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 rectangle 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 later on. Next, 10 computed parameters are displayed:
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 and IbrI: interbreath interval. 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 green line showing inspiration time should be
pretty constant, and spikes here are suspicious. To edit artifacts, you
can either change inidiviual cycle onsets, offsets and maxima/minima
manually in the 'Raw'-data-mode, or do a rather rough outlier exclusion
in the 'Event'-data-mode (see 'the NAVIGATION section' for details
about the Raw/Event-Modes). When zooming in sufficiently in
'Raw'-data-mode, respiration onset/offset/maximima/minima-markers are
displayed as shown in the graph below:
The activity
signal (displayed in green in the bottom 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 take out entire
breathing cycles using the 'delete
cycle'-button, insert an entire cycle using the 'insert cycle'-button, or
move onset/offset/minima/maxima-markers using the 'insert insp. end'-, the 'insert exp. end'-, the 'insert insp. onset'- and
the 'insert exp. onset'-buttons.
Individual onset/offset points of cycles are edited by 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.
You can mark artifacts by using the 'define artifact'-button.
After pushing this button, click twice on the data window to mark
beginning and end of the artifact. A horizontal red bar is then
displayed to symbolize the artifact definition. When variables are
saved, artifact intervals will be filled with 'NaN's.
Once you have finished editing, push 'Resume' and choose 'Save reduced
data'
if you want to save your changes.
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.