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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.
A ventilation perfusion scan or lung scintigraphy can be used to diagnose areas of lungs being ventilated but not adequately perfused. This results in a raised Alveolar-arterial (A-a) gradient which is responsive to supplemental oxygen. In conditions with right to left shunts, there are also ventilation perfusion defects with high A-a gradients.
Physiologic dead space cannot change as it is ventilation without perfusion. A shunt is a perfusion without ventilation within a lung region. [citation needed] Low tidal volume ventilation was the primary independent variable associated with reduced mortality in the NIH-sponsored ARDSNet trial of tidal volume in ARDS.
Platypnea–orthodeoxia syndrome is a rare medical condition in which a person has shortness of breath and low oxygen saturations when upright (platypnea and orthodeoxia), but no symptoms when lying down. It can be caused by ventilation-perfusion mismatch, intracardiac shunting, or pulmonary shunting. In some cases, the cause is multifactorial ...
Hypoxemia is caused by five categories of etiologies: hypoventilation, ventilation/perfusion mismatch, right-to-left shunt, diffusion impairment, and low PO 2. Low PO 2 and hypoventilation are associated with a normal alveolar–arterial gradient (A-a gradient) whereas the other categories are associated with an increased A-a gradient.
Ventilation–perfusion coupling is the relationship between ventilation and perfusion processes, which take place in the respiratory system and the cardiovascular system. [1] Ventilation is the movement of gas during breathing, and perfusion is the process of pulmonary blood circulation , which delivers oxygen to body tissues. [ 2 ]
By redirecting blood flow from poorly-ventilated lung regions to well-ventilated lung regions, HPV is thought to be the primary mechanism underlying ventilation/perfusion matching. [1] [2] The process might initially seem counterintuitive, as low oxygen levels might theoretically stimulate increased blood flow to the lungs to increase gas exchange.
Pulmonary shunts exist when there is normal perfusion to an alveolus, but ventilation fails to supply the perfused region. A portosystemic shunt (PSS), also known as a liver shunt, is a bypass of the liver by the body's circulatory system. It can be either a congenital or acquired condition.