Pulmonary Hypertension

Pulmonary hypertension is a haemodynamic state of abnormally elevated blood pressure in the pulmonary arteries, defined by a raised mean pulmonary arterial pressure measured at right-heart catheterisation. It is not a single disease but a final common pathway reached by many conditions, and its central consequence is a progressively increased load on the right ventricle.

Definition

Pulmonary hypertension is defined haemodynamically by an elevated mean pulmonary arterial pressure at rest, assessed by right-heart catheterisation; pre-capillary and post-capillary forms are distinguished using pulmonary vascular resistance and pulmonary arterial wedge pressure (Simonneau, 2019; Humbert, 2022).

Scope

This topic covers the haemodynamic definition of pulmonary hypertension, the distinction between pre-capillary and post-capillary patterns, the clinical classification into broad groups by mechanism, and the right-ventricular consequences of chronic pressure elevation. It is a reference account of how the condition is defined and categorised, not a guide to its management.

Core questions

• How is pulmonary hypertension defined haemodynamically, and how has the threshold changed?
• What separates pre-capillary from post-capillary pulmonary hypertension?
• How are the clinical groups of pulmonary hypertension organised by mechanism?
• Why does chronic pressure elevation lead to right-ventricular failure?

Key concepts

• Mean pulmonary arterial pressure
• Pulmonary vascular resistance
• Pulmonary arterial wedge pressure
• Pre-capillary versus post-capillary pattern
• Clinical classification into groups by mechanism
• Pulmonary vascular remodelling
• Right-ventricular afterload and failure

Mechanisms

Pulmonary hypertension arises when the pulmonary vascular bed offers increased resistance to flow or when pressure is transmitted backward from the left heart. In pre-capillary disease, remodelling and constriction of small pulmonary arteries raise resistance while the wedge pressure remains low; in post-capillary disease, elevated left-heart filling pressures raise pulmonary pressure passively. The updated framework lowered the defining threshold for mean pulmonary arterial pressure and incorporated pulmonary vascular resistance to better identify pre-capillary disease (Simonneau, 2019). Whatever the cause, sustained elevation increases right-ventricular afterload, driving hypertrophy and, ultimately, right-ventricular failure (Humbert, 2022).

Clinical relevance

Pulmonary hypertension is recognised when symptoms such as exertional breathlessness are coupled with signs of raised pulmonary pressure and right-heart strain, confirmed by haemodynamic measurement. Distinguishing its groups matters because they reflect very different underlying processes. This entry describes how the condition is defined and classified and is not a basis for individual diagnosis or treatment.

Epidemiology

Pulmonary hypertension as a haemodynamic finding is relatively common because it complicates frequent conditions such as left-heart disease and chronic lung disease, whereas pulmonary arterial hypertension (the pre-capillary group of primarily vascular origin) is uncommon. Precise population estimates vary by group and definition (Humbert, 2022).

Evidence & guidelines

The current haemodynamic definition and clinical classification derive from the updated expert framework (Simonneau, 2019) and the 2022 ESC/ERS guideline (Humbert, 2022); both are cited here for definition and classification rather than as care directives.

History

Pulmonary hypertension was first understood through the haemodynamic measurements made possible by right-heart catheterisation, and successive expert meetings progressively refined its definition and grouped the disorders by mechanism. A notable recent development is the lowering of the mean pulmonary arterial pressure threshold and the formal use of pulmonary vascular resistance to define pre-capillary disease (Simonneau, 2019).

Debates

Where should the haemodynamic threshold for pulmonary hypertension be set?

The defining threshold for mean pulmonary arterial pressure was lowered in the updated framework, raising discussion about how to interpret and act on mildly elevated values that fall above the new but below the older cut-off.

Key figures

• Gerald Simonneau
• Marc Humbert

Seminal works

• simonneau-2019
• humbert-2022

Frequently asked questions

Is pulmonary hypertension the same as systemic high blood pressure?

No. It refers specifically to elevated pressure in the pulmonary arteries that supply the lungs, measured at right-heart catheterisation, and is distinct from systemic arterial hypertension.

What is the difference between pre-capillary and post-capillary pulmonary hypertension?

Pre-capillary disease reflects increased resistance within the pulmonary arteries themselves with a low wedge pressure, whereas post-capillary disease reflects pressure transmitted backward from the left side of the heart.