How Do You Measure a Pulse/Heart Rate?

Place two fingertips over the radial artery at the wrist or the carotid artery in the neck, count the pulses for a measured time, and convert the result to beats per minute. This method is required at both SL and HL in IB Biology subtopic B3.2 Transport.

Measuring the Pulse

A pulse is the pressure wave produced in an artery when the ventricles contract and eject blood. Each detectable pulse normally corresponds to one heartbeat, so pulse rate can be used to estimate heart rate.

1. Ensure the person is resting if measuring resting heart rate.
2. Place the pads of the index and middle fingers over the artery. Do not use the thumb because its own pulse may be detected.
3. Press gently until the pulse can be felt. When using the carotid artery, measure on only one side of the neck.
4. Use a stopwatch to count the pulses for a known interval.
5. Calculate the rate in beats per minute using:

$\text{heart rate} = \dfrac{\text{number of pulses}}{\text{time in seconds}} \times 60$

For example, if 18 pulses are counted in 15 seconds:

$\dfrac{18}{15} \times 60 = 72\text{ beats min}^{-1}$

The procedure can be repeated and a mean calculated to reduce random error. Digital heart-rate monitors can also be compared with manual measurements, but the same unit, $\text{beats min}^{-1}$, should be reported.

Exam Technique

For a calculate question, show the time conversion and include the unit. For a practical-method question, identify the artery, state the counting interval, explain the conversion to one minute, and mention repeats. A common misconception is that the pulse is blood moving through the artery; it is specifically a pressure wave caused by ventricular contraction.