Maths Skill: PVR
- The volume of air within the lungs of an individual will change depending on their level of activity
- When at rest, breathing is shallow and steady
- When exercising, breathing is deeper and more frequent
- The volume of air inspired per breath when at rest is the tidal volume
- The breathing rate is the number of breaths taken per minute
- Using the results from a spirometer a trace can be created to show the volume changes in the lungs
The changes in the volume of air present in the lungs are shown here. Note the residual volume, this is the volume of air left in the lungs after as much air has been breathed out as possible.
Calculating the Pulmonary Ventilation Rate
- The volume of air breathed (in OR out) in one minute is known as the pulmonary ventilation rate
- It is calculated by multiplying the tidal volume by the breathing rate
PVR = tidal volume x breathing rate
Worked example
An individual's pulmonary ventilation rate at rest was found to be 7.4 dm3 min-1. They took 12 breaths in one minute. Calculate their tidal volume.
Step One: Rearrange the equation
PVR = tidal volume x breathing rate
Rearange to:
Tidal volume = PVR ÷ breathing rate
Step Two: Insert relevant figures
Tidal volume = 7.4 ÷ 12 = 0.6166
Tidal volume = 0.62 dm3
Examiner Tip
You don’t need to memorise the terms tidal volume, vital capacity or total lung capacity.
