What is the primary cause of pulmonary edema?

The primary cause of pulmonary edema is the accumulation of fluid in the lungs due to left heart failure. When the left side of the heart is unable to pump blood efficiently, it can cause pressure to build up in the pulmonary veins. This increased pressure pushes fluid from the blood vessels into the air sacs (alveoli) of the lungs, leading to pulmonary edema. This condition can impair gas exchange, causing symptoms such as shortness of breath, coughing, and difficulty breathing.

In comparison, infections in the lungs and conditions such as chronic bronchitis primarily affect lung function and inflammation but do not directly lead to the fluid accumulation characteristic of pulmonary edema. Obstruction of the airway can lead to respiratory distress, but again, it is not the mechanism that causes fluid buildup in the lung tissue itself. Therefore, the scenario outlined in option B accurately reflects the pathophysiological relationship between heart failure and pulmonary edema.