First Evaluation of Ultrafast Ultrasound Coupled With Phrenic Stimulation for Noninvasive Diagnosis of Diaphragm Dysfunction.

BACKGROUND

Diaphragm dysfunction is an important and often unrecognized cause of dyspnea. The current gold standard, transdiaphragmatic twitch pressure (Pdi,tw), requires oesophageal and gastric balloon catheters and is infrequently used in routine care. We evaluated whether ultrafast ultrasound descriptors of costal diaphragm during bilateral phrenic magnetic stimulation can provide a noninvasive alternative for assessing diaphragm contractility.

METHODS

Thirty patients (19 men and 11 women) referred for suspected diaphragm dysfunction (median age 57 [42-63] years) underwent bilateral anterolateral magnetic stimulation with simultaneous ultrafast ultrasound and oesophageal/gastric pressure recordings. Peak diaphragm tissue velocity, acceleration and jerk were extracted. Associations with Pdi,tw were assessed using ridge regression. Diagnostic performance for detecting abnormal Pdi,tw (< 20 cmH2O) was evaluated using Bayesian receiver operating characteristic (ROC) analysis, including posterior mean AUC and 95% credible intervals. Agreement between predicted and measured Pdi,tw was assessed using Lin's concordance correlation coefficient and Passing-Bablok regression.

RESULTS

Twenty four of 30 patients (80%) had abnormal Pdi,tw. Ultrafast ultrasound descriptors correlated with Pdi,tw (Spearman's ρ: velocity 0.77 [95% CI, 0.57-0.89], acceleration 0.70 [95% CI, 0.41-0.87], jerk 0.67 [95% CI, 0.43-0.85]; all p < 0.0001). The multivariable ridge model explained 66% of the variance in Pdi,tw and showed high agreement with measured values (Lin's concordance correlation coefficient = 0.87 [95% CI, 0.75-0.93]). Bayesian ROC analysis demonstrated strong discrimination of diaphragm dysfunction (AUC = 0.91; 95% credible interval [CrI], 0.76-0.98). Using the clinical threshold of 20 cmH2O, model-predicted Pdi,tw yielded a sensitivity of 75% and specificity of 100%. The optimal velocity threshold for discriminating abnormal Pdi,tw was 10.25 mm·ms-1 (95% CrI, 6.12-18.58 mm·ms-1). The corresponding thresholds for acceleration and jerk were 408.6 mm·ms-2 (95% CrI, 122.6-952.4) and 3073 mm·ms-3 (95% CrI, 1038.8-11541.4), respectively.

CONCLUSIONS

Ultrafast ultrasound coupled with magnetic phrenic stimulation provides a feasible, noninvasive, nonvolitional assessment of diaphragm contractility. Diaphragm motion descriptors reliably predicted Pdi,tw and enabled accurate identification of diaphragm dysfunction. These findings support further clinical evaluation and warrant larger multicentre validation studies.