I don't know that you actually get more 02, but learning and actually doing diaphragmatic breathing allows you to do a better job of gas exchange. With COPD, we tend to breathe with the chest muscles and not with the diaphragm. That means the diaphragm gets weak and can't work as well. By learning how to breathe using the diaphragm, we actually strengthen the diaphragm and increase its efficiency and the efficiency of our lungs. Here's a link to a site that will give you good instructions on how to learn diaphragmatic breathing: https://www.health.harvard.edu/healthbeat/learn...
The more you practice, the better you'll get at the technique and the stronger your diaphragm will get.
Besides learning how to breathe this way, you should also learn Pursed Lip Breathing. There are lots of sites on the internet that will teach you how to do it. I recommend practicing both these techniques until they're second nattier to you. You will find that your breathing will be easier and you probably won't get short of breath as quickly.

@ jean,,,, you need a new link, that ones gone 404, maybe thats why person above asked for one.,,, maybe

Going to try that Thank you!

I breathe in filling my sides and then abdomen
I breathe out flattening the abdomen and sides. Oxygen levels go up fairly quickly for me doing this.

https://www.health.harvard.edu/healthbeat/learn... same one I posted above.....