Electrocardiogram Lab
Introduction
Electrocardiograms are used to obtain information about the function of the heart. An ECG is a recording of the electrical activity of the heart made from electrodes placed on the surface of the skin. Salt solutions are good conductors of electricity and can transfer electrical activity to the skins surface. An ECG tracing shows the sum of the electrical potentials generated by all the cells of the heart at any moment (Silverthorn, 1998). Each point reflects depolarization or repolarization of a portion of the heart. Depolarization is the signal for contraction. There are three major components of an ECG: the p waves, which corresponds to depolarization of the atria (Silverthorn, 1998). The qrs complex represents the progressive wave of ventricular depolarization (Silverthorn, 1998). And the t wave, represents the repolarization of the ventricles. When recording an ECG, one active surface electrode is the positive and the other electrode is negative while the third electrode is inactive. These electrodes are known as leads. Twelve leads are now used to record ECG: the three limb electrodes plus the nine more electrodes placed on the chest and trunk. ECG’S recorded from the different lead look different and give information about different regions of the heart (Purves, 1998). An ECG provides information on heart rate and rhythm, conduction velocity, and even the condition of the tissues within the heart. Although obtaining and ECG is simple, interpreting some of its subtleties can be quite complicated.
Purpose
To understand the electrical and mechanical events accociated with an ECG tracing (DiFiori and Jarrell, 1998). To record and interpret ECG tracings under a variety of physiological situations (DiFiori and Jarrell, 1998). To determine how changes in an ECG can lead to changes in the heart rate (DiFiori and Jarrell, 1998).
1). What is the effect of the heart rate on a person who is sitting as opposed to exercising?
Hypothesis
the heart rate is faster in a person who is exercising.
2) What is the effect of the heart rate on a person who is sitting as opposed to a person demonstrating biofeedback?
Hypothesis
the heart rate could be the same if the individual is not totally relaxed, but if the person goes to his or her special place that’s very relaxing for them, the heart while performing biofeedback could be lower than a person sitting down.
Methods
Set up an individual to record a normal ECG by placing a white electrode on the wrist, a black electrode on the right ankle, and a red electrode on the lateral malleolus. Plug the electrodes into port number two and choose lesson five and press setup. The biopac unit will check the leads and adjust the recording on the screen. When your patient is still, press the record button and the biopac unit will record for 60 seconds. If a problem occurs, press the redo button and record again. After the setup is complete, take the heart rate of the patient before each activity. The activities include sitting, lying down, biofeedback, autonomic response, and response to exercise. During each activity, record a ECG and make a record of the intervals and amplitudes.
Results
According to the t-test that compares the heart rate of the sitting and exercise intervals, the person sitting has a lower heart rate than the person exercising. The graph also, support the hypothesis. Also, in the chart and graph that compares the heart rate of a person sitting and performing biofeedback, it shows that a person sitting have a higher heart rate than a person performing biofeedback.
Discussion
During the early p-q intervals of an ecg, the atria and ventricles are relaxed while the ventricles are passively being filled with blood. At the latter end of the p-q interval, atrial contraction occurs forcing additional blood into the ventricles. At the beginning of the qrs interval on an ecg reading, the mitral valve closes and the ventricles are at edv (135ml). During the qrs interval, ventricular contraction occurs increasing the pressure in the ventricle and the aorta. When the pressure continues in the ventricle exceeds the pressure in the arteries, the aortic valve opens and blood is ejected. The increased pressure continues through the t peak. The ventricles are now in esv (65ml) and the aortic valve is closed. Now the ventricles are relaxed causing pressure to fall and the cardiac cycle starts over again. This ecg reading was from a normal tracing. Keep in mind that an ecg is easy to obtain, but there are some subtleties that are very complex.
Bibliography
LITERATURE CITED
Silverthorn, D.U.1998. Human Physiology: An Integrated Approach. Prentice Hall Press. NJ, USA.
DiFiori, R.E. and P.E. Jarrell. 1998. Physiology Laboratory Book. Kendall/Hunt Publishing Company. IA, USA.
Purves, W.K. 1998. Life: The Science of Biology. Sinauer Associates, INC. MA, USA.
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