Thats an incentive spirometer. It’s meant to encourage patients bedridden to fill the lungs fully with air periodically to prevent atelectasis (incomplete expansion of lungs)
There is a better and safer way to fill the lungs with air.
Triple stacked breathing:
1. Sit up straight to free the rib cage.
2. Take three consecutive inspirations (breathing in) stacked upon the each previous one without expiration (breathing out).
3. Hold the fully filled lung for a few second and then let it all flow out.
4. Repeat sets of 3 every hour.
It is not necessary once physical activity is restored.
My challenge with incentive spirometer is that it encourages rapid inspiration which can cause unnecessary aspiration of oral bacteria flora into the lungs and increase risk of hospital acquired pneumonia. The goal is the fill the lungs fully; speed does not matter. So try triple stacked breathing instead.