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

Which condition bypasses systemic circulation and may cause pulmonary hypertension?

1. Left-to-Right Shunt

2. Compromised airways in Obstructive Airway Diseases

3. Anatomic Shunt

4. Decreased Alv Ventilation

The correct answer is: Left-to-Right Shunt

The condition that bypasses systemic circulation and may lead to pulmonary hypertension is characterized by a left-to-right shunt. In this scenario, blood flows from an area of higher pressure (typically the left side of the heart) to an area of lower pressure (the right side of the heart). This abnormal flow increases the volume of blood returning to the right side of the heart and subsequently the pulmonary circulation. The excess blood flow can elevate pulmonary artery pressure, thus causing pulmonary hypertension over time. In the case of a left-to-right shunt, common examples include congenital heart defects such as atrial septal defects (ASD) or ventricular septal defects (VSD). With these defects, the increased blood volume in the pulmonary vessels leads to vascular remodeling, increased pulmonary vascular resistance, and ultimately pulmonary hypertension if left uncorrected. Other conditions listed may contribute to respiratory issues but do not directly cause blood to bypass systemic circulation in a way that leads to pulmonary hypertension. Compromised airways in obstructive airway diseases and decreased alveolar ventilation primarily affect gas exchange rather than direct hemodynamic changes in the pulmonary circulation. An anatomical shunt can also involve bypassing the lungs but typically refers to situations where blood moves directly from the right side of the