What feature to maximize the volume of gases exchanged during internal expiration?

It can be defined as,"The exchange of gaseous(CO₂ and O₂) or diffusion of materials which occurs inside the body, between the interstitial spaces(along with capillaries) and the veins inside the blood circulatory system."

Explanation:

Difference in O₂ and Co₂ concentration inside the blood medium and the cells:

Diffusion occurs when there is a change of concentration or level of O₂ and Co₂.As there is more O₂ inside the blood,as compared to the O₂ present inside the interstitial spaces and the capillaries,so,it diffuses from the blood medium into the capillaries leading to there oxygenation. As the CO₂ level inside the cells and the interstitial spaces is more as compared to the low concentration of CO₂ in the blood,so, CO₂ diffuses from the capillaries to the vein leading it to the lungs.