CAMRT Radiography Practice Exam

What effect does free air in the pleural cavity have on lung tissue density?

1. It increases lung density

2. It reduces lung density

3. It has no effect on lung density

4. It alters the position of the diaphragm

The correct answer is: It reduces lung density

Free air in the pleural cavity, commonly known as pneumothorax, occurs when air enters the pleural space, the thin space between the lungs and the chest wall. When this happens, it can disrupt the normal relationship between the lung tissue and the pleural cavity. As air fills the pleural space, it pushes against the lung tissue, leading to a collapse of the affected lung, which reduces the volume and density of the lung tissue itself. This collapse means that the air-filled spaces in the lung (such as alveoli) are diminished or unable to fill properly with air, leading to a reduction in lung density. Consequently, less lung tissue is available to absorb x-rays, making the lung appear less dense on radiographic imaging. While the presence of free air certainly can impact diaphragm position (as noted in one of the other possible answer choices), its primary influence in terms of lung density is through the displacement and collapse of lung tissue, ultimately reducing lung density.