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Calculating the Heart Rate With a Pulse Plethysmograph Results


Figures 4 and 5 below shows traces that were obtained using the pulse plethysmograph.
As described in the experiment, using these traces it is possible to calculate the beat–by–beat (instantaneous) heart rate.

Heart rate trace — 51½ beats per minute

Figure 4: Heart rate trace — 51½ beats per minute

Pulse Plethysmograph results during deep breathing

Figure 5: Pulse Plethysmograph results during deep breathing

Teachers’ notes

Safety issues:


Target age groups:

Ages 7–18 (Key Stage levels 2 and 5)

National curriculum:

In this activity the pulse rate is measured via an infrared led and phototransistor detecting, by the absorption/reflection of the IR radiation, the change of blood volume in the tissues produced following each heart beat. Whilst relating directly to KS2 Sc2 Life processes and living things, Humans and other animals, Circulation 2c/d, it would also be of interest to those studying the many medical physics and electronic instrumentation modules at AS/A/AVCE levels. Whilst at KS2 one would not expect the pupils to calculate the pulse rate from the Pico screen display, their seeing the effect on the pulse display of a higher/lower pulse rate would be useful.