Technique for making hollow central airway casts.

We have developed a method for producing rigid hollow casts of the central airways. Woods metal (melting point 70 degrees C) was poured into the airways at the trachea of an excised canine lung air-dried at a transpulmonary pressure of 30 cmH2O. The tissue was dissolved and removed, and the resulting negative cast was carefully trimmed leaving only airways with a diameter of 2 mm or greater. The cast was then electroplated with copper that provided a rigid jacket encasing the Woods metal. Heating this structure to 100 degrees C liquefied the Woods metal allowing the majority of it to flow out. Residual amounts were readily removed by a high-pressure steam hose attached to the trachea. Comparisons were made between airway diameters from in vivo radiographic bronchograms (DB) and direct measurements of the resulting trimmed Woods metal cast (DC). Linear regression analysis of these data indicated a high degree of correlation (DC = 0.98 DB + 0.03, r = 0.99). We concluded that this technique produces positive casts which provide a good representative model of the central airways.