Pupils of all ages are keenly interested in how physical and mental stress affects their heart rate. The sensing clip (pleth) can be attached to a finger or ear lobe to measure either blood flow (pulse waveform) or heart rate (beats per minute).

It works best if the test subject keeps the finger with the sensing clip absolutely still.

Note: To monitor strenuous activity, see the Polar Heart Rate sensor (3148).

Applications

Biology:

• Heart rate changes due to activity
• Recovery rate
• Pulse rate
• Effect of food (chocolate) or mild stimulants (caffeine)
• Effect of music on pulse rate
• The effect of the strictest teacher entering the room!

The Heart Rate sensor clip (pleth) holds an infrared LED that shines a light through either the finger or ear lobe and a light sensitive detector. As the amount of light transmitted varies with the flow of blood, the sensor can record either the pulse waveform, or beats per minute. The sensor uses averaging techniques to ensure a smoother reading.

In use, the red LED on the sensor housing will flash in time with the heartbeat. Wait for this signal to stabilise before starting a recording.

Note: Some subjects may have poor peripheral circulation (the extent to which the blood vessels in the fingertip are filled with blood), in which case another subject should be selected. Some subjects may need to rub their hands together to increase the blood flow. Values should not be affected by skin colouring.