A novel application for assessing diaphragmatic function by ultrasonic deformation analysis in noninvasively ventilated healthy young adults

Purpose: Noninvasive pressure support ventilation is intended to relieve the load on respiratory muscles and to prevent exhaustion. This includes continuous positive airway pressure (CPAP) as well as pressure support ventilation (PSV). Speckle tracking echocardiography (STE) allows quantification of tissue deformation by tracing characteristic grayscale patterns, independent of the acquisition angle. The aim of the present study was to assess the applicability of using STE as a way to investigate diaphragm movement using deformation analysis as a parameter for respiratory workload.

Materials and methods: Healthy male subjects (n = 13, 27 ± 7 years) were treated while in a seated supine position with the following respirator settings: regular breathing, 5 mbar CPAP, CPAP + 5 / + 10 / + 15 mbar PSV. A 2 - 4 MhZ M5S phased array sector transducer was used on a Vivid E 9 (GE, Horton, Norway) to visualize the diaphragm. The inspiratory peak transverse strain was measured as a parameter of maximal inspiratory muscle workload and compared to the M-mode-based fractional thickening (FT).

Results: Both the FT and the transverse strain increased significantly under CPAP and PSV. The transverse strain correlated well with the FT (r = 0.753; p < 0.001).

Conclusion: The results measured by STE were comparable to the M-mode-based measurements. The capturing of a larger diaphragmatic sample area and movement tracking possibly lead to higher precision compared to one-dimensional M-mode. The use of STE in patients might provide a reproducible, bedside method to analyze the respiratory workload. Due to the larger sampling area, it might prove superior to mere M-mode acquisition.