At the beginning of the forced expiration

lung elastic recoil increases

airway resistance decreases

intrathoracic airway widen

transmural airway pressure remains low

O2 pressure increase in airways

At the beginning of forced expiration Lung elastic recoil increases

During forced expiration, the muscles of respiration contract to actively decrease the volume of the thoracic cavity.

However, at the beginning of forced expiration, the lung elastic recoil, which is the natural tendency of the lungs to recoil inward, increases.

This recoil helps to push air out of the lungs by reducing the volume of the thoracic cavity.