Used a hot-wire anemometer sensor.  From Office Spirometry. A practical guide to the selection and use of spirometers.  By PL Enright and RE Hyatt.  Published by Lea and Febiger, 1987.  Page 115.

Given the push-button selectors for height, gender, race etc. , likely from the late 1980’s.  The flow sensor looks like a turbine.  Found on an Ebay listing.