A 28-year-old woman with primary pulmonary hypertension has a mean pulmonary artery pressure of 45 mmHg. If her cardiac output is 4.0 L/min, pulmonary capillary wedge pressure is 8 mmHg, and mean right atrial pressure is 12 mmHg, what is her pulmonary vascular resistance (PVR) in Wood units?

• A 5.25 Wood units
• B 9.25 Wood units ✓
• C 8.33 Wood units
• D 11.0 Wood units

Explanation

PVR = (Mean PAP − PCWP) / Cardiac Output = (45 − 8) / 4.0 = 37/4.0 = 9.25 Wood units. The formula uses the pressure gradient across the pulmonary circuit (mean PAP minus pulmonary wedge pressure) divided by cardiac output in L/min. Option A uses the wrong pressure (45 − 24)/4 = 5.25. Option C incorrectly subtracts RA pressure instead of PCWP: (45 − 12)/4 = 8.25, not 8.33. The right atrial pressure is used to calculate systemic vascular resistance, not PVR. Normal PVR is less than 3 Wood units; 9.25 confirms severe pulmonary hypertension.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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