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LAB 15 - Blood Pressure and Electrocardiogram


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beathrt.gif (4940 bytes)Heartbeats are the result of electrical activity in the cells of the heart, and can be detected on the surface of the body. These electrical impulses cause the muscles of the heart to contract and relax in a regular rhythm, creating the pumping action that moves the blood through the body's circulatory system. The electrocardiogram, or EKG, records the patterns of that electrical activity. An EKG is performed by applying six electrodes, called leads, to the skin on different parts of the chest. Another electrodes are applied to each wrist and ankle. The electrodes are connected by wires to the electrocardiograph, the machine that records the heart’s electrical impulses. These electrodes pick up the electrical signal coming from the heart, which is amplified and written out on a paper strip. Each electrode looks at the heart from a different viewpoint, and the electrical waveform is slightly different in each one. The pattern of waveforms in the different leads provides a lot of information about the structure and function of the heart. Different placements and combinations of leads provide different views of the heart, usually 12. Electrocardiograms yield information about the heart rhythm and rate, hypertrophy (thickness of the heart muscle) and chamber enlargement, presence of an old or ongoing heart attack (myocardial infarction), or evidence of impaired blood supply (ischemia), abnormalities in the axis, and the direction of the heart’s electrical flow. This is one of the most informative tests performed upon the heart, and is used routinely in the evaluation of people with high blood pressure.

beathrt.gif (4940 bytes)Three factors help determine blood pressure: the amount of blood pumped from the heart, the volume of blood in the blood vessels, and the capacity of the blood vessels. The more blood pumped from the heart (cardiac or heart output) per minute, the higher the blood pressure. The amount of blood pumped may be reduced if the heart beats slower or its contractions are weakened, as may happen after a heart attack (myocardial infarction). An extremely rapid heartbeat, which can reduce the efficiency of the heart's pumping action, may also reduce the cardiac output, as may other types of abnormal heart rhythms. Each time a nurse or physician takes your blood pressure, they are recording two measurements: your systolic pressure and your diastolic pressure, in units mm Hg. Systolic pressure is the force the heart place on the walls of your blood vessels as it is working/pumping with each heartbeat. Diastolic pressure is the pressure the blood places on the walls of your blood vessels when the heart is relaxed between beats. Both of these measurements are important. A high systolic pressure indicates strain on the blood vessels when the heart is attempting to pump blood into your bloodstream. If your diastolic pressure is high, it means that your blood vessels have little chance to relax between heartbeats.

beathrt.gif (4940 bytes)The purpose of this lab was to do a three lead EKG (limb leads I, II, and III) on ourselves and determine the axis of our cardiac vector during depolarization of the ventricles. We were to also Use the DynaPulse sphymomanometers to measure our BP.

Here is a diagram of a normal 12 lead cardiograph that is usually ran for diagnostic purposes. 

Here is what a normal EKG recording looks like

Here is a three lead (limb leads I, II, and III) of my heart and a determination of the axis of my cardiac vector during depolarization of the ventricles.

Perpendiculars lines(blue) are drawn at plotted points on respective vectorial references lines. A line(red) is drawn from the central point through the intersection of the perpendiculars and this gives the electrical axis. The sum of the QRS in mm in lead I and lead III (or in leads I and II) is determined and plotted on the vectorial diagram below.

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beathrt.gif (4940 bytes)The QRS wave in lead II of my EKG measured: +6mm -1mm = 5mm in lead II
beathrt.gif (4940 bytes)The QRS wave in lead III of my EKG measured: +7mm - 0.5mm =6.5mm in lead III
beathrt.gif (4940 bytes)When ploted on the cardiac vector my electrical axis is 104E, which is just within the normal range.



Used to indirectly determine blood pressure.


NOTE:  My blood pressure data is not available.