to the steps of Part IV below. Always record data from all subjects in your group first, then come back later to complete their data analy
38、sis. The data is always stored in your student folder and available for later analysis. IV. Data Analysis. Click on Review Saved Data. A dialogue box with all of the saved student files will appear. Click on the “Data Files“ folder where the data files are stored. Select the data file you wish to an
39、alyze. The data will be saved in a file with the name you provided at the outset, but with a file extension of “-L05“. The complete ECG record will appear on the screen. The ECG tracing will be very compressed.1. Set measurement boxes to measure waves and intervals. Near the top of the Biopac window
40、, just below the adjust baseline button, is a toolbar with 5 measurement boxes, each with a pair of drop down menu boxes before it. The drop down menu boxes allow you to select a channel number to use and the specific measurement to make on that channel. We will only use channel 2 in this lesson. Cl
41、ick on the first of the channel boxes and select “delta T“ from the dropdown menu, if this is not already the option selected. Delta T will yield the time difference between the beginning and end of the area you select with the I-beam tool. This I-beam tool will be used to measure the time duration
42、of each of the specified waves and intervals. Set all the remaining channel number boxes to “none.“ 2. Measure time duration of each wave and interval for each of the four procedures you recorded. 5First, click on the Zoom tool button (magnifying glass) on the right and highlight the ECG recorded du
43、ring the first procedure by clicking and dragging over it with the mouse. Select Autoscale waveform from the Display drop down menu to resize the ECG on the screen.Then, using Figure 31.2, p. 458 in your lab manual as a guide, use the Biopac I-beam tool to highlight each interval and segment (PR (=P
44、Q) interval, QRS complex, QT interval, and ST segment) in two successive cardiac cycles. Record each measurement in the journal of your data file by selecting EditJournalPaste (CTRL-M). Calculate and record the mean of the two measurements on each segment and interval in your data journal. Repeat th
45、ese measurements and calculations for the other three procedures.3. Set measurement boxes to measure the heart rate, the Beats per Minute (BPM), for each of the four procedures you recorded. Click on the measurement box and select “bpm“ (beats per minute). 4. Measure the BPM for each procedure. Use
46、the Zoom tool button (magnifying glass) to highlight the ECG recorded during the first procedure. Select Autoscale waveform from the Display drop down menu to resize the ECG on the screen. Highlight with the I-beam tool from the start of one R wave to the start of the next R wave. Paste your bpm mea
47、surement into the journal of your data file by selecting EditJournalPaste (CTRL-M). Repeat for the other three procedures.You should annotate your journal to identify the data segment and measurements recorded there as in the following example for the 1st data segment:First data segment: lying downP
48、R (=PQ) interval1: delta T (sec) xxxxxx2: delta T (sec) xxxxxxAvg. xxxxx QRS interval 1: delta T (sec) xxxxxx2: delta T (sec) xxxxxxAvg. xxxxx QT interval1: delta T (sec) xxxxxx2: delta T (sec) xxxxxx6Avg. xxxxx ST segment1: delta T (sec) xxxxxx2: delta T (sec) xxxxxxAvg. xxxxx End of T to next P1:
49、delta T (sec) xxxxxx2: delta T (sec) xxxxxxAvg. xxxxx End of T to next R1: delta T (sec) xxxxxx2: delta T (sec) xxxxxxAvg. xxxxx BPM: 1: bpm xx.x 2: bpm xx.x Avg BPM: xxx5. Print a representative ECG containing two or three cardiac cycles. When you have completed interval/segment and BPM measurement and data entry into your journal, select a representative section (two or three cardiac cycles at most) of the
