用切线时间常数和波速学说分析青少年F—V曲线形状形态的机理

Mechanism for the formation of F-V curve configuration analysed with tangent time constant and wave-speed theory in normal adolescents]

To understand the distribution of F-V curve configuration and the characteristics of tangent time constant (tau t), and to explore the mechanical mechanism for the formation of F-V curve configuration, we measured the tau t of high, mid, low lung volumes (tau t75, tau t50, tau t25) from F-V curves in 728 normal adolescents aged 8-19. The results showed that the distribution of the concave type was the highest among 4 types of F-V curve configuration with a range of 40%-70%. Its tau t features were tau t75 > tau t50 > tau t25 and magnitude of tau t75 > 1s. Then the concave type and its tau t features were called "adolescent fashion". Contrastedly, the distribution of the convex type was the lowest, only 4%-22%. The mechanical mechanism responsible for the formation of the concave type was analysed with the wave-speed theory. During the growth of adolescents, the lung elastic pressure and driving pressure increase with age. The diameters of airways increase, especially those of the peripheral airways with profuse branches. These changes lead to a decrease of resistance. Therefore, the critical flow (Vc) or wave-speed flow (Vmax) of peripheral airways is raised, and the flow there-in could hardly be limited. Thus the choke point (CP) will stay in trachea for a longer period, leading to the elongation of the plateau towards the tail or the concavity of the curve towards the volume axis and hence the formation of the concave type.