The pulmonary vascular resistance in newborns decreases to that of adults by which age?

The pulmonary vascular resistance in newborns decreases to that of adults by which age?

• A. 1 day
• B. 1 week
• C. 2 months
• D. 2 years

Answer: (C)

The main idea is how the pulmonary circulation switches from a high-resistance, fluid-filled state at birth to the low-resistance system needed for normal oxygenation. When a baby takes the first breaths, the lungs aerate, alveoli expand, and oxygen tension rises. This triggers vasodilation of the pulmonary arteries (with mediators like nitric oxide) and a reduction in the factors that kept the vessels constricted. Removal of the placental circulation also helps lower overall resistance. As the pulmonary vascular bed remodels and the baby’s circulation stabilizes, the pulmonary vascular resistance gradually declines toward adult values. By about two months of life, PVR has typically reached levels comparable to adults, which is why that timing is chosen. The earlier time points occur before full maturation of the pulmonary vasculature, and two years would be far beyond the normal maturation window.

The main idea is how the pulmonary circulation switches from a high-resistance, fluid-filled state at birth to the low-resistance system needed for normal oxygenation. When a baby takes the first breaths, the lungs aerate, alveoli expand, and oxygen tension rises. This triggers vasodilation of the pulmonary arteries (with mediators like nitric oxide) and a reduction in the factors that kept the vessels constricted. Removal of the placental circulation also helps lower overall resistance. As the pulmonary vascular bed remodels and the baby’s circulation stabilizes, the pulmonary vascular resistance gradually declines toward adult values. By about two months of life, PVR has typically reached levels comparable to adults, which is why that timing is chosen. The earlier time points occur before full maturation of the pulmonary vasculature, and two years would be far beyond the normal maturation window.