There is permanent enlargement of the alveoli due to the destruction of the walls between alveoli in emphysema. The destruction of the alveolar walls reduces the elasticity of the lung overall.
Loss of elasticity leads to the collapse of the bronchioles, obstructing airflow out of the alveoli. Air becomes "trapped" in the alveoli and reduces the ability of the lung to shrink during exhalation. The reduced expansion of the lung during the next breath reduces the amount of air that is inhaled. As a result, less air for the exchange of gasses gets into the lungs. This trapped air also can compress adjacent less damaged lung tissue, preventing it from functioning to its fullest capacity.

The exchange of carbon dioxide and oxygen between air and the blood in the capillaries takes place across the thin walls of the alveoli. Destruction of the alveolar walls decreases the number of capillaries available for gas exchange. This adds to the decrease in the ability to exchange gases.

Usually, energy is only required for inhalation to inflate the lungs. The stretch of the lungs and distension of the chest cavity springs back to rest during exhalation, a passive process that does not require energy. However, in emphysema, inefficient breathing occurs because extra effort and energy has to be expended to empty the lungs of air due to the collapse of the airways. This essentially doubles the work of breathing, since now energy is required for both inhalation and exhalation. In addition, because of the reduced capacity to exchange gases with each breath (due to the collapse of the bronchioles and loss of capillaries), it is necessary to breathe more frequently.