This set of Biomedical Instrumentation Multiple Choice Questions & Answers (MCQs) focuses on “Electrodes for ECG”.
1. The material used in limb surface electrode is ___________
a) German silver
Explanation: The most common type of electrode most routinely used for recording ECG are rectangular or circular surface limb electrodes. The material used in them is German silver, nickel silver or nickel plated steel. They are applied to the surface of the body with electrode jelly.
2. Welsh cup electrodes have __________
a) low contact impedance
b) negligible contact impedance
c) high contact impedance
d) zero contact impedance
Explanation: Welsh cup electrodes or suction electrodes is a metallic cup shaped electrode which is used for recording ECG from various positions from the chest. It has a high contact impedance as only the rim of the electrode is in contact with the skin. It is commonly used to record the unipolar chest leads.
3. In floating electrodes metal electrode does not make direct contact with the skin.
Explanation: In floating electrode the metal electrode does not make direct contact with the skin. The electrode consists of a light weighted metalled screen or plate held away from the subject by a flat washer which is connected to the skin. Floating electrodes can be recharged, i.e. the jelly in the electrodes can be replenished if desired.
4. The main design feature of pregelled disposable electrodes which helps to reduce the possibility of artefacts, drift and baseline wandering is _____________
a) low absorbency buffer layer with isotonic electrolyte
b) high absorbency buffer layer with isotonic electrolyte
c) high absorbency buffer layer without isotonic electrolyte
d) low absorbency buffer layer without isotonic electrolyte
Explanation: The main design feature of pregelled disposable electrode that helps in reducing the possibility of artefacts, drift and baseline wandering is the provision of high absorbency buffer layers with isotonic electrolyte. This layer absorbs the effects of movement of the electrode in relationship to the skin and attempts to maintain the polarization associated with the half-cell potential constant.
5. Recording electrical activities associated with heart is known as ____________
Explanation: The recording of the electrical activities associated with the functioning of the heart is known as electrocardiogram. ECG is a quasi-periodical, rhythmically repeating signals synchronized by the function of the heart, which acts as a generator of bioelectric events. This generated signals can be described by the means of a simple electric dipole.
6. Which of the following is considered to be the primary pacemaker of the heart?
a) sino-atrial node
b) atrio-ventricular node
c) purkinje fibres
d) bundle of his
Explanation: Located in the top right atrium near the entry of the vena cava, are a group of cells known as the sino-atrial node (SA node) that initiates the heart activity. Because this is also considered as the primary pacemaker of the heart. The SA node is 25 to 30 mm in length and 2 to 5 mm in thickness.
7. Atrio ventricular node is located at __________
a) upper part of the heart wall between the two atrial
b) lower part of the heart wall above the two atrial
c) lower part of the heart wall between the two atrial
d) upper part of the heart wall above the two atrial
Explanation: The AV node is located in the lower part of the wall between the two atria. The AV node delays the spread of excitation for about 0.12s, due to the presence of a fibrous barrier of non-excitable cells that effectively prevent its propagation from continuing beyond the limits of stria.
8. Buffer amplifier converts ____________
a) low impedance signals to high impedance signals
b) high impedance signals to low impedance signals
c) ac impedance signals to dc impedance signals
d) dc impedance signals to ac impedance signals
Explanation: Noise is typically generated from motion artefacts and power line interference. A common solution used to suppress noise in dry electrode signals is a buffer amplifier. A buffer amplifies is essentially an impedance converter, that converts high impedance signals to low impedance signals.
9. Which of the following is a wireless ECG acquiring system?
a) pregelled disposable electrodes
b) limb electrodes
c) pasteless electrodes
d) smart pad
Explanation: Smart pad is a system that displays patients electrocardiogram signals without adhesive pads, wires or active intervention from a clinician. The system automatically selects three electrodes from an array of Cu/Ni fabric based electrodes patterned on a thin pad on which the patient lies. The selected electrodes are used to provide a differential 3 lead measurement of the patient’s ECG, which is then transmitted wirelessly and displayed on a laptop computer.
10. Before placing the electrodes the skin should be __________
Explanation: The skin should be dry. Poor skin prep prompts undesirable curio and not putting the terminals where they ought to be can change the morphology (shape) of the waveforms the specialist will decipher. The purpose of decent skin prep is to expel soil, dead skin cells, oils, skin cream, counterfeit tan, body powder, sweat and so forth. These sources can prompt poor contact with the sensors and ancient rarity.
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