A patient has a mean arterial pressure of 95 mmHg, cardiac output of 5 L/min, central venous pressure of 3 mmHg. What is the systemic vascular resistance in mmHg·min/L (Wood units)?

• A SVR = (95 − 3)/5 = 18.4 Wood units ✓
• B SVR = 95/5 = 19.0 Wood units
• C SVR = (95 − 3)/5 × 80 = 1472 dyne·s/cm⁵
• D SVR = (95 + 3)/5 = 19.6 Wood units

Explanation

SVR = (MAP − CVP) / CO = (95 − 3) / 5 = 92/5 = 18.4 Wood units (mmHg·min/L). This is the correct Ohm's law analog: resistance = pressure gradient / flow. The pressure gradient driving systemic blood flow is MAP minus CVP (outflow pressure), not just MAP alone. Option B ignores CVP. Option C provides the conversion to dyne·s/cm⁵ (multiply Wood units by 80), but the numerical calculation of the Wood units component is presented as if it is the SVR — it would give 18.4 × 80 = 1472 dyne·s/cm⁵, which is a valid conversion, but the question asks for Wood units. Option D incorrectly adds instead of subtracts CVP.

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

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