If you’re living with pulmonary hypertension (PH), you may be confused by the different terms used to describe it. One way PH can be categorized is as precapillary or postcapillary. These terms describe where the high blood pressure in the pulmonary arteries originates. Understanding pulmonary circulation is key to understanding where it can go wrong.

What is the difference between precapillary pulmonary hypertension and postcapillary pulmonary hypertension? What do these terms mean? This article will review four differences between precapillary PH and postcapillary PH. We’ll learn about different causes, how to find out which one it is, treatments for each kind, and how they affect people in the long run.

Pulmonary Circulation and PH

PH refers to high blood pressure in the arteries that bring blood from the heart to the lungs. These are also known as pulmonary arteries. This high blood pressure can come from different problems in the body.

Blood without oxygen flows from the right side of the heart to the lungs. In the lungs, it receives oxygen in small vessels called capillaries. The oxygenated blood then flows from the lungs to the left side of the heart. The circulation of blood from the right side of the heart to the lungs to the left side of the heart is known as the pulmonary circuit.

“Precapillary” means “before the capillaries” within the pulmonary circuit. Precapillary PH originates from problems in the pulmonary arteries.

“Postcapillary” means “after the capillaries” within the circuit. Postcapillary PH originates from problems in the left side of the heart.

Precapillary and postcapillary PH have many overlapping symptoms, including tiredness and shortness of breath. One myPHteam member with precapillary PH reported, “My biggest issue now is fatigue. I’m exhausted most of the time and sleep, sleep, sleep. I only get up for meals.”

A member with postcapillary PH shared, “I am so tired when I walk to the bathroom and back, my heart beats so hard I just collapse.”

Now that we’ve discussed some shared symptoms between precapillary and postcapillary PH, here are four key differences between them.

1. Precapillary and Postcapillary PH Have Different Causes

Precapillary and postcapillary PH originate from problems in different parts of the circulatory system.

Precapillary PH

Precapillary PH is caused by problems originating in the pulmonary arteries. The pulmonary arteries become stiff and narrow, leading to a buildup in pressure.

The World Health Organization (WHO) has five classifications of pulmonary hypertension based on the cause. Most individuals with precapillary PH are in either group 1 or group 4. Group 1 includes all types of pulmonary arterial hypertension (PAH).

PAH can be idiopathic, meaning its cause is unknown. Idiopathic pulmonary arterial hypertension (IPAH) — formerly known as primary pulmonary hypertension — is a common example of precapillary PH. PAH can also be caused by other factors such as HIV, genetics, or specific drugs. Congenital PAH — PAH you’re born with — is a type of precapillary PH.

Group 4 PH, also known as chronic thromboembolic pulmonary hypertension (CTEPH), is caused by chronic blood clotting that has traveled to the pulmonary arteries. The blood clots obstruct (block) arteries by narrowing them. This results in high blood pressure in the pulmonary arteries.

Postcapillary PH

Postcapillary PH is caused by left heart disease and medical problems in the left side of the heart. Some types of postcapillary PH are known as pulmonary venous hypertension (PVH). These cases are usually categorized by the WHO as group 2 PH.

Group 2 can include conditions such as left-sided valve disease, left-side ventricular heart failure, and mitral valve disease.

2. Right Heart Catheterization Can Help You Understand Your Diagnosis

Doctors use similar tests to diagnose precapillary and postcapillary PH. The major difference is what these tests find.

One test is called right heart catheterization. For this test, a small tube called a catheter will be inserted into your body to reach the right side of your heart. This is the best method to test the blood pressure of different parts of the heart and pulmonary arteries.

The test will take measurements — called hemodynamic measurements — and make calculations from those measurements. Certain cutoffs are used to determine if you have precapillary or postcapillary PH. They include:

• Mean pulmonary arterial pressure (mPAP)
• Pulmonary arterial wedge pressure (PAWP)
• Pulmonary vascular resistance (PVR)

An mPAP of greater than 20 millimeters of mercury (mm Hg) indicates any type of pulmonary hypertension.

The PAWP is an important measurement in differentiating between precapillary and postcapillary PH. This is because higher PAWP values indicate diastolic dysfunction, which is when the left heart is too rigid to properly fill with oxygenated blood.

Precapillary PH Criteria

Per the latest 2022 guidelines from the American Heart Association, the European Society of Cardiology, and the European Respiratory Society, criteria for diagnosing precapillary PH are as follows:

• mPAP greater than 20 mm Hg
• PAWP less than or equal to 15 mm Hg
• PVR greater than or equal to 2 Wood units

Your doctor may base (or may have based) your diagnosis on older guidelines from 2015, however, which are a little different.

Postcapillary PH Criteria

The criteria for diagnosing postcapillary PH under the latest guidelines are:

• mPAP greater than 20 mm Hg
• PAWP greater than 15 mm Hg
• PVR of 2 Wood units or fewer

Importantly, if the PAWP criteria match postcapillary PH, but the PVR is greater than 2 Wood units, the condition is called “combined pre- and postcapillary PH.”

3. Different Treatments Are Used for Precapillary and Postcapillary PH

Most treatments for PH were developed and tested for precapillary PH. These include:

• Phosphodiesterase 5 (PDE5) inhibitors — These drugs work with a molecule called nitric oxide to allow molecular pathways to be active for longer.
• Endothelin receptor antagonists — These bind to proteins in the pulmonary arteries and allow them to open.
• Prostacyclin analogs — These allow pulmonary arteries to open and prevent blood clots.

Additionally, health experts often recommend exercise therapy or precapillary PH.

On the other hand, treatment for postcapillary PH should target the underlying cause. Medication should treat left heart failure rather than pulmonary hypertension. While treatments for precapillary PH are often used to treat postcapillary PH, there isn’t research to support them as effective. Clinical trials are needed to determine if these medications are effective for postcapillary PH.

4. Prognosis May Vary Based on Condition

Is there a difference in the prognosis, or outcome, between precapillary and postcapillary PH? The prognosis of a condition is determined by many different factors. These include the characteristics (age, weight, sex) of each individual. Prognosis also depends on comorbidities — other medical conditions that may be present with PH.

For individuals with postcapillary PH, having the following comorbidities can affect their outcome:

• Chronic obstructive pulmonary disease (COPD) — A collection of progressive lung diseases
• Sleep apnea — A sleep disorder that causes individuals to stop breathing in their sleep

Prognosis can be assessed using different research criteria. One way is to see how many people survive after five years of treatment.

In a study from the Journal of the American College of Cardiology, the same amount of individuals with precapillary PH and postcapillary PH survived after five years. However, the study also found that people with IPAH were at a higher risk of dying from complications from their PH.

Speak With Your Doctor

It’s important to point out that the clinical classifications for precapillary and postcapillary PH have changed over time. Some individuals have met the criteria for one category and were then grouped differently following the change in criteria. Ultimately, having ongoing conversations with your doctor is the best practice. Based on your condition, they can recommend the best treatment and management strategies.

Talk With Others Who Understand

On myPHteam, the social network for people with pulmonary hypertension and their loved ones, more than 51,000 members come together to ask questions, give advice, and share their stories with others who understand life with pulmonary hypertension.

Do you have precapillary or postcapillary pulmonary hypertension? What has your experience been? Share your experience in the comments below, or start a conversation by posting on your Activities page.