USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

What is the primary cause of shortness of breath in left ventricular heart failure (LVHF)?

1. Pulmonary fibrosis

2. Inadequate surfactant production

3. Caplan syndrome

4. Impaired diastolic return of pulmonary vein

The correct answer is: Impaired diastolic return of pulmonary vein

Shortness of breath in left ventricular heart failure (LVHF) is primarily caused by impaired diastolic return of blood from the lungs due to increased pressure in the left atrium. In LVHF, the left ventricle fails to effectively pump blood forward into the aorta, leading to a backlog of blood in the pulmonary circulation. This increased pressure in the pulmonary veins results in fluid transudation into the alveoli, which can cause pulmonary congestion and edema. The presence of fluid in the lungs impairs gas exchange, leading to shortness of breath, particularly during activities or when lying flat. While other conditions like pulmonary fibrosis or inadequate surfactant production could cause respiratory symptoms, they are not the primary drivers of the shortness of breath experienced in LVHF. Caplan syndrome, which is a specific type of pneumoconiosis, is also unrelated to the primary mechanisms of shortness of breath in the context of heart failure. The main physiological disturbance in LVHF—impaired diastolic return due to increased left atrial pressure—is critical in understanding this symptom.