[header] How to circular breathe [title] Fill your cheeks with air, and breathe in and out through your nose. [step] What you're doing is establishing a second source of air that you can use when your lungs run out. [substeps] While this may make you look like a chipmunk, the more useful analogy is to think of yourself as a human bagpipe, and your cheeks as the bellows. 
[title] Blow out the air you have been holding in your mouth. [step] Close your jaw, but make a tiny opening in your mouth, and use your cheek muscles to push the air out slowly.