A critical discussion of the recorded form of the fast vital capacity record.

If an individual inspires as deeply as he can and then expires his whole vital capacity as rapidly as he is able into a recording spirometer the resulting record is known as a fast vital capacity (F.V.C.) tracing, or, sometimes, as an expiratory vital spirogram (E.V.S.). Recently much attention has been given to the possibility of using this record as a basis for the prediction of the maximum ventilatory capacity (M.V.C.) of the same individual, and a number of papers have appeared (Roche and Thivollet, 1949; Tiffeneau, Bousser and Drutel, 1949; Gaensler, 1951 ; Kennedy, 1953) in which attempts have been made to correlate the slope of the F.V.C. record-or of some portion of it-with the M.V.C. Kennedy (1953) draws attention to the form of what he terms the E.V.S. tracing and comments that it is never uniform throughout its length, and may, except in certain types of abnormal patients, be divided into two fractions. The first fraction is relatively steep and linear. It then breaks away into a second fraction, which is less steep, and later the curve becomes undulatory. The position of the dividing point between the first and second fraction, i.e., where the tracing deviates from a straight line, has been termed the critical point (Kennedy, 1950)."