This technical note describes the technique to validate the volume calculation using signal data and calculated parameter data from selected regions of valid breaths.
A finite impulse response (FIR) filter is applied to the waveform signal displayed on the graph only. The data in the table are calculated from the unfiltered waveform signal. The purpose of the filter is to display a “clean” waveform. The filter can cause the frequency content of the waveform to be attenuated and display a delayed response.
A good breath has the following characteristics:
- Does not have rapid change in rate and/or offset (Figure 4).
- Has similar breaths preceding and following it (Figure 3).
- FinePointe marks the breath as valid (the waveform color changes to white).
- A “reset” did not occur during the breath. A reset is characterized by a sharp vertical line on the waveform going to the zero line (Figure 5).
- The box flow signal does not have a lot of noise artifact on it (Figure 6).
Method to validate
- Load a WBP volume study in FinePointe that has good breaths (see Good Breaths section).
- Ensure that the Data Logging Mode is set to Breath Based and the log interval and breath in average are both set to 1.
Figure 1 Recording is set to display and report 1 breath.
- The box flow and volume signals need to be displayed.
- Locate a region of clean data with the following characteristics:
- At a minimum 2 consecutive good breaths prior to and 1 good breath following the good breath to be measured (see Good Breaths sections for characteristics).
- The temperature data during the good breath to be used should be stable and not changing in value in the middle of the breath waveform.
- Highlight (left click and drag) the 3rd good breath to include the area around the volume peak (Figure 2).
- Right click in the highlighted region and select “Find in Table”
- Record the peak volume (max) measurement which is located above the volume waveform (Figure 2).
- Multiply by the compensation value displayed on the table by the peak volume recorded in step 7.
- Compare the value calculated in the previous step (step 8) to the value displayed as TVb in the table. This value should be within +/- 10%*.
- This corrected value can be different from manual calculation due to the filtering that is applied to the waveform signal (see FIR Filtering Section)
Figure 2: The above screenshot shows a respiratory cycle that meets the criteria as a good breath. The area around the peak volume has been highlighted. The peak volume value, 0.0114, is displayed in a textbox above and to the right of the peak value. This value should be multiplied by the comp value of 12 and compared to the tidal volume of 0.1446.
Figure 3: The top waveform shown is the Box Flow signal with the volume signal shown below it.
Figure 4: The example shown above shows a quick change in respiratory that is short in duration. This is an example of an area that should not be used to verify the tidal volume of the waveform with the volume value shown in the table.
Figure 5: The end of the volume waveform has a substantial decline due to the "reset" to bring the waveform back to the zero line.
Figure 6: The box flow signal (top) has a lot of noise artifact on the signal as evident by the spikes on the waveform.