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.
Electrocardiogram is a graphical representation of electrical activity of heart muscle myocardium, in the form of
A time varying voltage
What an ECG actually records. Heart muscle cells depolarise and repolarise as they contract, and those ionic movements set up small potential differences that spread through the body's tissues. Electrodes placed on the skin pick up the resulting potential difference, so the trace is a plot of voltage against time.
Why it must be a voltage. The body is a volume conductor, and the recording instrument is deliberately given a very high input impedance so that it draws essentially no current from the patient — both for safety and to avoid loading the source. What is being sensed is therefore the potential difference between electrode sites, not a current; a time-varying current (option 2) would require the instrument to complete a low-impedance path through the body, which is exactly what biomedical amplifiers are designed to avoid.
The familiar waveform is read as a sequence of voltage deflections:
| Feature | Represents |
|---|---|
| P wave | atrial depolarisation |
| QRS complex | ventricular depolarisation |
| T wave | ventricular repolarisation |
Ruling out the other two. A time-varying pressure is what a sphygmomanometer or a catheter transducer records — that is the mechanical consequence of the beat, not its electrical activity. A time-varying blood concentration belongs to chemical measurements such as blood-gas or dye-dilution analysis. The question's own wording, "electrical activity", already points to the electrical quantity.
What this demands of the instrument. The signal is only about a millivolt and lies in the 0.05–100 Hz band, sitting on far larger common-mode interference from the mains. That is why an ECG front end is a high-CMRR instrumentation amplifier with a right-leg drive — a direct illustration of the passage's point that physiological measurement borrows and adapts standard electronic techniques.
Hence, an electrocardiogram is a record of a time varying voltage.
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.
For the quantitative measurement of acidity or alkalinity, the instrument used is
The amplitude of an electrocardiograph signal is usually of the order of
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 :
Important Questions from Miscellaneous
The ration of the number of girls and boys in a school is 8 : 7. If the percentage increase in the number of girls and boys is 10% and 20% respectively, what will be the new ratio?
The cheapest means of transport is:
The property of Catenation is most readily predominant in:
Which newspaper edited by Bal Gangadhar Tilak, was one of the strongest critics of the British rule?
Which of the following is NOT a cause of food and water contamination?
