“Breathing out requires no effort from your body unless you have a lung disease or are doing physical activity. As your lungs expand, air is sucked in through your nose or mouth. The air travels down your windpipe and into your lungs. After passing through your bronchial tubes, the air finally reaches and enters the alveoli (air sacs) but with COPD this is not the case.”
NIH National Heart, Lung, and Blood Institute.