The spatial-temporal redistribution of pulmonary blood flow with postnatal growth.

The pulmonary vascular tree undergoes remarkable postnatal development and remodeling. While a number of studies have characterized longitudinal changes in vascular function with growth, none have explored regional patterns of vascular remodeling. We therefore studied six neonatal pigs to see how regional blood flow changes with growth. We selected pigs because of their rapid growth and their similarities to human development with respect to the pulmonary vascular tree. Fluorescent microspheres of varying colors were injected into the pulmonary circulation to mark regional blood on days 3, 12, 27, 43, and 71 after birth. The animals were awake and in the prone posture for all injections. The lungs were subsequently removed, air dried, and sectioned into approximately 2-cm(3) pieces. Flow on each injection day was determined for each piece. Despite the increase in the hydrostatic gradient in the lung with growth, there was a strong correlation between blood flow to the same lung piece when compared on days 3 and 71 (0.73 +/- 0.12). Although a dorsal-ventral gradient of perfusion did not exist on day 3, blood flow increased more in the dorsal region by day 12 and then gradually became more uniform by day 71. Although most of the lung pieces did not show any discernable pattern of blood flow redistribution, there were spatial patterns of blood flow redistribution that were similar across animals. Our findings suggest that local mechanisms, shared across animals, guide regional changes in vascular resistance or vasoregulation during postnatal development. In the pig, these mechanisms act to produce more uniform flow in the normal posture for an ambulating quadruped. The stimuli for these changes have not yet been identified.