# 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.

> AQA A-Level Physics (7408) — 3.10.3 Biological Measurement · Explain · 5 marks

> 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.

## Mark scheme (5 marks)

1. A pulse oximeter measures heart rate / pulse rate
2. A pulse oximeter measures blood oxygen level / oxygen saturation (SpO₂)
3. Together these two measurements give information about how well the heart and lungs / circulatory and respiratory systems are functioning
4. A rising or irregular heart rate / tachycardia OR a falling heart rate / bradycardia indicates worsening condition
5. 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

- [pulse oximeter](https://www.gradenine.co.uk/glossary/pulse-oximeter)
- [heart rate](https://www.gradenine.co.uk/glossary/heart-rate)
- [blood oxygen level](https://www.gradenine.co.uk/glossary/blood-oxygen-level)

## Related

- [Revision notes for AQA A-Level Physics (7408)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-it-is-important-that-9983268c) · Published by Druglandscape Ltd.