At the end of the 19th century, medical instruments were not able to detect the
ID: 38988 • Letter: A
Question
At the end of the 19th century, medical instruments were not able to detect the cardiac signal unless the electrodes were directly placed into the heart.
1. What is the rage of amplitude of normal EKGpotentials?
2. By what factor is it necessary to amplify the normal EKG signal so that it is easy to record?
3. What sampling frequency is necessary for acquisition?
4. Problem
A. How long does it take for EKG electrical events in the atrium and in the ventricles to occur?
B. What is the duration for each of these EKGwaves? B. State the meaning of each of the wave in the electrocardiogram?
5. How does Willen Einthoven
PLEASE SHOW ANY AND ALL WORK At the end of the 19th century, medical instruments were not able to detect the cardiac signal unless the electrodes were directly placed into the heart. 1. What is the rage of amplitude of normal EKGpotentials? 2. By what factor is it necessary to amplify the normal EKG signal so that it is easy to record? 3. What sampling frequency is necessary for acquisition? 4. Problem A. How long does it take for EKG electrical events in the atrium and in the ventricles to occur? B. What is the duration for each of these EKGwaves? B. State the meaning of each of the wave in the electrocardiogram? 5. How does Willen Einthoven's string galvanometer solve the problem of precision and sensitivity? 6. How did Einthoven and Lewis design their electrodes for the machine? 7. What was the mechanical system utilized to register the signal of the Einthoven and Lewis machines? 8. Name the following EKG abnormalities: 9. Assign to each axis, the corresponding dipolar or monopolar lead (all 6 leads): 10. Problem: A. Calculate the voltage for Leads I, II and III given the following voltages for each electrode in the Einthoven Triangle: -0.3 mV +0.7 mV +1 mV B. How you can check that your calculation is correct using the Einthoven's Law:Explanation / Answer
Answer:
1.A)
Measuring range of motion:
Each specific joint has a normal range of motion that is expressed in degrees.
Devices to measure range of motion in the joints of the body include the goniometer and inclinometer which use a stationary arm, protractor, fulcrum, and movement arm to measure angle from axis of the joint.
As measurement results will vary by the degree of resistance, two levels of range of motion results are recorded in most cases.Several types of Range of motion exercises are:
Passive range of motion (or PROM) - Therapist or equipment moves the joint through the range of motion with no effort from the patient.
Active assistive range of motion (or AAROM) - Patient uses the muscles surrounding the joint to perform the exercise but requires some help from the therapist or equipment (such as a strap).
Active range of motion (or AROM) - Patient performs the exercise to move the joint without any assistance to the muscles surrounding the joint.
2.A)
Yes it is necessary to recognize the sigals of Electrocardiography (ECG) is the acquisition of electrical activity of the heart captured over time by an external electrode attached to the skin. Each of the cell membrane that form the outer covering of the heart cell have an associated charge which is depolarized during every heart beat. These appear as tiny electrical signals on the skin which can be detected and amplified by the ECG.
3.A)
The rate at which samples are taken by the oscilloscope is called the sample frequency, the number of samples per second. A higher sample frequency corresponds to a shorter interval between the samples. As is visible in the picture below, with a higher sample frequency, the original signal can be reconstructed much better from the measured samples.
The sample frequency must be higher than 2 times the highest frequency in the input signal. This is called the Nyquist frequency. Theoretically it is possible to reconstruct the input signal with more than 2 samples per period. In practice, at least 10 to 20 samples per period are recommended to be able to examine the signal thoroughly in an oscilloscope. When the sample frequency is not high enough, aliasing will occur.
4a.)
The P wave represents the wave of depolarization that spreads from the SA node throughout the atria, and is usually 0.08 to 0.1 seconds (80-100 ms) in duration. The brief isoelectric (zero voltage) period after the P wave represents the time in which the impulse is traveling within the AV node (where the conduction velocity is greatly retarded) and the bundle of His. Atrial rate can be calculated by determining the time interval between P waves. Click here to see how atrial rate is calculated.
4b.)
It is important to remember that the P wave represents the sequential activation of the right and left atria, and it is common to see notched or biphasic P waves of right and left atrial activation.
