title: Regional distribution of acoustic-based lung vibration as a function of mechanical ventilation mode.
abstract: BACKGROUND
  There are several ventilator modes that are used for maintenance mechanical ventilation but no conclusive evidence that one mode of ventilation is better than another. Vibration response imaging is a novel bedside imaging technique that displays vibration energy of lung sounds generated during the respiratory cycle as a real-time structural and functional image of the respiration process. In this study, we objectively evaluated the differences in regional lung vibration during different modes of mechanical ventilation by means of this new technology.
  
  
  METHODS
  Vibration response imaging was performed on 38 patients on assist volume control, assist pressure control, and pressure support modes of mechanical ventilation with constant tidal volumes. Images and vibration intensities of three lung regions at maximal inspiration were analyzed.
  
  
  RESULTS
  There was a significant increase in overall geographical area (p < 0.001) and vibration intensity (p < 0.02) in pressure control and pressure support (greatest in pressure support), compared to volume control, when each patient served as his or her own control while targeting the same tidal volume in each mode. This increase in geographical area and vibration intensity occurred primarily in the lower lung regions. The relative percentage increases were 28.5% from volume control to pressure support and 18.8% from volume control to pressure control (p < 0.05). Concomitantly, the areas of the image in the middle lung regions decreased by 3.6% from volume control to pressure support and by 3.7% from volume control to pressure control (p < 0.05). In addition, analysis of regional vibration intensity showed a 35.5% relative percentage increase in the lower region with pressure support versus volume control (p < 0.05).
  
  
  CONCLUSIONS
  Pressure support and (to a lesser extent) pressure control modes cause a shift of vibration toward lower lung regions compared to volume control when tidal volumes are held constant. Better patient synchronization with the ventilator, greater downward movement of the diaphragm, and decelerating flow waveform are potential physiologic explanations for the redistribution of vibration energy to lower lung regions in pressure-targeted modes of mechanical ventilation.
authors.affiliation: Division of Cardiovascular Disease and Critical Care Medicine, Robert Wood Johnson School of Medicine, University of Medicine and Dentistry of New Jersey, Cooper University Hospital, Camden, NJ 08103, USA. dellinger-phil@cooperhealth.edu
authors.forename: R Phillip
authors.initials: RP
authors.lastname: Dellinger
authors.forename: Smith
authors.initials: S
authors.lastname: Jean
authors.forename: Ismail
authors.initials: I
authors.lastname: Cinel
authors.forename: Christina
authors.initials: C
authors.lastname: Tay
authors.forename: Susmita
authors.initials: S
authors.lastname: Rajanala
authors.forename: Yael A
authors.initials: YA
authors.lastname: Glickman
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Parrillo
mesh_terms: D000162:Acoustics; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008168:Lung / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D011312:Pressure; D012123:Pulmonary Ventilation; D012121:Respiration, Artificial / Q000379:methods*; D013223:Statistics as Topic; D013990:Tidal Volume; D014732:Vibration