A couple of weeks back we did a straw breathing session in class. Students counted the number of breaths they took whilst I timed them for a minute.
They then breathed in through the nostrils and out through a straw for several minutes, first making sure that the straw was not providing too much resistance for them to exhale comfortably. If it was we either cut the straw in half or else they dispensed with the straw altogether and breathed out through pursed lips as if about to whistle.
Then, having finished with the straw, they counted the breath breathing normally whilst I timed them for a minute, as before. Students can get anything from no change (quite rare) to really quite significant drops (e.g. 20%, 50%, 66%) in the number of breaths they take between the before and after breathing counts.
This week a student told me that she had since tried this out with her adult nephew who has quite severe asthma. He was amazed when the number of breaths he took in a minute dropped from 27 to 11!