Calculate Pulmonary Artery Pressure

Calculate Pulmonary Artery Pressure

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Calculate Pulmonary Artery Pressure

Calculate Pulmonary Artery Pressure (PAP) from Peak Tricuspid Regurgitation (TR) Velocity– use the modified Bernoulli equation:

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🧮 Formula:

PASP (Pulmonary Artery Systolic Pressure) =
👉 4 × (TR velocity)² + RAP

Where:

• TR velocity = Peak tricuspid regurgitation velocity (in m/s)
• RAP = Estimated right atrial pressure (in mmHg)

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📌 Step-by-Step:

1. Measure Peak TR Velocity using Doppler echocardiography.
2. Square the TR velocity.
3. Multiply it by 4 → this gives the pressure gradient between RV and RA.
4. Add estimated RAP (commonly 3, 8, or 15 mmHg depending on IVC size and collapsibility).

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✅ Example:

• TR velocity = 3.2 m/s
• RAP = 10 mmHg (based on IVC assessment)

PASP = 4 × (3.2)² + 10 = 4 × 10.24 + 10 = 40.96 + 10 = ~51 mmHg

➡️ Pulmonary Artery Systolic Pressure = 51 mmHg

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🎯 Interpretation:

PASP (mmHg)	Interpretation
< 35	Normal
35–50	Mild Pulmonary Hypertension
50–70	Moderate Pulmonary Hypertension
> 70	Severe Pulmonary Hypertension

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📖 Notes:

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• This formula estimates systolic PAP, not mean or diastolic.
• RAP is often estimated using IVC diameter and collapsibility with sniff:
  • <2.1 cm and collapses >50% → RAP ≈ 3 mmHg
  • >2.1 cm and collapses <50% → RAP ≈ 15 mmHg
  • Intermediate findings → RAP ≈ 8 mmHg

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Severity of pulmonary hypertension (mPAP)

• Mild = 20-40mmHg
• Moderate = 41-55mmHg
• Severe = > 55mmHg

MEASUREMENT OF PULMONARY ARTERY PRESSURE

Calculation of PAP from Peak tricuspid regurgitation velocity (ms-1)

• Doppler Echo can approximate pulmonary artery systolic pressure (PASP) using
  • tricuspid valve velocity (4v2 = TV pressure gradient)
  • estimated CVP (=RA pressure)
  • Bernoulli equation
• PASP = RVSP (in the absence of RVOTO or pulmonic stenosis)
  • RVSP = 4v2 + CVP
• Mean PAP can be approximated because PAPm = 0.61•sPAP + 2.
  • A systolic PAP of 30 mm Hg typically implies a mean PAP more than 20 mm Hg, i.e. pulmonary hypertension

Echocardiographic probability of pulmonary hypertension (PH) in symptomatic patients with a suspicion of PH (from Frost et al, 2019)

Peak tricuspid regurgitation velocity ms-1	Other “PH echo signs” present	Echo probability of PH
<=2.8 or not measurable	No	Low
<=2.8 or not measurable 2.9-3.4	Yes No	Intermediate
2.9-3.4 >=3.4	Yes Not required	High

The mean and end diastolic pressures in the pulmonary artery are directly assessed by measuring peak and end-diastolic velocities of the pulmonary regurgitant (PR) jet

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Calculating pulmonary artery pressure

• Pulmonary Hypertension (PH): Condition of elevated blood pressure in the pulmonary arteries, generally defined by a resting mean pulmonary artery pressure (mPAP) >20 mm Hg measured by right heart catheterization (RHC).
• Pulmonary Arterial Hypertension (PAH): A specific form of PH affecting the pulmonary arteries, characterized by pre-capillary PH (mPAP >20 mmHg, PAWP ≤15 mmHg, PVR >2 WU).
• Right Heart Catheterization (RHC): The gold standard for definitive diagnosis and measurement of pulmonary artery pressures.
• Echocardiography (TTE): A non-invasive imaging technique used to estimate pulmonary artery pressure and assess right heart function, often serving as a screening tool. 

