Compare ECG pulse and heart-sound monitoring
Describe three monitoring methods without treating their signals as identical.
Section B9.2 · Heart
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Recall pressure-producing ventricular contraction and valve action.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does an ECG record?
What you will learn
- Electrical activity and an arterial pressure wave
- Heart sounds are associated with valves closing
Electrical activity and an arterial pressure wave
An electrocardiogram, or ECG, records the heart’s electrical activity using electrodes. Repeating features can be used to determine heart rate. The trace records electrical signals; it is not a direct picture of the amount of blood in a ventricle. You do not need clinical trace diagnosis for this objective.
Pulse rate can be counted at a suitable artery, such as the wrist. Each pulse is the pressure wave associated with ventricular pumping. For a regular count in a teaching investigation, 18 pulses in 15 seconds gives 18 × 4 = 72 beats per minute. A short sample is more sensitive to counting error and changing rate.
Heart sounds are associated with valves closing
Listening with a stethoscope detects heart sounds associated with closure of the valves. The first and second main sounds reflect closure events at different points in a cardiac cycle. Two sounds are not two separate complete heartbeats.
These methods monitor different signals: electrical activity, an arterial pressure wave and audible valve closure. Measurements can be compared, but a school exercise cannot diagnose a learner’s heart health from a single count or trace. Use supplied records or an appropriate supervised activity; do not perform clinical interpretation.
Sources for this lesson
Pause and explain
A regular sample has 18 pulses in 15 seconds. What is the estimated rate?
Worked example
A regular teaching record contains 18 pulses in 15 seconds. Calculate the estimated rate.
Show the worked solution
- Scale the observation to 60 seconds: 60 ÷ 15 = 4.
- 18 × 4 = 72.
Answer 72 beats per minute, based on the supplied regular short sample.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Match ECG, wrist pulse and stethoscope listening to electrical activity, pressure wave and valve-closing sounds.
Give me a hint
Keep the recorded signal distinct from the instrument.
Compare my reasoning
- ECG records electrical activity.
- Pulse detects a pressure wave; listening detects sounds.
ECG → electrical activity; pulse → arterial pressure wave; listening → sounds associated with valve closure.
Look for these in your work
- Correct three matches
- Do not equate all signals
A regular record shows 22 pulses in 20 seconds. Calculate beats per minute.
Give me a hint
Multiply by 60 ÷ 20.
Compare my reasoning
- 60 ÷ 20 = 3.
- 22 × 3 = 66.
66 beats per minute.
Look for these in your work
- Correct scaling
- Include the rate unit
A recording has 30 complete lub-dub pairs in 30 seconds. Why is 120 beats per minute wrong?
Give me a hint
One complete pair belongs to one cycle.
Compare my reasoning
- Count 30 pairs as 30 cycles, not 60 separate beats.
- 30 cycles in 30 seconds scales to 60 per minute.
60 beats per minute; 120 incorrectly counts each of the two main sounds as a whole heartbeat.
Look for these in your work
- Count complete cycles
- Explain the doubled-count error
Common mistakes
- Counting two valve sounds as two heartbeats.
- Calling an ECG a direct blood-flow measurement.
What can you explain now?
A regular sample has 18 pulses in 15 seconds. What is the estimated rate?
Compare with the explanation
72 beats per minute
18 × (60 ÷ 15) = 72.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Describe what each monitoring method actually detects before calculating any rate.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.