What is the normal value of pulmonary vascular resistance (PVR)?

Normal Values of Pulmonary Vascular Resistance (PVR)

The normal value of pulmonary vascular resistance (PVR) is less than 3 Wood units (WU). 1

Definition and Measurement

Pulmonary vascular resistance is a critical hemodynamic parameter that quantifies the resistance to blood flow through the pulmonary vasculature. It is calculated using measurements obtained during right heart catheterization (RHC), which remains the gold standard for assessment.

Calculation Formula:

• PVR = (mean Pulmonary Arterial Pressure - Pulmonary Artery Wedge Pressure) / Cardiac Output
• Units: Wood units (WU) or dynes·sec·cm⁻⁵ (1 WU = 80 dynes·sec·cm⁻⁵)

Normal Range and Diagnostic Thresholds

According to current guidelines:

• Normal PVR: <3 Wood units 1
• Abnormal PVR: ≥3 Wood units (diagnostic threshold for pulmonary hypertension) 2, 1

The European Society of Cardiology (ESC) and European Respiratory Society (ERS) guidelines define pre-capillary pulmonary hypertension as:

• Mean pulmonary arterial pressure (mPAP) ≥25 mmHg
• Pulmonary artery wedge pressure (PAWP) ≤15 mmHg
• PVR >3 Wood units 2

Clinical Significance

PVR values have significant clinical implications:

• PVR <3 WU: Normal pulmonary vascular resistance
• PVR 3-5 WU: Mild elevation, may indicate early pulmonary vascular disease
• PVR 5-10 WU: Moderate elevation, significant pulmonary vascular disease
• PVR >10 WU: Severe elevation, advanced pulmonary vascular disease with poor prognosis 1

Interpretation in Different Clinical Contexts

The interpretation of PVR should be considered alongside other hemodynamic parameters:

1. Pre-capillary Pulmonary Hypertension:

   • Elevated mPAP (≥25 mmHg)
   • Normal PAWP (≤15 mmHg)
   • Elevated PVR (>3 WU)
   • Seen in pulmonary arterial hypertension (Group 1) and chronic thromboembolic pulmonary hypertension (Group 4) 2

2. Post-capillary Pulmonary Hypertension:

   • Elevated mPAP (≥25 mmHg)
   • Elevated PAWP (>15 mmHg)
   • Variable PVR
   • Typically seen in left heart disease (Group 2) 2

Clinical Examples from Guidelines

The ESC/ERS guidelines provide examples of typical hemodynamic values in different clinical scenarios:

• In a case study of a patient with chronic thromboembolic pulmonary hypertension, baseline PVR was 299 dynes·sec·cm⁻⁵ (approximately 3.7 WU) 2
• After successful pulmonary endarterectomy, PVR values typically decrease to 200-300 dynes·sec·cm⁻⁵ (2.5-3.75 WU) 2

Importance in Treatment Decisions

PVR is crucial for:

• Diagnosis of pulmonary hypertension
• Classification of pulmonary hypertension type
• Assessment of disease severity
• Evaluation of treatment response
• Prognostication 1

Non-invasive Estimation

While RHC remains the gold standard, echocardiographic methods have been developed to estimate PVR non-invasively:

• These methods typically use the tricuspid regurgitation velocity and right ventricular outflow tract velocity-time integral 3, 4
• While useful for screening, they may underestimate high PVR values and should not replace RHC for definitive diagnosis 4

Key Points to Remember

• PVR >3 WU is the established threshold for defining abnormal pulmonary vascular resistance
• PVR must be interpreted alongside other hemodynamic parameters (mPAP, PAWP)
• Right heart catheterization remains the gold standard for accurate PVR measurement
• PVR is essential for proper classification, risk assessment, and management of pulmonary hypertension