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.