Final answer:
Expiration, or pulmonary ventilation, is the respiratory process most impaired by emphysema. This condition damages the lung's air sacs, causing air to be trapped and making it difficult to push out during exhalation.
Step-by-step explanation:
The respiratory process impaired the most by emphysema is expiration (pulmonary ventilation). Emphysema is a condition where the air sacs of the lungs are damaged, leading to overinflated lungs, which makes it difficult for the lungs to push out air. This is because the compliance of the lung is changed; the airways don't recoil properly to expel the air trapped in the lungs. Consequently, this impairs the ability of the lungs to exert pressure back towards the interior during exhalation. Moreover, this obstruction leads to reduced gas exchange efficiency, typically observed in external respiration, as the transport of oxygen into the blood and the removal of carbon dioxide from the blood are hindered.