Key measurements and calculations

• Mean Pulmonary Artery Pressure (mPAP): Calculated during RHC. Can also be estimated using various echocardiographic formulas involving PASP, dPAP, TR velocity, PR velocity, RVOT acceleration time (ATRVOT), and Right Atrial Pressure (RAP).
  • Formula (from RHC): mPAP = dPAP + 1/3 (sPAP – dPAP) or mPAP = 2/3 dPAP + 1/3 sPAP.
  • Formula (estimated from echo): mPAP = 0.61 * PASP + 2 mmHg.
• Pulmonary Artery Systolic Pressure (PASP): The peak pressure in the pulmonary artery during systole, usually calculated from the maximum velocity of the tricuspid regurgitant jet (TRmax) using the Bernoulli equation (P = 4[TRmax]2) and adding the estimated RAP.
• Pulmonary Artery Diastolic Pressure (PADP): The minimum pressure in the pulmonary artery during diastole, which can be estimated using the end-diastolic velocity of the pulmonary regurgitant (PR) jet (PR-end velocity) and RAP.
• Pulmonary Artery Wedge Pressure (PAWP): Measured during RHC, reflecting left atrial pressure and used to differentiate between pre-capillary and post-capillary PH.
• Right Atrial Pressure (RAP): Estimated from IVC dimensions and respiratory variations, or measured during RHC.
• Pulmonary Vascular Resistance (PVR): Calculated as (mPAP – mean PAWP)/cardiac output. An elevated PVR (typically >3 Wood units (WU) or >2 WU) suggests pulmonary vasculature as the primary pathology. 

Echocardiographic techniques and measurements

• Tricuspid Regurgitation (TR) Jet Velocity: Peak velocity (TRmax) used to estimate PASP.
• Pulmonary Regurgitation (PR) Jet Velocity: Peak and end-diastolic velocities used to estimate mPAP and PADP, respectively.
• Right Ventricular Outflow Tract (RVOT) Acceleration Time (ATRVOT): Measured from the onset of flow to peak velocity in the RVOT, an inverse correlate of mPAP.
• RV Free Wall Strain (Sm, SmVTI): Measures of RV myocardial function potentially useful in assessing elevated PASP.
• Right Ventricular Isovolumic Relaxation Time (rIVRT): A measure of RV relaxation, prolonged in PH.
• Tei Index (RV): An index of global RV performance, calculated from isovolumic contraction time, isovolumic relaxation time, and ejection time.
• RV/LV Basal Diameter Ratio and LV Eccentricity Index: Indicate RV pressure and volume overload leading to septal flattening.
• Right Atrial (RA) Area: An indicator of RA dilation.
• Inferior Vena Cava (IVC) Diameter and Respiratory Variability: Used to estimate RAP. 

Associated conditions and risk factors

• Connective Tissue Disease (CTD), especially Scleroderma (SSc): Higher risk of developing PH.
• Congenital Heart Disease (CHD): Can lead to PH, sometimes classified under group 1 or 2.
• Chronic Liver Disease and Portal Hypertension: Risk factors for PAH.
• HIV Infection: Another risk factor for PAH. 

Diagnostic tools

• Electrocardiogram (ECG): Can show signs like right-axis deviation associated with PH.
• Pulmonary Function Tests (PFTs) with DLCO: Helpful in differentiating PH groups and assessing lung disease.
• Chest Radiography and CT Scans: Can reveal pulmonary artery enlargement and other signs associated with PH.
• Ventilation-Perfusion (V̇/Q̇) Lung Scintigraphy: Distinguishes chronic thromboembolic pulmonary hypertension (CTEPH) from other PH types.
• Cardiopulmonary Exercise Testing (CPET): Provides valuable information regarding exercise capacity and PH severity. 

Additional considerations

• Vasoreactivity Testing: Done during RHC for patients with IPAH to identify responders to calcium channel blockers.
• Risk Stratification: Factors like functional class, exercise capacity, hemodynamics, right ventricular function, and biomarkers like BNP are used to predict outcomes and guide treatment. 

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