[Estimation of configuration of F-V curve with tangent time constant and mechanism involved].
The tangent time constants (tau t) of high, middle and low lung volumes tau t75, tau t50 and tau t25 were calculated with IBM PC/XT computer from the maximal expiratory flow volume (MEFV or F-V) curves of 1270 normal adolescent, middle-aged and old persons (age from 6 to 79). In the adolescents magnitude of tau t75 > 1s, and tau t75 > tau t50 > tau t25 reflected that the F-V curve had a round top and concaved towards the volume axis. In the old persons magnitude of tau t75 < 1s and tau t75 > tau t50 < tau t25 caused the curve to have a peak-shape top with its tail convex to the volume axis. In the middle-aged persons the indices were found to be intermediate between the adolescent and old persons. The configuration of F-V curve reflected by tau t was correspondent to that reflected with slope ratio (SR) by mead. The appearance of the peak-shape top on the F-V curve in the old persons was due to the reduced elasticity and increased collapsibility of the central airway. According to the wave-speed theory, the choke point (CP) occurs firstly at the least cross-sectional area of the collapsed trachea, then V75 is limited and decreases rapidly, and makes tau t75 < 1, so that a peak-shape top is developed on the F-V curve. The convex of the tail of F-V curve to the volume axis in the old persons is chiefly due to the reduced supporting force to the small airways and the decrease in the lung elastic recoil with aging. This leads to an increase in resistance and decrease in V25. Therefore, V25 can only descend slowly to the zero at RV, and tau t25 is elongated, so that the tail of the F-V curve is convex to the volume axis.
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D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D005260:Female; D006801:Humans; D008168:Lung / Q000502:physiology*; D008297:Male; D008449:Maximal Expiratory Flow-Volume Curves; D008838:Microcomputers; D008875:Middle Aged