In which condition will you likely observe a decreased total lung capacity (TLC)?

Decreased total lung capacity (TLC) is a hallmark of restrictive lung diseases. In these conditions, there is a limitation in lung expansion due to alterations in the lung tissue itself or the pleura, chest wall, or respiratory muscles, leading to a reduced ability to move air in and out of the lungs adequately. This results in a smaller volume of air that can be contained within the lungs during both inspiration and expiration, thus lowering the TLC.

Restrictive lung diseases include a variety of conditions, such as pulmonary fibrosis, interstitial lung disease, and conditions affecting the pleura (like pleural effusion or pneumothorax). In these scenarios, the lung structures become less compliant, restricting the overall lung volumes, including TLC.

In contrast, conditions like acute bronchospasm and obstructive lung disease typically result in increased lung volumes, due to air trapping and hyperinflation, which is why TLC would not be decreased. Cardiac-induced pulmonary edema might lead to other changes in lung volumes but doesn’t typically cause a direct decrease in TLC as seen in restrictive lung disease.