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Respiration pattern analysis

What Does This Channel Measure?

The calibrated respiratory pattern can be recorded using inductive plethysmography (e.g., Respitrace, LifeShirt) or pneumatic bellows (e.g., Lafayette). Most other techniques (e.g., strain gauge with piezoelectric pressure-voltage conversion using the Hall effect) are not linear and thus cannot be calibrated accurately. This channel measures the subject’s breathing activity, including respiration rate and lung volume. ANSLAB initially displays the raw data in five windows. For editing purposes, you are interested in figure 3, thoracic breathing, and figure 4, abdominal breathing.

You will notice that there is a basic cyclical pattern. Note: You must have done the respiration calibration analysis. ANSLAB will base lung volume related measures on an accurate calibration.

   
What Kind of Artifacts are Common in this Channel?

There are two common problems with respiration files.  The first is incorrect calibration.  Problems with calibration will not show up immediately, so be careful with this first step. The second type of common problem is irregularities due to technical error or movement artifacts.  Both irregularities deviate from the cyclical pattern and may include extreme spikes in lung volume.
 
How Are Artifacts Removed?

Note: Do not ‘over-edit’ respiration.  In general, if respiration is properly calibrated and observes a cyclical pattern, editing is not required for many experiments.  Baseline shifts will be filtered out.







If you see any huge irregularities in the data, that is, periods where you do not see a cyclic, regular breathing pattern, you want to edit these data. Most of the time, irregularities will be resets, manifested by sharp, vertical lines. If there are very extreme spikes in the signal due to technical difficulties, exclude those by selecting “edit thorax” or “edit abdomen”. In the window that opens you can exclude data by "exclusion boxes" (drag the mouse to define a ractangle spanned by an upper left to a lower left corner; when you release the mouse, all values between the left and right margins that are above the upper or below the lower margin will be excluded; interpolate by clicking on the right side of the window). After editing one window, quit it by clicking in the right bottom corner of that window. Then edit the other channel or, if you’re done, select "both channels o.k."
If there are no extreme spikes due to technical difficulties, but irregularities in the signal probably due to movement, you want to mark them as artifacts. To do that, select “both channels o.k.”  A window named figure 2 will pop open, displaying 9 computed parameters: RR: respiratory rate, V: minute ventilation, duty: inspiration time/total time, Pe: expiratory pause, Ti: inspiratory time, Vt: tidal volume, Flow: inspiratory flow rate, Te: expiratory time, Pi: inspiratory pause. The value displayed at the y-axis is the average.








Eyeballing those can give you hints as to where to expect artifacts. For example, the first red line showing inspiration time should be pretty constant, and spikes here are suspicious. You close that window by clicking in the right bottom corner, and you will then be asked “edit artifacts?” to which you answer “yes.” In the window that opens up now, ...








... showing thoracic and abdominal volume added up (lower part of figure 1), first look at the whole interval (press <i>). If you see suspicious periods, i.e. periods where the cyclic, regular pattern is interrupted, zoom in (<z> and two clicks to define the area). The activity signal (displayed in green in the upper window) and the thorax-abdomen desynchrony signal (in blue) can additionally help you recognize artifacts: If there’s a lot of activity or a lot of desynchrony, there might be artifacts in the respiration.  
You can then mark artifacts in the bottom graph by typing <b> plus mouseclick (beginning of artifact) and then <e> plus mouseclick (end of artifact). You can leave this window by clicking in the right bottom corner. Again, figure 2 will pop up. Close it by clicking in the right bottom corner, select "no" (do not edit artifacts) or "Save reduced data (existing files will be overwritten)" if you want to save your changes.


Individual onset/offset points of cycles can be edited by typing <'>, selection of which part of the cycle to reset in the following menu, and then clicking close to the point that you want to move, and a second time to the location where you want to move the point. This kind of editing is important if you are very interested in certain specialized parameters like expiratory pause time. The menu also allows to delete or add entire breathing cycles.

   
What Qualities Must Be Preserved In Editing?
     
If you use respiration data for transfer function spectral analysis of respiratory sinus arrhythmia it must be calibrated carefully. The most important quality to preserve is the cyclic breathing pattern so that respiratory rate can be estimated correctly.  Many irregularities in wave height and frequency can be ignored if they conform to a general cyclical pattern and if the averaging over a minute or so will overcome much of the misestimation error.
Be conservative when editing baseline shifts and movement artifacts.  Areas you exclude are interpolated as straight lines.  Therefore, exclude only clear artifactual spikes, but do not exclude small baseline shifts and slower ‘unusual’ phenomena.