Evaluation of Lateral Abdominal Muscle Activity during Expiratory Threshold Loading by Ultrasonography

Abstract

We have examined whether the lateral abdominal muscle activity during expiratory loading can be noninvasively evaluated using ultrasonography. This study included 12 healthy adult men, and measured the thicknesses of their lateral abdominal muscles at the end of inspiration and the end of expiration, and the thickness differences when 5%, 10%, and 15% of the maximal expiratory pressure were loaded as expiratory threshold loads. Tidal volume, inspiratory reserve volume and expiratory reserve volume were also measured at the same time. Obtained data were compared by expiratory threshold load, and correlation between muscle thickness and the thickness difference was assessed. Muscle thickness at the end of expiration and thickness difference significantly increased in proportion to the expiratory threshold load, and were accompanied by increase of tidal volume. Additionally, a significant positive correlation was found between muscle thickness and the thickness difference. The results of this study indicate that expiration activities of the lateral abdominal muscles can be evaluated by ultrasonography, and that the thickness difference reflects expiration activities.