Lessons · Medicine foundations · minute ventilation
Minute ventilation: one breath, times the breaths in a minute
Minute ventilation is the tidal volume, the air moved in a single breath, multiplied by the respiratory rate.
Hone is a place to practise a career, one idea a day. This is one of its lessons, written out in full and free to read without an account.
What it is for
In a respiratory practical the two numbers are on the screen in front of you and the question is what they come to together. It is the same shape as cardiac output, which is worth noticing out loud: a volume per event, times events per minute, gives a volume per minute.
How to think about it
Multiply. Then look at the unit: millilitres times breaths per minute is millilitres per minute, and dividing by 1000 makes it litres per minute, which is how it is usually quoted. Nothing is subtracted here; the subtraction comes in the next lesson.
Worked example
Minute ventilation = tidal volume × respiratory rateThe formula.
Tidal volume 500 mL, rate 12 breaths per minuteThe two figures.
500 × 12 = 6000 mL/minMillilitres a minute.
6000 / 1000 = 6.0 L/minSix litres a minute, which is the form said aloud.
Your turn
Tidal volume is 450 mL and the rate is 16 breaths per minute. Write the line that gives the minute ventilation in millilitres per minute.
450 × 16 = mL/min
Solve one, graded on the server
The trap
Halving the answer because air goes in and comes out again. Tidal volume is already the volume of one breath in; the round trip is not counted twice.