Biological Measurement (AQA A Level Physics): Flashcards
Exam code: 7408
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- FrontECG Machines
Define electrocardiogram (ECG).
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Define electrocardiogram (ECG).
A graph of the potential difference between electrodes (in mV) against time (in s), used to monitor the electrical activity of the heart.
Where are ECG electrodes placed to obtain the largest potential difference?
In six standard positions on the chest, plus one on each limb (close to the arteries).
State two ways of ensuring good electrical contact between ECG electrodes and the patient.
Any two from:
Remove hairs and dead skin cells before attaching the electrodes
Coat the electrodes with a conductive gel
Use electrodes made from a non-reactive material
What three properties should the amplifier in an ECG machine have?
High gain, low noise and high input impedance.
The P wave of an ECG corresponds to the .......... of the atria.
The P wave of an ECG corresponds to the contraction (depolarisation) of the atria.
What physical event does the QRS wave correspond to, and when does it occur relative to the P wave?
The contraction (depolarisation) of the ventricles; it occurs 0.2 s after the P wave.
What physical event does the T wave correspond to?
The relaxation (repolarisation) of the ventricles, occurring 0.2 s after the QRS wave.
True or False?
The QRS wave has a smaller amplitude on the ECG trace than the P wave.
False.
The QRS wave signal is much greater than the P wave, reaching a maximum of about 1 mV.
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