Morphometry of the Small Pulmonary Arteries in Man

From a resin cast of a normal pulmonary arterial tree, the diameter, length, and number of branches in each order were determined for arteries from 25 to 300 μm in diameter. Histological sections 120-ftm thick were cut from a normal human lung in which the pulmonary artery had been injected with a mixture of ink and gelatin. Similar measurements were made on arteries from 10 to 70 ftm in diameter, and the mode of origin of the capillaries was studied. The data thus obtained were found to correspond reasonably well to values previously estimated by extrapolation from data for arteries of 100 (im or more in diameter. The branching rules apply down to arteries of about 10-15 μ in diameter, the estimated number of which is 73 million. Distal to these vessels, capillaries arise either directly from small arteries or indirectly via precapillaries which are given off in great numbers and diverse patterns from the small arteries.