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Effect of the inspiratory flow pattern on inspiration/expiration transition of lung vibrations in mechanically ventilated patients
Critical Care volume 12, Article number: P304 (2008)
Mechanical ventilation can be performed using different inspiratory flow patterns. We used vibration response imaging (VRI) technology to ascertain the intensity of lung vibration with different inspiratory flow patterns during various modes of mechanical ventilation.
VRI was performed in succession during volume control ventilation with a square and decelerating inspiratory flow waveform, a pressure control waveform and a pressure support waveform. The total lung vibration energy transmitted to the posterior thorax (from 36 sensors) was plotted over time and the transition of vibrations from inspiration to expiration noted.
During volume control ventilation with a square inspiratory flow waveform, peak inspiratory flow (PIF) is immediately followed by peak expiratory flow (PEF) and, as such, the separation of peak inspiratory (I) and expiratory (E) lung vibrations as transmitted to the chest wall surface was minimal or absent consistently (Figure 1a). During pressure support ventilation, PIF and PEF are separated – resulting in a consistent separation of I and E peak lung vibration (Figure 1b). During pressure control ventilation with sufficient I time to allow inspiratory flow to return to a baseline as near-baseline level, the valley was consistently widened between the peak I and E lung vibration energy, reflecting the decrease in vibration energy associated with lower end-inspiratory airflow (Figure 1c).
When the flow-time waveform recorded between the patient and the ventilator is compared with the vibration waveform summed from surface sensors, two patterns emerge: as the time between PIF and PEF increases, the separation of peak I and E lung vibration energy increases; and as end-inspiratory flow decreases, the valley between peak I and E vibration deepens. The decelerating flows that gradually diminish to zero will therefore produce the greatest separation in respiratory vibrations. There could be clinical relevance as to the effect of the inspiratory flow waveform on vibration transition in the chest.
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Jean, S., Cinel, I. & Dellinger, R. Effect of the inspiratory flow pattern on inspiration/expiration transition of lung vibrations in mechanically ventilated patients. Crit Care 12, P304 (2008). https://doi.org/10.1186/cc6525
- Pressure Support
- Peak Expiratory Flow
- Pressure Support Ventilation
- Inspiratory Flow
- Vibration Energy