How deep can you breathe on a spirometer?

Your lung capacity is mostly a function of your height. The predicted value is based on your age, height, weight, gender, and ethnic background. Your height has the most significant impact followed by gender then ethnicity. Taller people have a larger lung capacity than shorter people. Keeping all other things equal, men have a larger capacity than women (by about 12%). Heavier people have a smaller capacity than slender people of the same height, ethnicity, etc.

Those numbers are milliliters. Depending on your height and gender we would expect you to be able to move between 2-4L (2000-4000mL). The vast majority of people have a lung capacity under 4L. Some people are going to be on the low end of the scale; some on the high end. I'm quite tall and my normal vital capacity is around 6L. My mom is quite short and I would not expect her to be able to do much more than 1.5L at her very best. I have no trouble at all pegging the largest incentive spirometer all the way to the top with little effort. Other people will never get that anywhere near the top no matter how hard they try.

For post-op pneumonia and atelectasis prevention, we want you to be able to eventually achieve 85% of your pre-op predicted value. If you could do 4L before surgery we want to see you hit around 3500 after surgery. You'll almost certainly be well below that to start. So we watch you do it, measure how much you can do, and observe the trend over a few days. We expect it to start at about half of your pre-op value. If after a couple of days it hasn't increased or it goes down, we need to do something more -- you're on your way to a pneumonia.

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