Tangent time constant and wave-speed mechanism of F-V curve configuration in smokers and clinical significance
Huang, G.; Wang, J.; Huang, J.
Hua Xi Yi Ke da Xue Xue Bao 31(1): 68-71
2000
ISSN/ISBN: 0257-7712 PMID: 12501617 Document Number: 521665
This study was conducted to explore the mechanical mechanism of the formation of F-V curve configuration with tangent time constant (tau 1) and wave-speed theory for smokers. F-V curves were measured on 22 passive smokers and 94 active ones. FVC, V75, V50 and V25 were obtained, and tangent time constants at high, mid, low lung volumes, tau t75, tau t50 and tau t25 were calculated, and analysed with wave-speed theory. The results showed that the chief changes taking place only in heavy smokers and convex type of F-V curve were: decreased V50 and V25; tau t25 > or = 1s; tau t75-tau t50 < tau t25 in "trumpet fashion" change; and tau t75 < tau t50 < tau t25 in "tower fashion" change. Then, tau t25 > or = 1s, tau t75-tau t50 < tau t25 and tau t75 < tau t50 < tau t25 were assigned as three tau t characters of smoking effect. They led to an increased convexity of the convex type of F-V curve, and reflected the decrease of small airway functions. Similar to the decrease of V50 and V25, they have important significance in assessing small airway functions and thus merit clinical use.