I am trying to make DIY Bubble CPAP that can put a constant pressure on patient. I am using an Aquarium Oxygen pump as air source. The motor says 38L/Min in the spec. And by googling I found that an average adult can takes up to 7L/min air while resting. But when I used it, I felt like I am getting very low air flow.

Can anyone help, what am I missing?

Incase you there is any suggestion please drop it too. Thank you.

  • 1
    $\begingroup$ 7l/min? That seems low, perhaps 4 to 7 litres per breath and then how many breaths per minute? $\endgroup$
    – Solar Mike
    Commented Apr 23, 2020 at 14:28
  • $\begingroup$ Yeah, Wikipedia has average adult lung capacity at around 6 liters, so Solar Mike's comment is probably correct. $\endgroup$
    – Wasabi
    Commented Apr 23, 2020 at 14:30
  • $\begingroup$ I think I made a mistake. The link below says 7-8 Litres of Oxygen But it's not just pure Oxygen. There are other airs too. sharecare.com/health/air-quality/oxygen-person-consume-a-day $\endgroup$ Commented Apr 23, 2020 at 16:23
  • $\begingroup$ It would be an idea to make sure you get this right before you kill yourself or someone else. $\endgroup$
    – Solar Mike
    Commented Apr 23, 2020 at 17:49
  • $\begingroup$ I held the mask with hand. So when the airflow was low, I could easily remove the mask and breathe. $\endgroup$ Commented Apr 23, 2020 at 17:57

1 Answer 1


A medical device known as an incentive inspirometer measures volume of air inhaled. Twenty years ago, I could pull five liters (was serious cyclist) but now I'm down to four liters per breath. Sixteen breaths per minute means sixty-four liters per minute.

At the five liter value, that's eighty liters per minute, in resting state.

incentive inspirometer image

  • $\begingroup$ I did an exercise with students to show how much air they used per minute and compared the total to the volume of air in the room - explaining the reasons for ventilation in rooms & buildings. Used party balloons - they had to blow them up with 4 breaths, then we approximated the volume from the diameter and divided by four... A fun exercise. $\endgroup$
    – Solar Mike
    Commented Apr 23, 2020 at 15:57
  • $\begingroup$ Thank you, I think I am heading in the right direction. The source where I found 7L/min was actually total Oxygen per minute. So the total air in litre will be much more. Which is around 80L/Min the amount you mentioned. Thank you $\endgroup$ Commented Apr 23, 2020 at 16:27

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