What does PVR (Peripheral Vascular Resistance) stand for in vascular medicine?

What Does PVR Stand For in Vascular Medicine?

PVR has two distinct meanings in vascular medicine: Pulse Volume Recording (a noninvasive test for peripheral arterial disease) and Pulmonary Vascular Resistance (a hemodynamic measurement for pulmonary hypertension diagnosis). The context determines which meaning applies, and confusing these terms can lead to serious clinical errors.

Pulse Volume Recording (PVR) - Peripheral Arterial Disease

Pulse Volume Recording is a noninvasive physiological test that detects peripheral arterial disease by measuring limb volume changes with each pulse. 1

How the Test Works

• Pneumoplethysmography cuffs are inflated at predetermined levels on each limb, measuring miniscule volume changes with each pulse to create waveform tracings 2
• The technique relies on limb volume change rather than pressure, making it particularly valuable when ankle-brachial index fails in patients with noncompressible vessels 2
• This is especially useful in patients with diabetes and chronic renal insufficiency where vessel calcification prevents accurate pressure measurements 2

Waveform Interpretation

• Normal waveforms show sharp upstrokes and prominent dicrotic notches 2
• Abnormal waveforms demonstrate blunted upstrokes, absent dicrotic notches, and decreased amplitude, indicating hemodynamically significant stenosis proximal to that level 2
• Compare waveforms at sequential levels to determine segmental disease location and assess arterial blood flow quality at each station simultaneously 2

Clinical Applications

• Use PVR in conjunction with ankle-brachial index and segmental pressure measurements for comprehensive peripheral arterial disease assessment 2
• PVR is especially useful when ankle-brachial index >1.3 indicates noncompressible vessels 2
• The test provides insight into disease location but cannot determine precise severity or number of lesions 2
• PVR tracings have been found extremely useful in establishing success of therapy and in long-term follow-up of patients with arteriosclerotic peripheral vascular disease 3

Pulmonary Vascular Resistance (PVR) - Pulmonary Hypertension

Pulmonary Vascular Resistance is a calculated hemodynamic parameter essential for diagnosing pulmonary arterial hypertension, measured in Wood units. 1, 4

Calculation Formula

• PVR = (mean pulmonary artery pressure - pulmonary capillary wedge pressure) / cardiac output 4
• Units are expressed as Wood units (normal <2-3 Wood units) or dynes·s·cm⁻⁵ (multiply Wood units by 80 for conversion) 1, 4
• The European Society of Cardiology and European Respiratory Society recommend using Wood units to simplify calculations and reduce mathematical errors 4

Required Measurements

• Mean pulmonary artery pressure (mPAP) must be measured via right heart catheterization—this is the gold standard and only validated method 4, 2
• Pulmonary capillary wedge pressure (PCWP) is obtained by wedging a balloon-tipped catheter into a small pulmonary arterial branch with the balloon inflated 4
• Cardiac output should be measured in L/min, typically via thermodilution or Fick method 4
• All measurements must be obtained via right heart catheterization—echocardiographic estimates are unreliable for diagnosis 2

Diagnostic Thresholds

• PVR >3 Wood units combined with mean pulmonary artery pressure >25 mmHg defines pulmonary arterial hypertension (2015 guidelines) 1, 2
• The 2024 guidelines define precapillary pulmonary hypertension as PVR >2 Wood units 4
• A PCWP >15 mmHg excludes the diagnosis of precapillary pulmonary arterial hypertension 4

Clinical Decision Points

• PVR >2.5 Wood units or >4 Wood units·m² indexed is a contraindication for congenital heart disease shunt closure 4
• PVR distinguishes passive pulmonary hypertension (elevated mPAP, normal PVR) from pulmonary vascular disease (elevated mPAP, elevated PVR) 2
• Transpulmonary gradient (mPAP - PCWP) >20 mmHg with PVR >3 Wood units indicates disproportionate pulmonary vascular involvement even in left heart disease 2

Pulmonary Vascular Resistance Index (PVRI)

PVRI is the indexed value of pulmonary vascular resistance adjusted for body surface area, measured in Wood units·m² (WU·m²). 4, 5

Clinical Thresholds

• PVRI <6 WU·m² is an indicator for repair in children with structural heart disease (ASD, VSD, PDA) 4
• PVRI ≥6 WU·m² indicates that repair is not indicated unless acute vasodilator testing demonstrates reversibility (absolute PVRI <6 WU·m² and PVR/SVR <0.3) 4
• PVRI >6 WU·m² predicts poor prognosis in children with congenital heart disease, regardless of lung morphology 4

Units Confusion in Literature

• Significant variability exists among the units used to report PVRI in current literature, with 54.6% of sources reporting PVRI with incorrect units (not ending in m²) 5
• This lack of uniformity has led to considerable confusion among researchers and clinicians, with potentially life-altering consequences 5
• The indexed value (PVRI) is particularly important in pediatric populations where body size varies significantly and affects hemodynamic measurements 4

Critical Measurement Considerations

Technical Pitfalls

• In patients with tricuspid regurgitation and right ventricular dilatation, thermodilution cardiac output measurements can be erroneous, compromising PVR calculation accuracy 2
• During mechanical ventilation with high PEEP, calculate transmural PCWP to estimate true left ventricular filling pressure 2
• Blood pH has a potent effect on pulmonary vascular tone—acidosis causes vasoconstriction while alkalosis causes vasodilation 4
• Measurements should be obtained under standardized conditions, as general anesthesia can lower systemic arterial blood pressure and affect resistance calculations 4

When Direct Left Atrial Pressure Measurement is Needed

• Direct left atrial pressure or LVEDP measurement is recommended in patients where left heart disease is the likely etiology, such as those with orthopnea or associated risk factors 4
• Direct measurement is indicated when there is doubt about the accuracy of PCWP, elevation of pulmonary artery pressure is out of proportion to mean gradient and valve area, or clinical and hemodynamic findings are discrepant 4

Common Clinical Pitfalls

• Never confuse Pulse Volume Recording (peripheral arterial test) with Pulmonary Vascular Resistance (hemodynamic calculation) 1, 4
• Echocardiographic estimation of pulmonary artery systolic pressure has limited positive predictive value (25-64%) for confirming pulmonary hypertension and should not replace right heart catheterization for PVR calculation 1, 2
• Acute hemodynamic evaluation provides only a snapshot and may not represent overall clinical status 4
• Volume status assessment in pulmonary hypertension patients is notoriously difficult, and non-invasive estimates of central venous pressures may be misleading, requiring direct central line measurement 4