Explain why it is important that a pulse oximeter can measure both heart rate and blood oxygen level, and describe how changes in these measurements might indicate that a patient's condition is getting worse.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A pulse oximeter is a medical device clipped to a patient's finger. It uses light to monitor two key physiological variables without breaking the skin.
Model answer (5 marks)
A pulse oximeter measures heart rate (pulse rate) and blood oxygen level (SpO₂). These two variables together show how well the heart and lungs are working. If the heart rate rises or becomes irregular (tachycardia) or falls (bradycardia), it signals that the body is under stress and the condition may be worsening. A fall in SpO₂ below the normal range (≈95 %) indicates hypoxia, meaning the patient is not receiving enough oxygen, which also shows a deteriorating state.
Examiner tips
- Use the exact terms ‘heart rate’, ‘pulse rate’, ‘blood oxygen level’, ‘SpO₂’, ‘tachycardia’, ‘bradycardia’, ‘hypoxia’
- Show the link between the two measurements and the heart‑lung system
- Explain both heart‑rate and SpO₂ changes as signs of worsening
Common mistakes
- Confusing SpO₂ with oxygen pressure (PaO₂)
- Lacking the normal SpO₂ threshold (~95 %)
- Only mentioning one variable instead of both
Mark scheme (5 marks)
- A pulse oximeter measures heart rate / pulse rate
- A pulse oximeter measures blood oxygen level / oxygen saturation (SpO₂)
- Together these two measurements give information about how well the heart and lungs / circulatory and respiratory systems are functioning
- A rising or irregular heart rate / tachycardia OR a falling heart rate / bradycardia indicates worsening condition
- A fall in blood oxygen level / oxygen saturation below normal (below ~95%) indicates the patient is not receiving enough oxygen / hypoxia / worsening condition
Key terms in this question
pulse oximeter · heart rate · blood oxygen level
Related
- All AQA A-Level Physics (7408) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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