Final answer:
Decreased or asymmetrical chest expansion can be caused by conditions that affect lung compliance and chest wall mechanics, such as spontaneous pneumothorax, pulmonary fibrosis, and respiratory distress syndrome. These conditions lead to stiffened lung tissue or interruptions in normal pressure dynamics, resulting in impaired lung expansion and gas exchange.
Step-by-step explanation:
Decreased or asymmetrical chest expansion may result from various pulmonary conditions affecting the lungs and chest wall mechanics. When the muscles of the thorax, specifically the diaphragm and intercostal muscles, relax, they cause the intrathoracic pressure to drop, expanding the chest wall and allowing air to be drawn into the airways. However, in certain conditions like pulmonary fibrosis, respiratory distress syndrome, or spontaneous pneumothorax, the compliance of the lung tissue is compromised due to stiffening or injury that prevents normal expansion.
In conditions like pulmonary fibrosis, the lung tissue becomes fibrotic and loses its ability to expand and contract effectively, resulting in reduced lung volumes such as the force vital capacity (FVC). Spontaneous pneumothorax, or collapsed lung, can also cause decreased chest expansion due to a disruption in the negative pressure system of the pleural space, often related to connective tissue abnormalities. In cases where a physiological shunt is present due to infection or edema, there may be a decrease in ventilation without affected perfusion, leading to a V/Q mismatch and compromised gas exchange.