Deep breathing also goes by the names of diaphragmatic breathing, abdominal breathing, belly breathing, and paced respiration. When you breathe deeply, the air coming in through your nose fully fills your lungs, and the lower belly rises.
For many of us, deep breathing seems unnatural. There are several reasons for this. For one, body image has a negative impact on respiration in our culture. A flat stomach is considered attractive, so women (and men) tend to hold in their stomach muscles. This interferes with deep breathing and gradually makes shallow "chest breathing" seem normal, which increases tension and anxiety.
Shallow breathing limits the diaphragm's range of motion. The lowest part of the lungs doesn't get a full share of oxygenated air. That can make you feel short of breath and anxious. Deep abdominal breathing encourages full oxygen exchange — that is, the beneficial trade of incoming oxygen for outgoing carbon dioxide. Not surprisingly, it can slow the heartbeat and lower or stabilize blood pressure.