抄録
Thixotropy is a passive property of the skeletal muscle that depends on the muscle's immediate history of contraction and length change. We showed that inspiratory muscle thixotropy affects the end-expiratory position of the rib cage. The present study aimed to test whether changes in end-expiratory chest wall volume (Vcw) occurs after thixotropic inspiratory muscle conditioning in normal subjects (n = 32). We first examined effects of the conditioning on end-expiratory Vcw of succeeding five breath cycles with respiratory induction plethysmography. Subjects participated in the conditioning at three different Vcw (60% inspiratory capacity [IC] + end-expiratory Vcw of baseline breathing [EEB], EEB, and residual volume [RV]) giving one of two levels of inspiratory effort (no effort or maximal inspiratory effort) with airway closure in the sitting position. End-expiratory Vcw increased after conditioning at 60% IC + EEB and decreased after conditioning at RV. We then measured the time course of changes in spirometrically determined IC, which confirmed thixotropic changes in end-expiratory Vcw. A decrease in the IC was found at 60 s after conditioning performed at the higher volume. However, the decrease disappeared until 180 s. Conditioning at the lower volume was followed by an increase in the IC, which was maintained even after 180 s. Furthermore, the thixotropic inflation/deflation of the chest wall was proved by the helium-dilution FRC and esophageal pressure measurements. In conclusion, thixotropy conditioning of inspiratory muscles changes end-expiratory Vcw. [J Physiol Sci. 2006;56 Suppl:S75]
