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Pulmonary Perfusion Disorders

Perturbationes perfusionis pulmonum

For medical students2 min readUpdated 2026-10-10

Pulmonary perfusion disorders are associated with pathological changes in blood pressure within the pulmonary vascular bed. Key manifestations of these disorders include pulmonary hypertension and pulmonary hypotension, each characterized by distinct hemodynamic features and etiologies.

Pulmonary CirculationPerfusion pathology alters pressure within the pulmonary vessels.

HypertensionSustained elevation of blood pressure within the pulmonary vasculature.

Pre-capillary FormSystolic pressure > 30 mmHg, diastolic pressure > 12 mmHg.

HypotensionSustained reduction of blood pressure within the pulmonary circulation.

Main Forms and General Characteristics

Pulmonary perfusion pathology is manifested by deviations of blood pressure in the pulmonary circulation from normal values. In clinical practice, two opposite states are distinguished:

Pulmonary hypertension — sustained elevation of pressure.
Pulmonary hypotension — sustained decrease of pressure.

Each of these states develops under the influence of specific hemodynamic mechanisms affecting the microvasculature, the heart, or the total circulating blood volume.

Pulmonary Hypertension: Pre-capillary and Post-capillary Causes

Pulmonary hypertension is classified into three main forms: pre-capillary, post-capillary, and mixed.

Pre-capillary form is accompanied by increased pressure in the pre-capillaries and capillaries, where systolic values exceed 30 mmHg and diastolic values exceed 12 mmHg. The primary trigger here is smooth muscle spasm of the arterioles, which is provoked by stress, pulmonary embolism (PE), catecholamine release in pheochromocytoma, acidosis, and alveolar hypoxia (Euler-Liljestrand mechanism). Obstruction of microvessels by emboli or their compression by tumors and bronchial asthma can also be causative factors.
Post-capillary form is caused by impaired blood outflow into the left atrium, leading to an accumulation of excess blood in the lungs. This results from mitral stenosis, compression of the pulmonary veins by tumors or lymph nodes, and left ventricular heart failure.

Mixed Form and Pulmonary Hypotension

The mixed form of hypertension occurs as a complication and progression of pre- or post-capillary disorders. For example, impaired blood outflow into the left atrium triggers reflex vasoconstriction of the pulmonary arterioles. General manifestations of hypertension include hypoxemia, hypercapnia, acidosis, reduced vital capacity (VC), and signs of heart failure with congestion.

In contrast, pulmonary hypotension is characterized by a sustained drop in pressure within the pulmonary circulation. It is caused by congenital heart defects with right-to-left shunting of venous blood into the arterial bed (e.g., Tetralogy of Fallot), marked hypovolemia due to vomiting or shock, and systemic arterial hypotension during circulatory collapse and cardiac decompensation.

Mnemonic

Pulmonary hypertension has three main pillars: Pre (arteriolar spasm and hypoxia), Post (congestion due to the left atrium), and Mixed (their combination as the disease progresses).

Frequently asked questions

What is the pathogenesis of Kitaev's reflex in mitral stenosis?

The pathogenesis of Kitaev's reflex involves reflex vasospasm of the pulmonary arterioles. This process produces active (arterial) pulmonary hypertension, which acts as a compensatory mechanism to protect capillaries from edema. The vasospasm develops in response to transmitted elevated pressure from the left atrium into the pulmonary veins and capillaries (so-called passive venous hypertension resulting from impaired blood flow in mitral stenosis).

What is the molecular mechanism of hypoxic pulmonary vasoconstriction (the Euler-Liljestrand reflex)?

The mechanism of the Euler-Liljestrand reflex is triggered by an acute decrease in the partial pressure of oxygen in inspired air (alveolar hypoxia), which causes spasm of the smooth muscle cells in the walls of pulmonary arterioles.

The pathogenesis involves the production of vasoconstrictive mediators, including:

Catecholamines;
Endothelin;
Thromboxane A2.

Aside from Tetralogy of Fallot, what other heart defects lead to pulmonary hypotension due to right-to-left shunting?

In addition to Tetralogy of Fallot, pulmonary valve regurgitation leads to pulmonary hypotension due to right-to-left shunting. In such heart defects, venous blood is directed straight into the arterial system, causing a sustained decrease in blood pressure within the pulmonary circulation.

What criteria define pre-capillary pulmonary hypertension?

The condition is diagnosed when pressure increases in the pre-capillaries and capillaries, with systolic pressure exceeding 30 mmHg and diastolic pressure exceeding 12 mmHg.

What are the main causes of the post-capillary form of pulmonary hypertension?

This form develops due to impaired blood outflow into the left atrium. The main causes include mitral stenosis, compression of the pulmonary veins by lymph nodes or tumors, and left ventricular heart failure.

What causes pulmonary hypotension?

A drop in pulmonary circulation pressure is caused by congenital heart defects with right-to-left shunting (Tetralogy of Fallot), hypovolemia during shock or diarrhea, as well as systemic arterial hypotension and collapse.

Go deeper

The Euler-Liljestrand reflex and mechanisms of alveolar hypoxia
The role of endothelin and thromboxane A2 in pulmonary vasoconstriction
Pathogenesis of respiratory and mixed acidosis in chronic hypertension
Hemodynamic consequences of right-to-left blood shunting in congenital heart defects
Impact of left and right ventricular failure on the pulmonary circulation