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Summary The normal pulmonary arterial vascular bed undergoes a morphological development during infancy. The intrapulmonary arteries at birth have narrow luminae and thick vessel walls, thus resembling the structure of systemic arteries. During the first months of life, there is a progressive change, so that the lumen of the intrapulmonary arteries widens and the thickness of the vessel wall decreases. After 3–4 months of age, this development takes place more slowly, and after 8 months of life has almost subsided. In regard to the different types of intrapulmonary vessels, the elastic arteries (intrapulmonary arteries of greater size) seem to undergo an earlier development than the muscular arteries (smaller type of intrapulmonary arteries). Corresponding to the progressive vascular change during the first months of life, the hemodynamic behaviour of the pulmonary circulation changes from the high‐resistance circulation of the fetus to the low‐resistance circulation seen in the adult.

SummaryThe normal pulmonary arterial vascular bed undergoes a morphological development during infancy. The intrapulmonary arteries a t birth have narrow luminae and thick vessel walls, thus resembling the structure of systemic arteries. During the first months of life, there is a progressive change, so that the lumen of the intrapulmonary arteries widens and the thickness of the vessel wall decreases.After 3‐4 months of age, this development takes place more slowly, and after 8 months of life has almost subsided. In regard to the different types of intrapulmonary vessels, the elastic arteries (intrapulmonary arteries of greater size) seem to undergo an earlier development than the muscular arteries (smaller type of intrapulmonary arteries). Corresponding to the progressive vascular change during the first months of life, the hemodynamic behaviour of the pulmonary circulation changes from the high‐resistance circulation of the fetus to the low‐resistance circulation seen in the adult.

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