PURPOSE: Vibration response imaging (VRI) is a novel technology that utilizes sophisticated software and surface skin sensors to record, analyze and display vibrations as a non-invasive measure of lung ventilation. The purpose of this study is to compare the spatial distribution of lung vibration, a likely surrogate of airflow, in the same patients on assist volume control ventilation (AVC) and low-level pressure support ventilation (PSV).
METHODS: We performed serial VRI during maintenance AVC and immediately following initiation of spontaneous breathing trial using low-level PSV in 41 mechanically ventilated patients. Based on predetermined criteria, respiratory cycles free of artifact were chosen for analysis and the maximal inspiration image was used for analysis. Areas of images were calculated digitally using the program ImageJ. The areas of right and left lung measured at maximum vibration energy during inspiration were compared, maintenance AVC versus low-level PSV. Statistical analysis was performed using t-test and the t-distribution.
RESULTS: Tidal volume was 530 ml ± 90 for AVC and decreased to 422 ml ± 172 for PSV (p=0.0002). The mean areas of both lungs were 66.05 ± 9.98 and 68.0 ± 10.51 (mean in kilopixels ± stdev) in AVC and PSV images, respectively (p=0.03). There was a mean increase of 3.27 % ± 9.83 in the areas of the lungs during PSV compared to AVC (p=0.02).
CONCLUSION: Despite lower tidal volume, PSV (compared to ACV) produced a greater spatial area of lung vibration. The increase in distribution of vibration during PSV could represent increase in patient generated negative intrapleural pressure during inspiration, and synchronization with positive pressure from the ventilator. This confirms the observations from an earlier smaller study by our group (Jean S, et. al, Crit Care Med 2005; 33(12): A140).
CLINICAL IMPLICATIONS: Using vibration as a surrogate for airflow, VRI allows comparison of distribution of vibration between different modes of ventilation which may help to determine the best mode and, during a weaning trial, may help predict which patients can be extubated successfully.
DISCLOSURE: Smith Jean, University grant monies NA; Grant monies (from sources other than industry) NA; Grant monies (from industry related sources) Deepbreeze Ltd.; Shareholder NA; Employee NA; Fiduciary position (of any organization, association, society, etc, other than ACCP NA; Consultant fee, speaker bureau, advisory committee, etc. Joseph Parrillo, MD, FCCP; R P Dellinger, MD, FCCP; Other NA; Product/procedure/technique that is considered research and is NOT yet approved for any purpose, Vibration response imaging.