Vascular Resistance (SVR & PVR) Calculator
Compute systemic (SVR) and pulmonary (PVR) vascular resistance from mean pressures and cardiac output. Fill the pulmonary fields only if you need PVR.
What is vascular resistance?
Vascular resistance is the opposition the circulation offers to blood flow — the "afterload" the heart pumps against. There are two of them: systemic vascular resistance (SVR) for the body\u2019s circulation and pulmonary vascular resistance (PVR) for the lungs. Both are derived from a pressure difference divided by flow, exactly like Ohm\u2019s law (resistance = voltage ÷ current) applied to blood.
Formulas
- SVR = (MAP − CVP) ÷ cardiac output × 80 (dynes·s·cm⁻⁵)
- PVR = (mean PAP − PCWP) ÷ cardiac output × 80 (dynes·s·cm⁻⁵)
The pressure difference is the drop across that circuit — MAP minus right-atrial (CVP) pressure for the body, mean pulmonary artery pressure minus wedge pressure for the lungs. The ×80 converts the result into the conventional units. Drop the ×80 and PVR is expressed in Wood units instead.
Normal values
| Resistance | Normal |
|---|---|
| SVR | 800–1200 dynes·s·cm⁻⁵ |
| PVR | < 250 dynes·s·cm⁻⁵ (< ~3 Wood units) |
How to read the numbers
Resistance ties pressure and flow together, so it is the key to sorting out shock:
- Low SVR + high/normal output — the warm, vasodilated picture of distributive (septic) shock. Treated with vasopressors that raise resistance.
- High SVR + low output — the body clamps down to defend blood pressure, as in cardiogenic or hypovolaemic shock.
- High PVR — pulmonary hypertension or lung disease, raising the load on the right ventricle.
For the full derivation and clinical use, read the systemic vascular resistance guide, and pair this with the MAP calculator and cardiac output calculator.
References
- Standard critical-care and hemodynamic-monitoring references. AHA.
Educational reference only — not a substitute for clinical judgement.
Frequently asked questions
How do you calculate systemic vascular resistance?
SVR = (mean arterial pressure − central venous pressure) ÷ cardiac output × 80, expressed in dynes·s·cm⁻⁵.
What is a normal SVR?
Roughly 800–1200 dynes·s·cm⁻⁵. A low SVR suggests distributive shock such as sepsis, while a high SVR fits cardiogenic or hypovolaemic shock.
How do you calculate pulmonary vascular resistance?
PVR = (mean pulmonary artery pressure − pulmonary capillary wedge pressure) ÷ cardiac output × 80; normal is under about 250 dynes·s·cm⁻⁵.
What is a normal PVR?
Under about 250 dynes·s·cm⁻⁵, or less than roughly 3 Wood units. A raised PVR indicates pulmonary hypertension or lung disease.
What are Wood units?
Wood units express PVR without the ×80 conversion: PVR (Wood units) = (mean PA pressure − wedge pressure) ÷ cardiac output. Multiply by 80 to get dynes·s·cm⁻⁵.
Why multiply by 80 in the resistance formula?
The factor of 80 converts the pressure-over-flow result (mmHg per L/min) into the conventional CGS units of dynes·s·cm⁻⁵.
What does a low SVR mean?
A low systemic vascular resistance means the vessels are dilated. With a normal or high cardiac output it points to distributive shock, most commonly sepsis, and is treated with vasopressors.