Calculate pulmonary blood flow (Qp) by the Fick principle, pulmonary vascular resistance (PVR) in Wood units, arterial O₂ content or the Qp:Qs ratio.

After the lungs. Enter oxygen content, not saturation (%).

Blood entering the lungs; sampling sites matter with shunts.

Flow result unit

Related Calculators

Pulmonary Flow Formula

The Fick principle estimates pulmonary flow Qp from oxygen consumption and the pulmonary venous–pulmonary arterial oxygen-content difference. Oxygen-content mode uses C O₂ = H × Hb × (S O₂/100) + 0.0031 × P O₂, with Hb in g/dL, saturation in %, P O₂ in mmHg, and content in mL O₂/dL. H is the selected 1.34 or 1.39 mL O₂/g Hb convention. Resistance mode uses PVR = (mPAP − PAWP)/Qp in Wood units, with pressures in mmHg and Qp in L/min; cardiac output is a proxy only when Qp = Qs without a shunt. Ratio mode directly divides entered Qp by Qs in matching units.

Qp (L / min) = VO₂ (mL O₂ / min) ÷ [CpvO₂ (mL O₂ / L blood) − CpaO₂ (mL O₂ / L blood)]

Variables:

  • Qp is pulmonary blood flow (L/min)
  • VO2 is the oxygen consumption (mL/min)
  • CpvO₂ is pulmonary venous oxygen content (mL O₂/L blood)
  • CpaO₂ is pulmonary arterial oxygen content (mL O₂/L blood)

With contents in mL O₂/L blood, VO₂ ÷ (CpvO₂ − CpaO₂) directly gives L/min. For mL O₂/dL inputs, multiply the content difference by 10 first. Multiply a final L/min result by 1000 only to display mL/min. VO₂ and the content difference must be positive.

What is Pulmonary Flow?

Pulmonary flow is the volume of blood passing through the pulmonary circulation per minute. It can differ from systemic flow when a shunt is present. Systemic arterial and mixed venous contents are suitable proxies for the pulmonary content pair only without a shunt and when clinically appropriate. Correct sampling and accurate oxygen consumption matter; assumed VO₂ and small oxygen-content differences can produce substantial error. The oxygen-content formula is an estimate and does not separately correct for dyshemoglobins.

How to Calculate Pulmonary Flow?

The following steps outline how to calculate the pulmonary flow:

  1. First, obtain oxygen consumption (VO₂) in mL O₂/min under stable measurement conditions; directly measured VO₂ is preferred to an assumed value.
  2. Next, obtain pulmonary venous oxygen content (CpvO₂), using the selected content unit.
  3. Then, obtain pulmonary arterial oxygen content (CpaO₂) under the same conditions and in the same unit.
  4. Divide VO₂ by the correctly converted content difference to calculate Qp in L/min.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Oxygen consumption (VO2) = 250 mL/min

Pulmonary venous oxygen content (CpvO₂) = 200 mL O₂/L blood

Pulmonary arterial oxygen content (CpaO₂) = 150 mL O₂/L blood. Qp = 250 ÷ (200 − 150) = 5 L/min (5000 mL/min). The equivalent contents are 20 and 15 mL O₂/dL.