Final answer:
An expected finding during chest excursion is true expansion of the lungs. The combination of diaphragm contraction and chest wall expansion causes air to rush into the lungs, while relaxation leads to expiration.
Step-by-step explanation:
When assessing chest excursion, an expected finding is that the lungs expand during inhalation - this is true. The chest wall expands out and the lungs, which are elastic, fill with air due to the contraction of the diaphragm and the external intercostal muscles. As the chest wall expands and the diaphragm contracts, the volume of the thoracic cavity increases, the pressure within the lungs decreases, and air rushes in due to the pressure gradient relative to the environment. During expiration, which is typically a passive process, the lungs recoil to expel the air, while the intercostal muscles relax and the diaphragm moves upward, increasing the thoracic pressure and pushing air out.