The purpose of the study was performed to investigate reliability of the measurements of expiratory muscles during respiratory conditions of resting and forced expiratory using ultrasonography. Additionally,
this study to determine the correlation between peak expiratory flow(PEF) and expiratory muscle thickness.
Forty-five normal subjects in their 20s participated with no special disease according to a pre-survey and
questionnaire, and received “Informed consent” which state the voluntary participation of study. The
expiratory muscle thicknesses under respiratory conditions of resting and forced expiration in the rectus
abdominis, internal oblique, external oblique, and transverse abdominis muscles were measured by B-mode
ultrasonography at the end of a expiration in the supine position. The peak expiratory flow was obtained
using a spirometer that performed in the sitting position to measure total lung capacity. The rectus
abdominis, internal oblique, external oblique muscles under respiratory conditions of resting and forced
expiration showed a high level of reliability of the thickness measurement, but that of transverse abdominis
muscle was relatively low. The mean values of peak expiratory flow was 512.64±76.40ℓ/min. There was
no significant correlation between peak expiratory flow and the thickness of rectus abdominis, internal
oblique and transverse abdominis muscles. There was a significant positive correlation between peak
expiratory flow and the thickness of external oblique muscle, Correlation coefficient was 0.303. The
thickness of the expiratory muscles is influenced by voluntary respiration, and assessment of the thickness
by means of ultrasonography is adequately reliable. Therefore, Physiotherapists applying selective
strengthening exercise of external oblique muscle may be considered intervention method to improve peak
expiratory flow that patients with respiratory disease to facilitate airways clearance.