ECG/BP Instrumentation

Question 1

What do electrodes do?

Answer 1

Transducers which measure the ionic potential difference between their respective points of application on the body surface.

Question 2

What are silver-silver chloride electrodes?

Answer 2

• Metal is silver, salt is silver chloride, electrode jelly between silver and skin, forms a local
  solution, silver ions formed.

Question 3

What are wet gel electrodes?

Answer 3

• Water (allows gel to penetrate skin)
• salt (electrical connection between patient/electrode)
• thickening agent (viscosity for application)
• bactericide (prevent bacterial growth)

Question 4

What are solid/hydro gel electrodes?

Answer 4

• Wet gel
• no adhesive properties
• synthetic polymer (maintains structure of gel),
• salt (electrical activity)
• water (dissolve salts/gel).

Question 5

What are ECG recordings dependent on?

Answer 5

• Good skin preparation,
• quality electrodes
• continuous electrical pathway from skin to ECG
  machine

Question 6

What is the sampling rate of ECG?

Answer 6

• Speed = 25mm/s.
• Sampling rate = 4kHz
• Frequency response = 0.05 – 100Hz.

Question 7

Define differential amplifier

Answer 7

Differential = type of electronic amplifier that amplifies the difference between two voltages

Question 8

Define buffer amplifier

Answer 8

• Buffer = high input impedance to signal being picked up by active electrodes, ECG machine will record the correct potential from the heart, increases SNR.

Question 9

What is the driven right leg feedback loop?

Answer 9

• Right leg electrode records the noise signal,
• noise signal is inverted at the amplifier output
• noise signal is subtracted from the noise signal from the other electrodes
• it is cancelled out before input to differential amplifier.

Question 10

What is ECG sensitivity?

Answer 10

• 10mm/mV, 5mm/mV (large amplitude QRS in hypertrophy)
• 0mm/mV (low amplitude
  complexes in obesity).

Question 11

What is a pressure wave?

Answer 11

• Complex periodic fluctuation in force/area

- consists of heart rate/harmonics

Question 12

What are the four measures of blood pressure?

Answer 12

• Systolic = pressure in arteries when the heart is beating.
• Diastolic = pressure in arteries when the heart is not beating.
• Pulse = difference between systolic and diastolic pressures.
• Mean arterial pressure = average arterial pressure over a cardiac cycle.
• Pulse Transit Time and Pulse Wave Velocity = time/speed of blood.