P duration < 0.12 sec
P amplitude < 2.5 mm
Frontal plane P wave axis: 0 to +75
May see notched P waves in frontal plane
5.A)
The string galvanometer consists of a thin thread conducting the electric
current which is stretched as a string in a magnetic field. The thread, as soon
as the current passes through it, is displaced from its position of equilibrium
in a direction at right angles to the direction of the lines of magnetic force.
The amount of displacement is proportional to the strength of the current
passing through the thread, so that this current can be easily and accurately
measured.
The string galvanometer is within the limits mentioned useful for numerous
purposes. For wireless telegraphy a model has been built which has rendered
very good service as a receiving apparatus. A short string in vacuo is
tuned to the frequency of the ether oscillations which are sent from some
transmitting station. From the ether oscillations high-frequency alternating
currents are obtained by one of the usual methods which one sends through
the accurately tuned string. As soon as a signal is sent the string is set in motion
and its movements are photographed on a moving strip of paper, so
that the dots and dashes can be recorded. Thus one has a recording apparatus
which is very sensitive, and its decrement can be made precisely controllable
and extraordinarily small.
6.A)
Einthoven completed a series of prototypes of a string galvanometer. This device used a very thin filament of conductive wire passing between very strong electromagnets. When a current passed through the filament, the electromagnetic field would cause the string to move. A light shining on the string would cast a shadow on a moving roll of photographic paper, thus forming a continuous curve showing the movement of the string. The original machine required water cooling for the powerful electromagnets, required 5 people to operate it and weighed some 270 kilograms. This device increased the sensitivity of the standard galvanometer so that the electrical activity of the heart could be measured despite the insulation of flesh and bones.
7.A)
Einthoven invents a new galvanometer for producing electrocardiograms using a fine quartz string coated in silver based on ideas by Deprez and d'Arsonval (who used a wire coil). His "string galvanometer" weighs 600 pounds. Einthoven acknowledged the similar system by Ader but later (1909) calculated that his galvanometer was in fact many thousands of times more sensitive.He discusses commercial production of a string galvanometer with Max Edelmann of Munich and Horace Darwin of Cambridge Scientific Instruments Company of London.Einthoven starts transmitting electrocardiograms from the hospital to his laboratory 1.5 km away via telephone cables. On March 22nd the first 'telecardiogram' is recorded from a healthy and vigorous man and the tall R waves are attributed to his cycling from laboratory to hospital for the recording.
8.A)
Common abnormalities:
The following are just a few of the most common abnormalities to be encountered. The list is far from exhaustive.
Atrial flutter:
P waves are well demonstrated in II, III and aVF but are best examined in V1.
Atrial flutter shows clear P waves like the teeth of a saw. There is usually a rapid ventricular rate and a 2:1 atrioventricular (AV) block. The atrial rate is usually around 300 a minute with a ventricular rate around 150.
Atrial fibrillation:
In atrial fibrillation (AF) the pattern is far less obvious. There may be rapid, small undulations, no apparent pattern or a pattern like a worn-out saw, compared to the new saw pattern of flutter. This means that the amplitude is much lower than in flutter.
9.A)
In a conventional 12 lead ECG, ten electrodes are placed on the patient's limbs and on the surface of the chest. The overall magnitude of the heart's electrical potential is then measured from twelve different angles ("leads") and is recorded over a period of time (usually 10 seconds).
In this way, the overall magnitude and direction of the heart's electrical depolarization is captured at each moment throughout the cardiac cycle.
The graph of voltage versus time produced by this noninvasive medical procedure is referred to as an electrocardiogram (abbreviated ECG or EKG).
During each heartbeat, a healthy heart will have an orderly progression of depolarization that starts with pacemaker cells in the sinoatrial node, spreads out through the atrium, passes through the atrioventricular node and then spreads throughout the ventricles.
This orderly pattern of depolarization gives rise to the characteristic ECG tracing. To the trained clinician, an ECG conveys a large amount of information about the structure of the heart and the function of its electrical conduction system.
Among other things, an ECG can be used to measure the rate and rhythm of heartbeats, the size and position of the heart chambers, the presence of any damage to the heart's muscle cells or conduction system, the effects of cardiac drugs, and the function of implanted pacemakers.
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