Comparison of shear-wave elastography to state-of-the-art respiratory function testing to measure the range of forces generated by the diaphragm muscle

The diaphragm muscle is important in both sustaining ventilation and performing higher-force behaviors necessary for maintaining airway patency. Ventilatory behaviors (i.e., eupnea and response to hypoxia-hypercapnia) require only ~20% of maximal force generation, whereas coughing requires forces ~60% of maximal. Existing techniques to measure the full range of forces generated by respiratory muscles are limited by their invasiveness (e.g., balloon manometry for transdiaphragmatic pressure (Pdi) measurements), requirements for training, supervision and subjectivity (e.g., maximal inspiratory and expiratory pressures). Ultrasound-based shear-wave elastography (SWE) assesses muscle stiffness and has shown promising results in being used as a surrogate for Pdi to evaluate diaphragm muscle force. Previous literature has demonstrated a correlation between diaphragm SWE and Pdi at lower force behaviors and the goal of the present study was to evaluate the efficacy of SWE-based measurements of the diaphragm in correlating with Pdi measurements across the range of forces generated by the diaphragm. In this pilot study, we recruited 6 male and 5 female healthy volunteers. Subjects were positioned in a seated position with their torso unsupported. Pdi was measured during graded inspiratory threshold loading trials using a POWERbreathe Plus commercial inspiratory loading device, as well as during maximal inspiratory pressure (MIP). Simultaneously, SWE was performed at the zone of apposition in the right anterior axillary line, and diaphragm Young’s modulus and shear wave speed were subsequently measured. The average Pdi during MIP testing was 149 ± 66 cm H 2 O. Pdi during inspiratory loading at a low resistance was 39 ± 14 cm H 2 O and at a high resistance was 78 ± 29 cm H 2 O. Subjects were able to generate an average Pdi range of 39 ± 19 cm H 2 O across the graded resistance levels, and the average percent of MIP obtained was 54 ± 13%. Average Young’s modulus as measured with SWE during inspiratory loading at a low resistance was 46 ± 19 kPa and at a high resistance was 104 ± 19 kPa. From low to high resistance, Pdi, Young’s modulus, and shear wave speed increased by an average of 100%, 126%, and 59%, respectively. Taken together, SWE is a promising method of non-invasive assessment of diaphragm muscle forces across a range of voluntary behaviors. Support from NIH grant R21 DA055848 and the Mayo Clinic. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.