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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.
An uncorrected left-to-right shunt can progress to a right-to-left shunt; this process is termed Eisenmenger syndrome. [3] This is seen in Ventricular septal defect, Atrial septal defect, and patent ductus arteriosus, and can manifest as late as adult life. This switch in blood flow direction is precipitated by pulmonary hypertension due to ...
A cardiac shunt is when blood follows a pattern that deviates from the systemic circulation, i.e., from the body to the right atrium, down to the right ventricle, to the lungs, from the lungs to the left atrium, down to the left ventricle and then out of the heart back to the systemic circulation.
The right-to-left shunt is an abnormal blood circulation that enables deoxygenated blood to pass from the right side to the left side of the heart and skips the lungs. Thus, no oxygenation occurs, and reduced gas exchange results in hypoxemia as fresh oxygen cannot reach the shunted blood. [ 18 ]
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.
Cardiac shunts may be described as right-to-left, left-to-right or bidirectional, or as systemic-to-pulmonary or pulmonary-to-systemic.; Cerebral shunt: In cases of hydrocephalus and other conditions that cause chronic increased intracranial pressure, a one-way valve is used to drain excess cerebrospinal fluid from the brain and carry it to other parts of the body.
It is caused by structural defects of the heart such as right-to-left or bidirectional shunting, malposition of the great arteries, or any condition which increases pulmonary vascular resistance. The result may be the development of collateral circulation.
If left untreated, the disease may progress from left-to-right shunt (acyanotic heart) to right-to-left shunt (cyanotic heart), called Eisenmenger's syndrome. Pulmonary hypertension is a potential long-term outcome, which may require a heart and/or lung transplant. Another complication of PDA is intraventricular hemorrhage. [citation needed]