SVR stands for which hemodynamic term?

• A. Systemic venous resistance
• B. Systemic vascular resistance
• C. Stroke volume resistance
• D. Systemic vascular ratio

Answer: (B)

Systemic vascular resistance is the resistance the systemic circulation offers to blood flow, i.e., the afterload the left ventricle must overcome to eject blood. It is determined by arterial tone and the caliber of the systemic arterioles. The concept is captured by the pressure-flow relationship: SVR = (mean arterial pressure − right atrial pressure) / cardiac output. In practice, SVR is reported in Wood units (mmHg·min/L) or dynes·s·cm⁻⁵ (where Wood units × 80 ≈ dynes·s·cm⁻⁵). This matters because vasoconstriction increases SVR and afterload, reducing stroke volume for a given preload, while vasodilation decreases SVR and afterload.

The other terms aren’t standard: the phrase systemic venous resistance isn’t a commonly used measure, systemic vascular ratio isn’t a recognized hemodynamic term, and stroke volume resistance isn’t a defined parameter. Pulmonary vascular resistance refers to the resistance in the pulmonary circulation, not the systemic.