Probably pneumotach-based. Found in A New Approach to Application of a Computer in Spirometry by A. Patel, D. Tashkin, G. Ellis and E. Peterson, published by Springer, 1980.
Tag Archives: Cavitron
Spirometer, Donti Pulmonary Performance Analyzer, 1974
Advertisement in Chest, vol 65, no 3, March 1974, page 356D.