PAH Hemodynamics Calculator
Estimate pulmonary vascular resistance (PVR) and review whether invasive hemodynamic values are compatible with a pre-capillary pulmonary hypertension pattern that may include PAH.
Educational use only. This tool does not diagnose disease and does not replace right-heart catheter interpretation by a qualified clinician.
What this PAH calculator does
This PAH calculator is built to help you quickly compute the numbers most often discussed in invasive pulmonary hemodynamics: Transpulmonary Gradient (TPG) and Pulmonary Vascular Resistance (PVR). These values are commonly used when evaluating pulmonary hypertension patterns.
While people search for a “PAH calculator,” it is important to understand that no single formula can confirm pulmonary arterial hypertension by itself. PAH is a clinical diagnosis that requires complete workup, including history, imaging, exclusion of secondary causes, and specialist interpretation.
Formulas used
1) Transpulmonary Gradient (TPG)
TPG = mPAP − PAWP
2) Pulmonary Vascular Resistance
PVR (Wood Units) = (mPAP − PAWP) / CO
PVR (dyn·s·cm⁻⁵) = PVR (Wood Units) × 80
Current hemodynamic definitions generally consider pulmonary hypertension when mPAP > 20 mmHg. A pre-capillary profile includes PAWP ≤ 15 mmHg and PVR > 2 Wood Units.
How to use this calculator
- Enter mPAP from right-heart catheterization data.
- Enter PAWP measured during the same study.
- Enter cardiac output in L/min (thermodilution or Fick, as documented).
- Click Calculate to view TPG, PVR, and an interpretation summary.
Interpreting your results carefully
When results may look “compatible with PAH”
If mPAP is above 20 mmHg, PAWP is 15 mmHg or less, and PVR is above 2 Wood Units, the pattern can be compatible with pre-capillary pulmonary hypertension. That profile is seen in PAH, but also in other pre-capillary causes depending on clinical context.
When results suggest post-capillary involvement
If PAWP is above 15 mmHg with elevated mPAP, this may point toward a post-capillary component, often associated with elevated left-heart filling pressures. This does not exclude complex or mixed physiology, so full interpretation still matters.
Why PVR matters in a PAH calculator
PVR approximates how much resistance the right ventricle must overcome to push blood through the pulmonary circulation. Higher resistance generally reflects greater strain on right-heart function. Tracking PVR over time can be useful when clinicians assess disease progression or response to therapy.
Common input mistakes to avoid
- Unit mismatch: Ensure cardiac output is in L/min.
- Mixed timestamps: Use values from the same hemodynamic assessment.
- Data entry errors: A swapped number (e.g., PAWP and mPAP) can produce impossible physiology.
- Over-interpretation: A calculator output is a screening aid, not a final diagnosis.
Frequently asked questions
Can this tool diagnose PAH?
No. It only performs mathematical checks and pattern guidance from entered hemodynamics.
Why does the result mention “compatible with” instead of “confirmed”?
Because PAH confirmation requires full specialist evaluation and exclusion of alternative causes.
What if my PAWP is higher than mPAP?
That can indicate measurement or entry issues and should be reviewed carefully. The calculator will still compute values, but interpretation may be unreliable.
Bottom line
A good PAH calculator should be fast, transparent, and clinically humble. Use this page to compute TPG and PVR, then bring the output into a broader clinical conversation rather than treating it as a stand-alone answer.