Introduction
Vibration response imaging (VRI) measures the vibration response energy generated from airflow to create a radiation-free, dynamic, real-time, structural and functional image of the respiration process. The characteristics of VRI in mechanically ventilated patients with chronic obstructive pulmonary disease (COPD) has not been previously studied.
Hypotheses
This was an observational study to compare the VRI of mechanically ventilated (MV) patients with no known pulmonary disease with those with COPD.
Methods
Five consecutive MV patients with COPD were compared with five consecutive MV patients with no known pulmonary disease. Using custom-designed software the vibration signals were fitted to a mathematical function and a gray level frame was constructed. At peak inspiration and expiration, spatial areas of the images were captured and the total area of the image calculated using ImageJ Software.
Results
In patients with normal lungs, the spatial distribution of the maximal signal expiratory vibration response image was lower than the maximal signal during inspiration. The mean decrease in area was 8103 pixels + 20,606 (P = 0.01) (Table 1). In patients with COPD the spatial distribution of the maximal signal expiratory vibration response image during expiration was higher than the maximal signal inspiratory image. The mean increase in area was 19,214 pixels + 6552 (P = 0.03) (Table 2).
Table 1.
Distribution of image area in patients with no pulmonary disease
| Patient 1 | Patient 2 | Patient 3 | Patient 4 | Patient 5 | |
|---|---|---|---|---|---|
| Inspiration | 93,735 | 55,618 | 55,573 | 86,432 | 79,791 |
| Expiration | 85,490 | 50,005 | 38,919 | 82,362 | 73,858 |
Table 2.
Distribution of image area in patients with COPD
| Patient 1 | Patient 2 | Patient 3 | Patient 4 | Patient 5 | |
|---|---|---|---|---|---|
| Inspiration | 25,831 | 60,0085 | 51,195 | 72,372 | 24,229 |
| Expiration | 64,484 | 63,139 | 71,231 | 73,628 | 57,300 |
Discussion
The increase in the image area during the expiratory phase in COPD patients may reflect increased airflow resistance causing increased vibration energy. Air trapping and auto-PEEP are other possible mechanisms accounting for the expiratory increase in image area.
Conclusion
VRI provides real-time non-invasive lung imaging of airflow in the mechanically ventilated patient. Mechanically ventilated COPD patients demonstrate a dramatically different VRI pattern than normal MV patients. VRI may provide important diagnostic information in COPD patients.