Abstract
Inspiratory muscle conditioning at a lower lung volume based on the principles of muscle thixotropy decreases end-expiratory chest wall volume (Vcw) during resting breathing. The aim of the present study was to determine the deflating effect of thixotropy conditioning of inspiratory muscles on dynamic increases in operating chest wall volumes (end-expiratory Vcw and end-inspiratory Vcw). We examined the deflating effect on hyperinflation induced by continuous positive airway pressure (CPAP; 10 cm H 2 O) in 13 healthy men with respiratory inductive plethysmography. Conditioning at maximal expiratory volume, positioned 1.30 ± 0.57 L below true functional residual capacity (FRC), decreased end-expiratory Vcw by 0.16 ± 0.12 L and end-inspiratory Vcw by 0.20 ± 0.14 L at 180 s (P < 0.01). Inspiratory capacity (1.59 ± 0.45 L) and inspiratory reserve volume (1.18 ± 0.40 L) were greater than baseline values during CPAP breathing (1.44 ± 0.49 L and 0.99 ± 0.41 L, respectively; P < 0.01). Although small changes in these parameters were observed immediately after conditioning at or above true FRC, these changes disappeared by 180 s after conditioning. Thus, conditioning should occur at an expiratory position below true FRC to result in lasting decreases in operating chest wall volumes during CPAP-induced hyperinflation. [J Physiol Sci. 2007;57 Suppl:S213]
