Ultrasound assessment of respiratory muscle movement to predict inspiratory effort

Guo Xinqiao; Wang Jinrong

doi:10.3969/j.issn.1002-1949.2025.08.007

Abstract：Objective To assess respiratory muscle function by using ultrasound in healthy adults under varying inspiratory efforts and to establish a physiological model for predicting inspiratory effort.Methods A cross-sectional study was conducted in healthy subjects who met the inclusion criteria from June 2022 to December 2022.Inspiratory capacity during quiet breathing,moderate inspiration,and maximal inspiration were measured by using a portable pulmonary function meter to evaluate inspiratory effort.Simultaneously,bedside ultrasound was used to assess right diaphragm excursion,diaphragm thickness,and intercostal muscle thickness in these three states.The thickening fractions of the right diaphragm and intercostal muscle were calculated.Correlations of diaphragm excursion,diaphragm thickening fraction,intercostal muscle thickening fraction with inspiratory capacity were analyzed.Receiver operating characteristic curves were plotted to determine optimal cut-off values for diaphragm excursion,diaphragm thickening fraction and intercostal muscle thickening fraction based on area under the curve(AUC).Results A total of 65 subjects completed screening with an average age of(27.03±4.73)years;24 participants were male(37％).Diaphragm excursion during moderate and maximal inspiration was higher in males than in females(all P＜0.05).There were no statistically significant differences in diaphragm excursion during quiet breathing,diaphragm thicking fraction and intercostal muscle thickening fraction under different respiratory states between males and females(all P＞0.05).Diaphragm excursion as well as its associated thickening fractions showed significant correlations with inspiratory capacity(mL/kg ideal body weight),with correlation coefficients r being 0.83 for diaphragm excursion,0.75 for diaphragm thickening fraction,and 0.69 for intercostal muscle thickening fraction respectively(all P＜0.05).The linear regression equations were diaphragm excursion(cm)=1.26+0.09 × inspiratory capacity(mL/kg ideal body weight),diaphragm thickening fraction=-0.23+0.06 × inspiratory capacity(mL/kg ideal body weight)and intercostal muscle thickening fraction=-0.025+0.005 × inspiratory capacity(mL/kg ideal body weight).If≥moderate inspiratory effort was defined as relative inspiratory effort,the AUC of diaphragm excursion for predicting inspiratory effort was 0.96,the Youden index was 0.82,the best cut-off value was 2.33 cm,the sensitivity was 87.69％,and the specificity was 93.85％.The AUC of diaphragm thickening fraction for predicting inspiratory effort was 0.97,when the Youden index was 0.82,the best cut-off value was 0.45,the sensitivity was 89.23％,and the specificity was 92.31％.If the intercostal muscle thickening fraction＞0 was defined as absolute inspiratory effort,the AUC of inspiratory capacity for predicting inspiratory effort was 0.95,and when the Youden index was 0.80,the best cut-off value was 16 mL/kg ideal body weight,the sensitivity was 93.16％,the specificity was 87.18％,the corresponding diaphragm excursion was 2.70 cm,and the diaphragm thickening fraction was 0.73.Conclusions The use of ultrasound to assess the respiratory muscle motor function can determine the inspiratory effort in real time.