Comparison of Diaphragm Thickness Measurements Among Postures Via Ultrasound Imaging

Abstract

BackgroundAssessment of diaphragm contraction may be useful for identifying impairments in patients with movement dysfunction involving trunk stabilization, respiration, or both. Real-time ultrasound imaging is a readily available technology that can be used to quickly assess this aspect of diaphragm activity. Although previous studies have examined diaphragm contraction in the supine posture, a comparison of measurements between supine and upright postures has not been made. ObjectiveTo examine whether diaphragm thickness measurements differ among 3 different body postures in healthy subjects. DesignDescriptive repeated measures. SettingClinical laboratory. Patients (or Participants)Twenty-four healthy subjects (12 male and 12 female) aged 22-35 years old were recruited and completed the study. MethodDiaphragm thickness was assessed in via B-mode ultrasound imaging in supine, seated, and standing postures. Measurements of diaphragm thickness were taken in the zone of apposition during maximal inspiration to total lung capacity (TLC) and end-tidal expiratory lung volume (EELV). A thickness ratio (inspiration thickness/expiration thickness) was calculated to compare relative diaphragm contraction during each condition. Main Outcome MeasurementsThe primary dependent variable was diaphragm thickness (mm). ResultsAverage diaphragm thickness at EELV and maximum TLC were more than 20% greater in the seated and standing postures than in supine (P < .05). Moreover, the diaphragm was approximately 205% thicker at TLC than at EELV (P < .05). Relative inspiratory to expiratory thickness ratios (TLC/EELV) did not differ among postures (P = .24). ConclusionsThe diaphragm is thicker when the body is in more upright postures (standing and sitting versus supine) perhaps due to greater vertical gravitational load on the muscle and associated change in the resting length of the muscle fibers. Thus it appears that ultrasound imaging may be a sensitive tool to examine changes in diaphragm contraction during varying postural tasks. Level of EvidenceIV