What is the Pulmonary Vascular Resistance (PVR) if the mean Pulmonary Artery Pressure (mPAP) is 33 mmHg, Pulmonary Artery Wedge Pressure (PAWP) is 2 mmHg, and Cardiac Output (CO) is 3.80 L/min?

Calculating Pulmonary Vascular Resistance (PVR)

The PVR for a patient with mPAP of 33 mmHg, wedge pressure of 2 mmHg, and cardiac output of 3.80 L/min is 8.16 Wood units.

Formula and Calculation

The calculation of Pulmonary Vascular Resistance (PVR) follows a standard formula recognized in cardiopulmonary hemodynamics:

PVR = (mPAP - PAWP) / CO

Where:

• mPAP = mean Pulmonary Artery Pressure (33 mmHg)
• PAWP = Pulmonary Artery Wedge Pressure (2 mmHg)
• CO = Cardiac Output (3.80 L/min)

Therefore: PVR = (33 - 2) / 3.80 = 31 / 3.80 = 8.16 Wood units

Clinical Significance

This PVR value of 8.16 Wood units is significantly elevated. According to guidelines, normal PVR is typically less than 3 Wood units 1. This elevation indicates substantial pulmonary vascular disease and has important clinical implications:

• The value exceeds the diagnostic threshold for pulmonary hypertension (PH) with PVR >3 Wood units 1
• This level of PVR elevation is associated with increased mortality risk 2
• The transpulmonary gradient (mPAP - PAWP = 31 mmHg) is markedly elevated, confirming pre-capillary pulmonary hypertension 1

Diagnostic Classification

Based on the hemodynamic values provided:

• mPAP ≥25 mmHg (33 mmHg)
• PAWP ≤15 mmHg (2 mmHg)
• PVR >3 Wood units (8.16 Wood units)

These values meet the criteria for pre-capillary pulmonary hypertension 1. The very low wedge pressure (2 mmHg) with elevated mPAP strongly suggests pulmonary arterial hypertension (Group 1 PH) or chronic thromboembolic pulmonary hypertension (Group 4 PH) rather than PH due to left heart disease 1.

Clinical Context

This hemodynamic profile is concerning and warrants further evaluation:

• The PVR of 8.16 Wood units is similar to values seen in patients with idiopathic pulmonary arterial hypertension or chronic thromboembolic pulmonary hypertension before treatment 1
• This level of PVR elevation is associated with right ventricular dysfunction and poor outcomes if left untreated 1
• The very low wedge pressure (2 mmHg) is unusual and may warrant confirmation, as typical PAWP values even in pre-capillary PH are often in the 8-12 mmHg range 1

Important Considerations

• Confirm accuracy of the wedge pressure measurement, as 2 mmHg is unusually low and could potentially represent a technical error
• Evaluate for potential causes of pre-capillary PH including connective tissue diseases, chronic thromboembolic disease, and idiopathic PAH 1
• Assess right ventricular function, as this level of PVR elevation places significant strain on the right ventricle 1
• Consider ventilation/perfusion scanning to rule out chronic thromboembolic pulmonary hypertension, which would be potentially surgically treatable 1

This PVR calculation provides critical information for diagnosis, risk stratification, and therapeutic decision-making in the management of pulmonary hypertension.