Normal Pulmonary Vascular Resistance (PVR) Values
Normal pulmonary vascular resistance (PVR) is less than 3 Wood units (WU), with values ≥3 WU considered diagnostic for pulmonary hypertension according to established guidelines. 1
Definition and Measurement
PVR is a critical hemodynamic parameter that reflects the resistance to blood flow through the pulmonary vasculature. It is calculated using the following formula:
- PVR = (mean Pulmonary Arterial Pressure - Pulmonary Artery Wedge Pressure) / Cardiac Output
Key points about normal PVR:
- Measured in Wood units (WU), also sometimes expressed as mmHg·min/L
- Requires right heart catheterization for accurate measurement
- Normal range: <3 WU 2, 1
- Recent research suggests that PVR values around 2.2 WU may already indicate increased risk 3
Clinical Classification Based on PVR
PVR plays a crucial role in classifying pulmonary hypertension:
Normal PVR: <3 WU
Pre-capillary pulmonary hypertension:
Post-capillary pulmonary hypertension:
- mPAP ≥25 mmHg
- PAWP >15 mmHg
- Variable PVR 1
- Typically seen in left heart disease (Group 2)
Clinical Significance of PVR Values
- <3 WU: Normal pulmonary vascular resistance
- 3-10 WU: Mild to moderate elevation, may be seen in early pulmonary arterial hypertension
- 10-14 WU: Significant elevation, often used as a threshold when considering surgical intervention for congenital heart disease 2
- >14 WU: Severe elevation, often associated with poor prognosis
Emerging Research on PVR Thresholds
Recent evidence suggests that the risk associated with elevated PVR may begin at lower values than previously thought:
- PVR ≥2.2 WU has been associated with increased mortality risk (HR 1.71,95% CI 1.59-1.84) even in patients with normal PAWP ≤15 mmHg 3
- Patients with "borderline" PVR (below the 3 WU threshold but with elevated mPAP) may still have adverse outcomes and potentially benefit from treatment 4
Clinical Applications of PVR Measurement
PVR is essential for:
- Diagnosing pulmonary hypertension
- Classifying the type of pulmonary hypertension
- Assessing disease severity
- Evaluating treatment response
- Determining prognosis 1
- Assessing operability in congenital heart disease (threshold often set at 10-14 WU) 2
Important Considerations
- PVR is flow-dependent, meaning it can change with alterations in cardiac output
- In high-flow states (exercise, anemia, pregnancy), PVR may decrease despite unchanged pulmonary vascular anatomy
- In congenital heart disease, PVR may appear lower due to high pulmonary blood flow despite significant pulmonary vascular disease 2
- Right heart catheterization remains the gold standard for accurate PVR measurement, though non-invasive echocardiographic methods are being developed 5, 6
Understanding normal and abnormal PVR values is crucial for proper diagnosis and management of pulmonary vascular disease, with values ≥3 WU indicating abnormal pulmonary vascular resistance requiring further evaluation and potential treatment.