PVR Calculator | Pulmonary Vascular Resistance Calculator

PVR calculator helps to evaluate the patient pulmonary vascular resistance. PVR is a diagnostic tool to evaluate pulmonary hypertension and its drastic effects on the human heart. In addition, this also serves the function to assess the underlying causes of any irregularity in the physiology of the lungs and heart. So indirectly, the PVR calculator helps to determine the level of pulmonary hypertension and their effects on normal heart functions.

This article is all about the pulmonary vascular resistance or PVR calculator and the normal quantitative ranges of PVR. In this way, it also helps you understand the clinical use of PVR and also the use of the PVR calculator in clinical practice. Continue reading the article to enhance your basic concepts regarding the PVR calculator.

What do you understand by the term pulmonary vascular resistance?

Pulmonary vascular resistance or PVR explains any vascular changes in the arteries associated with the lungs. It indicates any change in the blood-transporting arteries of the lungs. This type of circulation falls under the category of pulmonary circulation. In pulmonary circulation, the deoxygenated blood from the right ventricle moves toward the pulmonary arteries to get oxygenated by the lungs. After perfusion, the oxygenated blood moves from the lungs to the left atrium through pulmonary veins.

If the pressure in the pulmonary veins and arteries is too high, this condition is known as pulmonary hypertension. Due to this, the right ventricle has to pump more aggressively to reduce the pressure levels. It may cause right ventricle dilation. As a result, the right ventricle undergoes hyperplastic changes and grows in size. Due to the larger size, more power is generated by the right ventricle, leading to right ventricular dysfunction and, ultimately, failure. These consequences lead to decreased survival rates of the patients.

What are the normal values of pulmonary vascular resistance?

Pulmonary vascular resistance assesses vascular resistance in pulmonary circulation. It depends on three factors that are also variable. These basic factors are as follows:

• Arterial pressure
• Atrial pressure
• Pulmonary blood flow

Variables	Measuring units	Details	Normal value range
Mean pulmonary arterial pressure:	mmHg, kPa, psi, atm or cmH2O	Input to the pulmonary circulation	10 to 20 mmHg
Left atrial pressure:	mmHg, kPa, psi, atm or cmH2O	Output of the pulmonary circulation at the point where blood is expelled to the left atrium	6 to 12 mmHg
Pulmonary flow:	L/min, mL/min	In several cases, pulmonary blood flow is almost equal to cardiac output.	4 to 8 L/min

Considering all these values, the normal value of PVR ranges from 100 to 200 dynes×second/cm³ or Wood’s unit. Commonly, we consider PVR as 200 WU as a normal value.

What are the conditions that can lower the PVR range?

There are multiple conditions that can decrease the PVR’s normal range. These are as follows:

• Drugs including vasodilators – these drugs can reduce both the pulmonary and peripheral resistance
• Alkalemia or high blood pH can also decrease the overall pulmonary vascular resistance
• Hypocapnia or decreases PaCO2
• Multiple exercises have the potential to reduce pulmonary vascular resistance.

What are the common reasons that can enhance pulmonary vascular resistance?

In contrast to the PVR lowering factors, there are several other factors that can enhance pulmonary vascular resistance and ultimately pulmonary hypertension. These factors are as follows:

• Drugs that contain vasoconstrictor agents
• Hypoxemia or low PaCO2 level
• Hypercapnia or increased PaCO2 levels
• Low pH levels of blood or acidemia
• Pulmonary embolism
• Atelectasis which is the collapse of lungs due to reduced oxygen exchange

What is the basic formula used for a PVR calculator?

The PVR calculator formula is based on the three variables we mentioned in the above section. You need to know the values of these three variables to assess PVR. The formula for the PVR calculator is as follows:

PVR = 80 × (mean pulmonary arterial pressure – left atrial pressure) / cardiac output

Mean arterial pressure is measured in standard mmHg units.

Left atrial pressure is measured in standard mmHg units.

Cardiac output is measured in L/min

The ultimate result comes in measuring units of dynes×sec/cm³, which ar also known as Wood units.

How can we use the PVR calculator formula in normal clinical practice?

It is not as difficult to use a PVR calculator in clinical practice. You just need to know the pressure values to determine the PVR range. Let us take an example to simplify the use of the PVR calculator in normal practice.

For example, a patient visits your clinic and you suspect right heart failure. You want to know the pulmonary vascular resistance value to confirm your diagnosis. His other clinical parameters are as follows:

• Mean pulmonary arterial pressure = 24mmHg
• Left atrial pressure = -2mmHg
• Cardiac output = 7 L/min

Put all these values in the formula to evaluate PVR.

PVR = 80 × (mean pulmonary arterial pressure – left atrial pressure) / cardiac output

PVR = 80 × (24 mmHg – 2mmHg) / 7 L/min

PVR = 251.4 WU

The results indicate an increased pulmonary vascular resistance which explains a clear irregularity in his pulmonary and circulatory capacity. For this reason, the patient is already under the effects of pulmonary hypertension on the heart.

Conclusion

The PVR calculator is specified for the assessment of pulmonary vascular resistance. Pulmonary vascular resistance indirectly explains pulmonary hypertension. Pulmonary hypertension is mainly due to increased pressure in the pulmonary vessels. This increased pressure is fatal as it may lead to right heart failure. Therefore, physicians consider it an important tool to evaluate PVR and indirectly the consequences of pulmonary hypertension.

Frequently asked questions (FAQs)