Caliber and elastin content of the pulmonary trunk.

Internal diameter, thickness of media, and surface density of elastin in media of both pulmonary trunk and aorta were determined in a random group of 100 adults. Because of contrasting results of histologic vs chemical studies of the amount of elastin in the pulmonary trunk, we have used a television image analyzer for objective determination of surface density of elastin in histologic slides, applying the same method to the aorta for comparison. Both caliber and medial thickness of the pulmonary trunk increase somewhat with age. The surface density of elastin in the pulmonary trunk is not influenced by age and averages approximately 26%, with considerable individual variation. In patients with pulmonary hypertension, this percentage is consistently higher. We conclude that the decrease in extensibility of the aging pulmonary trunk is caused by changes in physical properties of the constituents of its wall, rather than by a decreasing elastin content.