What Does This Channel
Measure?
Typically the arterial pressure signal was measured using the Finapres,
Portapres
or Finometer device. The measures extracted by ANSLAB from the arterial
pressure waveform are systolic, diastolic and true mean arterial blood
pressure. In addition, pulse pressure and pulse transit time are
calculated (from the ECG R-wave to the steepest upstroke in the
arterial pressure signal). The algorithms and displays are almost the
same as for analysis of pulse plethysmography signals.
What Kind of Artifacts are Common in this Channel?
Artifacts in Finapres look very much like artifacts in finger or ear
plethysmography. Unusual spikes that distort the mean are
considered outliers.
Automatic pressure calibration reset stairs appear as flat looking
periods in the raw signals. Those are only to be worried about if they
occur more often than once per minute, and are mostly a problem if
spectral
analysis of the systolic pressure is planned (e.g., for analysis of
cardiac baroreflex control).
How Are Artifacts Removed?
See explanations for the pulse plethysmography analysis for details. In
short, outliers are removed by first selecting
the variable to be edited with a mouse click, and then defining a box
for outlier exclusion with the mouse. When done editing one
variable, it often makes sense to synchronize the other channels'
missing data points, since artifacts will typically affect each derived
parameter. Clicking above the signals in the left quadrant of the upper
screen synchronizes missing values of all channels, clicking in the
rightmost quadrant restores the original
signals. If you are uncertain if
something is an artifact or not, click in the left bottom corner,
choose option [10], click twice in the signal to define the area you
want to look at, and then go to figure No. 3, which will display the
raw signal for the selected area. This window can be simply closed by
clicking on the cross in the right upper corner.
After editing, you can leave the windows by clicking in the right
bottom corner. Then choose "Save reduced data" if you want to save your
changes.
What Qualities Must Be
Preserved In Editing?
Systolic blood pressure will be used for spectral analysis for
estimation of baroreflex
sensitivity and therefore has to be analyzed carefully, since single
spikes can distort the quality of the spectral analysis easily. That
means: If in doubt, take spikes, i.e. outliers, out, even if the mean
is
not altered a lot. The other parameters can be edited less
carefully, since only the means over periods are usually considered.