New Technology Converts Lung Vibrations Into Real-Time Images

Key Point

Vibration response imaging, a novel bedside technology, provides real-time images of respiratory function, noninvasively and without the use of radiation.

ORLANDO—A novel bedside imaging technology may be useful in evaluating mechanically ventilated patients, investigators from Cooper University Hospital in Camden, New Jersey, reported at the 36th Critical Care Congress of the Society of Critical Care Medicine (SCCM). The technology—vibration response imaging (VRI)—uses software to record and analyze lung vibrations during breathing and to display the vibrations as real-time structural and functional images. VRI is noninvasive and radiation-free, stated researcher Smith Jean, PhD, of the Division of Critical Care Medicine at Cooper University Hospital.

Dr. Jean headed a small study involving two groups of eight mechanically ventilated patients. Patients in the first group (the study group) had focal chest radiograph abnormalities, while the second group (controls) had normal chest radiographs. In both groups, VRI was performed on the same day that chest radiography was used to record maximal inspiration vibration over 20 seconds.

“In the study group, lung vibration energy was consistently lower in the affected lung than in the uninvolved lung,” Dr. Jean related. “On average, the difference between the percent of total vibration energy in the affected lung minus the percent vibration energy in the nonaffected lung was 24.16%. For the control group, the difference was 9.17%.” VRI may be useful to predict the likelihood of an asymmetric lung parenchymal process, concluded Dr. Jean.

One of his associates, Ismail Cinel, MD, PhD, was the lead investigator in a separate VRI study of 34 hemodynamically stable patients being weaned from mechanical ven­tilation. Dr. Cinel and colleagues had hypothesized that lower-lung vibration as a surrogate for airflow would be greater when patients were switched from assist volume control to low-level pressure support during spontaneous breathing trials.

That hypothesis proved to be correct. Compared with volume control mode, a pressure support level of 5 cm H2O was associated with a significant increase in VRI geographic area, despite a lower tidal volume. “The pressure support mode causes a shift of vibration intensity towards the lower lung regions,” said Dr. Cinel, who is also in the Division of Critical Care Medicine at Cooper University Hospital. “Better synchronization with the ventilator and greater downward movement of the diaphragm may be the physiologic explanation for the redistribution of vibration energy. Furthermore, when patients were used as their own controls, there was a significantly increased percentage of vibration energy distribution to the middle and lower lungs,” pointed out Dr. Cinel.

The study confirmed findings previously reported by his group in a similar investigation. “VRI offers a physiologic principle for why pressure support might produce more physiologic ventilation than alternative modes,” Dr. Cinel suggested.

Earlier this year, the Cooper University Hospital investigators published a study comparing VRI findings in 38 mechanically ventilated patients who received three modes of ventilatory support: assist volume control, assist pressure control, and pressure support. The purpose of this study was to evaluate differences in regional lung vibration at maximal inspiration during each mode with constant tidal volumes. SCCM presenter R. Phillip Dellinger, MD, Director of the Division of Critical Care Medicine at Cooper University Hospital, was the lead investigator.

The percent increases were 28.5% when patients’ mode of support was changed from volume control to pressure support and 18.8% when changed from volume control to pressure control. There was a concomitant decrease in the area of the image in the middle lung regions of 3.6% and 3.7%, respectively. “In addition, analysis of regional vibration intensity showed a 35.5% relative percent increase in the lower region with pressure support versus volume control,” the investigators said. “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,” they suggested.           

—Timothy Begany

Reference
Dellinger RP, Jean S, Cinel I, et al. Regional distribution of acoustic-based lung vibration as a function of mechanical ventilation mode. Crit Care. 2007;11:R26.
Jean S, Dellinger RP, Steele EA, et al. Increased spatial distribution of airflow in lungs with low-level pressure support ventilation compared to maintenance ventilation. Crit Care Med. 2005;33:A114.

Return to table of contents