Appropriate body position and site for diaphragm ultrasound: Comparison with inspiratory mouth pressure

Objective

This study aimed to examine the appropriate body position and anatomical site for DUS through comparisons with maximal inspiratory pressure (MIP).

Methods

Thirty healthy adults were included in the study. MIP was measured using a spirometer. DUS was performed in both the right and left intercostal spaces in both sitting and supine positions. The diaphragm thickness at functional residual volume (TD_FRC) and total lung capacity (TD_TLC) were measured, and the fractional change in diaphragm thickness (TF) was calculated under each condition. To assess interobserver reproducibility, DUS was performed by an experienced examiner and a novice examiner.

Results

Among the DUS parameters, the TD_FRC measured at the right intercostal space in the sitting position showed the strongest correlation with MIP (r = 0.68, p < 0.001). The correlations of TD_TLC with MIP tended to be inferior to those of TD_FRC with MIP, and the TF parameters did not correlate significantly with MIP. DUS measurements in the supine position demonstrated greater reproducibility than those in the sitting position, and those at the right intercostal space tended to be better than those at the left intercostal space.

Conclusion

When evaluating respiratory muscle function during inspiration using DUS, TD_FRC at the right zone of the apposition in the sitting position was found to be appropriate. DUS measurements at the right zone of apposition in the supine position were considered adequate for clinical use because the influence of examiner experience was small.