Hypoxic pulmonary vasoconstriction

Hypoxic Pulmonary Vasoconstriction

File:Hypoxic pulmonary vasoconstriction.jpg

Illustration of Hypoxic Pulmonary Vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV), also known as Euler-Liljestrand mechanism, is a physiological phenomenon in which the pulmonary arteries constrict in the presence of hypoxia (low oxygen levels) without hypercapnia (increased carbon dioxide levels), thereby diverting blood flow to alveoli with a higher oxygen content.

Mechanism

The exact mechanism of HPV is not fully understood, but it is believed to involve the direct effect of oxygen on vascular smooth muscle. In conditions of low oxygen, pulmonary vascular smooth muscle contracts, leading to vasoconstriction. This response is unique to the pulmonary circulation; in most tissues, hypoxia leads to vasodilation.

Clinical Significance

HPV has important clinical implications. It is a major factor in maintaining optimal gas exchange in the lungs, particularly in diseases such as chronic obstructive pulmonary disease (COPD) and acute respiratory distress syndrome (ARDS). However, it can also contribute to pulmonary hypertension in conditions of chronic hypoxia.

Inhibition and Enhancement

Several factors can inhibit or enhance HPV. For example, certain drugs, such as calcium channel blockers and nitric oxide, can inhibit HPV. On the other hand, factors such as acidosis and hypercapnia can enhance HPV.

See Also

• Pulmonary hypertension
• Pulmonary circulation
• Vasoconstriction