https://www.ahajournals.org/doi/10.1161/JAHA.121.020980
It seems that using one of these…
https://smile.amazon.co.uk/gp/product/B007CI0ZBC/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
…set to about 70% of your maximum inspiratory effort (100% being just unable in inhale) for 30...