A computerized approach to closing volume determination

A computer program was designed to analyze the single-breath nitrogen curve and calculate closing volume. The program solved simultaneously the two regression equations of phases III and IV with the intersection representing the point of closing volume. Thirty volunteers were asked to perform three consecutive single-breath nitrogen tests, all administered by an experienced laboratory technician. The tracings were also analyzed independently by two experienced observers. Correlation between visual and computer determination was excellent (r = 0.84), indicating that the computer method is as accurate in its closing volume analysis as is the present day method of visual determination. The results of this study suggest that widespread use of such a program could prove timesaving and eliminate the problems of interobserver and intraobserver variation, which presently impair the reliability of the SB N2 test.