Before birth pulmonary vascular resistance is greater than systemic resistance because the

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Before birth pulmonary vascular resistance is greater than systemic resistance because the

In fetal life, the lungs are not used for gas exchange and remain fluid-filled and collapsed, so the vessels of the pulmonary circulation stay constricted. This lack of inflation and low oxygen tension in the lungs cause the pulmonary arteries to maintain high resistance, making the pulmonary vascular resistance greater than the systemic resistance. Because the lungs aren’t aerated, most blood bypasses them through the fetal shunts, which is exactly what keeps PVR high relative to SVR. After birth, lung inflation and increased oxygenation relax the pulmonary vessels, lowering PVR and shifting circulation toward the lungs.

In fetal life, the lungs are not used for gas exchange and remain fluid-filled and collapsed, so the vessels of the pulmonary circulation stay constricted. This lack of inflation and low oxygen tension in the lungs cause the pulmonary arteries to maintain high resistance, making the pulmonary vascular resistance greater than the systemic resistance. Because the lungs aren’t aerated, most blood bypasses them through the fetal shunts, which is exactly what keeps PVR high relative to SVR. After birth, lung inflation and increased oxygenation relax the pulmonary vessels, lowering PVR and shifting circulation toward the lungs.

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