Pulmonary arterial tree: growth of the tunica media during the first ten years of life.

The developmental changes in the tunica media of the pulmonary trunk and left and right pulmonary arteries were studied in 51 hearts and the great vessels of infants and children up to the age of ten years who died from non-vascular diseases. The internal diameters of the pulmonary arterial tree were measured together with the thickness of the tunica media and the packing density of its elastic fibres. In spite of the age-related (about sixfold) increase in the internal diameters of the vessels there were no parallel significant changes in the characteristics of their tunica media. Furthermore, the configuration of the elastic fibres showed no clear age-related changes in any of the vessels. In conclusion the structure of the wall of the pulmonary trunk and of the pulmonary arteries, although different in embryological origin, seems to show the same pattern of growth during bodily development, with absence of significant correlations between the internal diameters on the one hand and media thickness and packing densities of the elastic fibres on the other. This is possibly the result of the low pulmonary blood pressure.