Read the passage and answer the following questions : Engineering measurement techniques have made substantial contributions in the accurate determinations of various physiological parameters, that give useful information to clinicians to detect the mal-functioning of the system being measured and also aid in proper diagnosis and patient care. Some of the biomedical instruments may be designed and developed for a particular specialised requirement but a majority of them are adaptations of widely used physical measuring devices. For monitoring the temperature of biomedical subjects, a thermister device is generally used along with a suitable bridge circuit in which the terminal device may be a voltmeter, calibrated in terms of degrees Celsius or Fahrenheit.
The amplitude of an electrocardiograph signal is usually of the order of
1 mV
The standard figure. A surface ECG recorded from skin electrodes has a peak amplitude of about 1 mV — the R wave of the QRS complex typically reaching 1–2 mV, with the P and T waves only a few tenths of a millivolt. The usual quoted range for the whole signal is 0.5 to 4 mV.
Why the other values are wrong by orders of magnitude. 0.001 mV (1 μV) is a thousand times too small — that is the level of an EEG component or of amplifier noise, not of a cardiac signal. 10 mV and 20 mV are ten and twenty times too large; potentials that big appear only on electrodes placed directly on the heart during surgery.
Comparison with the other biopotentials is the useful thing to remember, since they span three decades:
| Signal | Typical amplitude | Bandwidth |
|---|---|---|
| ECG (heart) | 1–2 mV | 0.05–100 Hz |
| EMG (muscle) | 0.1–5 mV | 10–2000 Hz |
| EEG (brain) | 10–100 μV | 0.5–100 Hz |
| ERG (retina) | 0.5 mV or less | 0.2–200 Hz |
What the small size demands of the electronics. A millivolt signal must be amplified by roughly a thousand times to reach a usable level, and it arrives riding on mains interference and electrode half-cell potentials that can be hundreds of times larger. The front end is therefore a differential instrumentation amplifier with CMRR of 100 dB or more, high input impedance, and isolation for patient safety — exactly the adaptation of standard measuring technique that the passage describes.
Hence, the amplitude of an electrocardiograph signal is of the order of 1 mV.
Similar Questions
Read the following statements regarding errors in measurement :
(a) Gross errors are mostly due to lack of knowledge and care on the part of the experimenter.
(b) Systematic errors are mostly caused by inherent short-comings of the instruments and components used in measurement.
(c) Random errors are due to sources and causes that cannot be specified for their effects with.
(d) Gross and systematic errors are non-correctable.
Which of the above are correct ?
Blood pressure is measured by
Assertion (A) : In a well-type manometer, ratio of cross-sectional areas of well and the tube is not the factor that determines the scale of the manometer.
Reason (R) : Accuracy of a manometer is not affected by the shape or size of the tubes.
Electrocardiogram is a graphical representation of electrical activity of heart muscle myocardium, in the form of
For the quantitative measurement of acidity or alkalinity, the instrument used is
In the bio-electric phenomenon, ERG is used to detect
An ammeter of 1 mA possesses a resistance of 100 ohms. This ammeter is to be converted into 1A ammeter. The value of shunt resistance required will be :
Followings is the sequence of blocks in spectrum Analyser :
A. Detector & video Amplifier
B. Fixed Frequency Active filter
C. Attenuator (Adjustable)
D. Mixer & Tunable Detector
Choose the correct answer from the options given below :
Read the following statements regarding biomedical instrumentations :
(a) Sphygmos is used for blood pressure measurement.
(b) EMG represents a record of the electrical activity of the brain.
(c) ERG represents the record of potential from the retina.
(d) ECG represents the record of electrical activity of brain.
Which of the above statements are correct ?
Optical pyrometers are used to measure :
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Which of the following is NOT a cause of food and water contamination?
