Final answer:
Chest expansion in the posterior thorax is assessed by observing thoracic wall movement during breathing, which reflects the compliance of the thoracic wall and efficiency of pulmonary ventilation.
Step-by-step explanation:
To assess chest expansion in the posterior thorax, one must understand the mechanics of breathing and thoracic wall compliance. Thoracic wall compliance is a key factor, as it is the ability of the thoracic wall to stretch under pressure, thereby influencing the capacity of the lungs to expand during breathing. The muscles of the thorax, including the intercostal muscles and the diaphragm, facilitate breathing by altering the size of the thoracic cavity.
During inspiration, the chest wall expands outward, and as a consequence, the intrapleural pressure drops, allowing air to flow into the airways. This expansion directly influences lung capacity. Conversely, during expiration, the lungs recoil and the chest wall returns to its resting position, thus expelling air. The muscles involved do not contract during this phase; it is a passive event, driven by the relaxation of these muscles and the elastic recoil of the lung tissue.
To assess posterior chest expansion, one typically observes the movement of the thorax during breathing, looking for symmetry and the extent of movement, which is indicative of thoracic wall and pulmonary ventilation efficiency. This clinical observation can be crucial in detecting abnormalities in breathing mechanics.