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The Shunt equation (also known as the Berggren equation) quantifies the extent to which venous blood bypasses oxygenation in the capillaries of the lung.. “Shunt” and “dead space“ are terms used to describe conditions where either blood flow or ventilation do not interact with each other in the lung, as they should for efficient gas exchange to take place.
An area with ventilation but no perfusion (and thus a V/Q undefined though approaching infinity) is termed "dead space". [6] Of note, few conditions constitute "pure" shunt or dead space as they would be incompatible with life, and thus the term V/Q mismatch is more appropriate for conditions in between these two extremes.
Alveolar dead space and insufficient perfusion result in a V/Q ratio above 0.8 with decreased fresh oxygen in the alveoli. [1] This might have been caused by blood clotting, heart failure, pulmonary emphysema, or damage in alveolar capillaries. [12] Diagram of pulmonary shunt in alveoli and pulmonary capillary
A pulmonary shunt is the passage of deoxygenated blood from the right side of the heart to the left without participation in gas exchange in the pulmonary capillaries. It is a pathological condition that results when the alveoli of parts of the lungs are perfused with blood as normal, but ventilation (the supply of air) fails to supply the perfused region.
Total dead space (also known as physiological dead space) is the sum of the anatomical dead space and the alveolar dead space. Benefits do accrue to a seemingly wasteful design for ventilation that includes dead space. [1] Carbon dioxide is retained, making a bicarbonate-buffered blood and interstitium possible.
Hypoxic pulmonary vasoconstriction (HPV), also known as the Euler–Liljestrand mechanism, is a physiological phenomenon in which small pulmonary arteries constrict in the presence of alveolar hypoxia (low oxygen levels).
Mechanical dead space is another important parameter in ventilator design and function, and is defined as the volume of gas breathed again as the result of use in a mechanical device. Image of endotracheal tube placement required to connect a patient's physiologic airway to the ventilator.
It is generally only observed when a person is ventilated with positive pressure or hemorrhage. In these circumstances, blood vessels can become completely collapsed by alveolar pressure (PA) and blood does not flow through these regions. They become alveolar dead space. Zone 2 is the part of the lungs about 3 cm above the heart.