Pitfalls of spirometry.

Abstract

Many spirograms cannot be interpreted properly even when the technician is expert. The criteria of an interpretable spirogram are (1) full inspiration, (2) quick attainment of highest flow, (3) continuous decrease in flow with expiration, (4) smooth, gradual termination, and (5) expiration lasting three seconds or more. Violation of these criteria leads to "pseudo-obstruction" when expiration is not forceful, to "concealed obstruction" when the graphic record is started late and to two kinds of "pseudo-restriction," one due to inadequate inspiration and the other to premature termination of expiration. A "decision tree" for dealing with large volumes of spirometric data is presented.