ECG Instrumentation

Question 1

What is an electrocardiograph?

Answer 1

instrument for recording the electrical activity of the heart

Question 2

What is the role of an electrocardiogram?

Answer 2

produces tracing of the electrical activity of the heart

Question 3

what are the units of current?

Answer 3

Amps (I)

Question 4

what are the units of potential difference?

Answer 4

volts (V)

Question 5

What are the unit of resisitance?

Answer 5

ohms

Question 6

What is a biopotential system?

Answer 6

system that measues something biological

Question 7

What are the 3 core componenets that make up the biopotential system?

Answer 7

-tranducer
-processor
-display

Question 8

What is the role of a transducer?

Answer 8

converts one form of energy to another

Question 9

What is the role of a producer?

Answer 9

proccesses the signal
-amplify

Question 10

whats the role of a display?

Answer 10

to show the digitilised results of a test eg- ecg, temperature

Question 11

Whats the aim of a biopotential signal?

Answer 11

to get a signal from input to output without changing it

Question 12

What are the measurements of ECGs?

Answer 12

-amplitude (voltage)
-Time

Question 13

What is an ECG in regards to measurements?

Answer 13

a voltage time graph

Question 14

Name some equiptment specific requirements

Answer 14

-input impedance
-common mode
-rejection ratio
-linearity
-time constant
-patient isolation

Question 15

Name some operator adjustable features of an ECG

Answer 15

-sensitivity
-paper speed
-frequency response

Question 16

What is input impedance?

Answer 16

a measure of the impedance to current flow offered by an electrocardiograph

Question 17

What is ohms law?

Answer 17

V=IR

the voltage across a conductor is directly proportional to the current flowing through it

Question 18

What is the equation for total resistance?

Answer 18

R total =R1 +R2 +R3 (series)

Question 19

What does AHA state about input impendence?

Answer 19

input impendance should be greater than 0.5 M ohms

Question 20

Describe the common mode rejection ratio

Answer 20

A measure of how well the machine is detecting noise

-electrodes pick up noise including common mode voltage

-the ability of the ECG amplifier to reduce common mode voltage noise

Question 21

What does the AHA say the CMRR should be ?

Answer 21

1000:1
between 45-65 Hz when imbalanced at 5K ohms

Question 22

What does AHA state about linearity?

Answer 22

maximum error must be less than 5% of the chart width

Question 23

What happens if the linearity is not met?

Answer 23

-ECG waveforms will be distorted
-ECG should be as linear as possible
-Cant change it

Question 24

What is the time constant?

Answer 24

the ability of the ECG system to process low frequency or slowly changing signals

-Time taken for the amplitude of a step change voltage to decay to 36.8% of its initial value

Question 25

What does AHA state about time constant?

Answer 25

must be greater than 3.2 seconds

Question 26

What happens if the time constant is incorrect?

Answer 26

-low frequency parts of an ECG waveform will be distorted
-time constant should be long enough to display an undistorted T wave

Question 27

Define patient isolation

Answer 27

the maximum amount of current that the system can pass to the patient

Question 28

What does AHA state that patient isolation should be?

Answer 28

less than 10 microamps

Question 29

What are the effects of patient isolation if its incorrect?

Answer 29

depends on the frequency and current but can vary from mild sesation to burns, ventricular fibrilation

Question 30

What are some dangerous patient isolation values?

Answer 30

0.9-1.2mA – current perceptible​

15-20mA – muscle contraction (unable to release grip)​

50-100mA – ventricular fibrillation (death)​

100-200mA – severe burns, constriction of muscle groups​

Question 31

How do you check the patient isolation is correct?

Answer 31

Check the Electrocardiograph has had an electrical safety test. Visually inspect the system before use.​

Question 32

What is sensitivity?

Answer 32

The sensitivity of the ECG may be altered to increase or decrease the amplitude of the ECG on the trace​
Common choices are​

5 mm/mV​

10 mm/mV​

20 mm/mV​

Question 33

What does AHA state sensitivity should be?

Answer 33

1mV must equal 10mm on the paper​

Question 34

What are the effects if sensitivity is not met?

Answer 34

The ECG waveform amplitude will be reduced or increased in size. ​
Possible misdiagnosis.

Question 35

What does sensitivity effect?

Answer 35

waveform size

Question 36

What should I do to check the sensitivity of the ECG?

Answer 36

Use a sensitivity of 10mm/mV​

Check machine setting before you start​

Use alternative in exceptional circumstances ​

Clearly annotate ECG trace​

Additional ECG on 10mm/mV​

Question 37

Whats the effect if paper speed is not met?

Answer 37

The ECG waveform will be reduced or increase in duration​

Heart rate will appear higher or lower​

Question 38

How should I check ECG paper speed?

Answer 38

Paper speed affects the timing of the waveform​

Use 25 mm per second​

Check the setting before you start​

Use an alternative in exceptional circumstances​

Annotate trace​

Use 25mm/s as well (record both)​

Question 39

What is frequency response?

Answer 39

the range of frequencies over which the ECG works

Question 40

What does AHA state about frequency response?

Answer 40

equal to 0.05 to 150 Hz

Question 41

What happens if frequency response is not met?

Answer 41

waveform is distorted

Question 42

What should I do to check frequency response?

Answer 42

switch the mains (50 Hz) filter on ONLY once all noise sources have been excluded​

Clearly annotate ‘Filter on’​

-effects waveform shape