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The Proportion of Lung Vessels Blocked by Albumin Microspheres

Queen Elizabeth Medical Centre, Edgbaston, Birmingham, England

Correspondence: For reprints contact: L. K. Harding, Nuclear Medicine, Dudley Road (Birmingham) Hospital, Birmingham 18, England.

ABSTRACT

The number and diameter of vessels in the pulmonary circulation have been determined from a resin cast of a human lung. Assuming that microsphres (A) have a density of 1 gm/cc; (B) are perfectly spherical; (C) are of uniform diameter; and (D) will each block only one vessel—the percentage of pulmonary vessels blocked by 1 mg of albumin has been calculated. Spheres 60–90 µm in diameter block 0.31% of vessels, whereas smaller spheres 0.15 µm in diameter block 0.14%. Very large particles (525 µm) block only 0.12% of the pulmonary circulation, which suggests that they would not be more damaging than smaller spheres unless they produced another effect such as spasm in adjacent vessels. These results are in keeping with the clinical safety of lung scanning.