State of the Art
Immediately after birth, the pulmonary vasculature is remodeled rapidly to effect an abrupt reduction in pulmonary vascular resistance. Remodeling continues rapidly for the first 1-2 months, as the lung adapts to extrauterine life, and then more slowly as the vessels grow throughout childhood. Little is known about normal early postnatal development, yet failure to remodel in the presence of an anatomically normal heart leads to persistent (idiopathic) pulmonary hypertension. In children with congenital heart disease, abnormal remodeling may lead eventually to pulmonary vascular disease, and also alters pulmonary vascular reactivity and the response to pharmacologic agents. We review current concepts of pulmonary vascular remodeling in early postnatal life, emphasizing the normal. Changes in form and (unction in the pulmonary arteries of the intact animal and man are discussed in relation to changes in form and function described in experimental studies of isolated vessels and cultured endothelial and smooth muscle cells.
Normal Postnatal Pulmonary Arterial Development
Normal postnatal pulmonary arterial development can be divided into three overlapping stages: stage 1, adaptation to extrauterine life, lasting from birth until approximately 4 days of age; stage 2, structural stabilization, beginning at birth but becoming more evident by 4 days and lasting until 3-4 weeks of age; and stage 3 growth, which continues until adulthood. More info
Stage 1: Adaptation to Extrauterine LAfe
Adaptation involves the entire arterial pathway, the elastic and large muscular conducting arteries in addition to the resistance arteries just proximal to the respiratory unit. The different segments of the pathways behave in a closely integrated manner. Hie earliest and most dramatic changes, however, are seen in the precapillary arteries. Tliese vessels consist of only endothelial cells, surrounded by pericytes. At birth, the endothelial cells are squat, have a narrow base on the subendothelium, a low surface/volume ratio, and many surface projections (Fig 1). There is considerable overlap of adjacent lateral cell borders, with interdigitating contacts containing patches of gap and tight junctions. Five minutes after birth, the endothelial cells have become thinner and gradually show less cell/cell overlap. The surface/ volume ratio increases, and few if any surface projections are seen, presumably because they afforded the surface membrane material necessary to allow the cells to “spread” so rapidly.
Figure 1. Shape changes in the endothelial cells of precapillary arteries during the first 3 weeks of life, a-c suggest stretching during inflation; d-e, spreading during dilatation.
Category: Pulmonary Hypertension
Tags: pulmonary hypertension, pulmonary vascular, smooth muscle