Body processes

Euler-Liljestrand Mechanism – Function, Task & Diseases

Euler-Liljestrand mechanism

When there is an insufficient supply of oxygen , the Euler-Liljestrand mechanism causes the vascular muscles in the lungs to contract , which improves the ventilation-perfusion quotient of the lungs . The mechanism is a natural reflex that only affects the lungs. The Euler-Liljestrand mechanism is pathological at high altitudes, for example, where it promotes pulmonary edema .

What is the Euler-Liljestrand mechanism?

During vasoconstriction , the blood vessels constrict . This narrows the vascular cross-section and changes the blood pressure . The smooth vascular muscles are responsible for vasoconstriction and, if necessary, also relax and thus dilate the vessels with vasodilation . The state of tension of the vascular muscles is mediated by various substances, for example by so-called vasoconstrictors in vasoconstriction.

A reflex vasoconstriction characterizes the Euler-Liljestrand mechanism. This natural bodily process occurs during hypoxia , i.e. when there is insufficient oxygen supply to the tissue . Both global and local hypoxia can trigger the Euler-Liljestrand reflex and thus cause a hypoxic pulmonary vasoconstriction or hypoxic pulmonary vascular response. The airway resistance increases locally as a result of the reflex.

The vasoconstriction as part of the Euler-Liljestrand mechanism only affects the pulmonary vascular system. In all other vessels of the body, hypoxia causes vasodilation. So as the pulmonary system contracts, all other vessels dilate to allow more oxygen-carrying blood to pass through.

function & task

The flow of blood through the lungs is localized. The same applies to the degree of lung ventilation. The lung tissue is locally ventilated and perfused differently. Due to physical relationships, such as gravity, the blood flow is higher in the basal parts, so that the basal lung has better blood circulation . Because the basal lung areas are also less stretched, ventilation in these areas is also at a higher level. The apical parts of the lung are therefore poorly perfused and ventilated in direct comparison to the basal areas. 

Blood flow in particular decreases extremely from basal to apical. The ventilation also decreases, but compared to perfusion, the decrease in ventilation in the apical direction is much less. The ventilation-perfusion quotient indicates the ratio of lung ventilation to lung perfusion and thus cardiac output . Due to the local differences in the basal and apical parts, the apical ventilation-perfusion quotient is greater than one. In contrast, the basal ventilation-perfusion quotient is less than one. The optimal ventilation-perfusion ratio is again one. This ratio is not reached due to the local differences. The oxygen uptake of the blood therefore does not correspond to the absolute optimum.

Naturally, the perfusion and ventilation differences in the individual lung areas mean that blood fractions, such as the intrapulmonary right-to-left shunt, are not supplied with oxygen. To resolve this relationship, the Euler-Liljestrand mechanism reduces the affected shunts.

The reflex adapts the perfusion of the lungs to the ventilation in the relevant areas and thus improves the ventilation-perfusion quotient. The Euler-Liljestrand reflex achieves this goal with a contraction of the vascular musculature in the pulmonary vascular system, as mediated by insufficient oxygen supply.

In the case of ventilation disorders as part of pneumonia , for example, the vasoconstriction redistributes the blood through the Euler-Liljestrand mechanism. In this case, poorly ventilated sections receive less blood flow than better ventilated areas. In case of doubt, this effect is relevant for maintaining the oxygen supply in individual tissues and results in a redistribution of the blood.

Diseases & Ailments

The Euler-Liljestrand mechanism is a natural reflex, but in certain contexts it also has negative consequences for human health. This applies, for example, to the development of pulmonary hypertension in the context of chronic obstructive bronchitis or bronchial asthma . The Euler-Liljestrand reflex is significantly involved in the development of this pathological increase in vascular resistance and blood pressure in the pulmonary circulation . The vasoconstriction mediated by the reflex increases the afterload of the right heart and at the same time creates a ventricular pressure load. the heartresponds with compensation. As a result, concentric hypertrophy occurs in the right ventricle. This tissue enlargement of the right ventricle can result in right heart failure . With this phenomenon, the right heart no longer has sufficient pump capacity to pump enough blood back into the bloodstream . 

Another disease phenomenon related to the Euler-Liljestrand mechanism is pulmonary edema of altitude sickness . Mountaineers who move at altitudes of more than 2000 meters above sea level suffer from altitude sickness. The disease is an adaptation disorder of the organism, which results in functional disorders of the body. Athletes who start the ascent at high speed and have not previously acclimatised themselves are particularly at risk. One of the first symptoms of altitude sickness is retinopathy , in which the blood vessels in the retina protrude, causing progressive loss of vision.

Pulmonary edema occurs only with acute altitude sickness and is caused by the hypoxic vasoconstriction that the Euler-Liljestrand reflex results in. The increase in perfusion pressure during exertion at high altitudes leads to high-altitude pulmonary edema, because fluid from the vessels of the lungs increasingly enters the alveolar space. Altitude pulmonary edema is associated with acute danger to life and should be clarified and treated immediately in case of doubt. Ideally, high-altitude climbers turn back with retinopathy and start the descent or at least stay at the current altitude for acclimatization in order to prevent the development of pulmonary edema.

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.