You can also practice pursed lip breathing. This is a technique used by many individuals who have compromised breathing to help them get more air out of their lungs. This will help to expel any gas trapped in your lungs theoretically, and also creates a habit you can adopt when you are feeling breathless. You can sit down with your back straight and relax your shoulders for this exercise. Take a deep breath in through your nose (1-2 seconds), and purse your lips like you are blowing hot food and breathe out slowly. Try to increase the counts of exhalation to make it harder.