From: The response of cardio-vascular system to respiratory exertion. HF Frost, The Boston Medical and Surgical Journal, 1924, page 109.
“The apparatus finally decided upon consists of two elements: a vacuum-pressure Tycos guage and a Simplex spirometer. The gauge is necessarily delicate, registering positive and negative pressure in centimeters of mercury. It is manufactured by the Taylor Instruments Companies of Rochester, New York. The spirometer is of the “wind-wheel” type, the revolutions of the wheel registering on the dial the amount of air expired, in cubic inches. It is manufactured by Messrs. Roberts and Quinn, 401 Bridge Street, Brooklyn, New York. We recognize that this type of spirometer does not accurately register vital capacity. A certain amount of air is “lost” in overcoming the inertia of the mechanism at the beginning of respiration; while after respiration has ceased the wheel continues to revolve for a short period until its momentum has ceased. To a certain extent, the latter fault compensates for the former. This type, however, suits our purpose in that it is compact, gives a sufficiently accurate idea of the vital capacity and offers considerable resistance to forced expiration.”