Instruction manual

5 Analysis 47
Negative: Only the negative data points are included in the calculation.
Data points with values above zero make the Integral larger, those with values less than zero
make the Integral smaller. To successfully complete the calculation of the Integral, the location
of the zero-line needs to be known.
Setting the baseline of the raw data channel to zero is the more important of the two require-
ments since this function defines the difference between positive and negative areas of the
recording. If the baseline of the raw data record is in the positive range of amplitudes, then the
Integral will have a positive slope, even though no signal is present. Conversely, if the baseline
of the raw data is in the negative range, the Integral will have a negative slope.
Zero As mentioned above, the Integral function adds the amplitudes of successive data points and
plots the total. The problem is determining where the zero-line is located. DataTrax2 and most
other data programs take the value zero volts as the zero-line. If real units, such as grams or
mmHg are used, the DataTrax2 software will take the zero units value as zero.
DataTrax2 also has a Use First “Number” seconds as zero option. The data values for the
first “Number” of seconds collected are averaged and used by the program as zero. This
feature is particularly useful when trying to integrate signals that are difficult to zero manually.
An example of the application of this feature is illustrated in Figure 5-2 on page 47. The output
of a respiratory flow sensor is the raw data displayed on the upper channel in each window; the
lower channel in each window is the integral of the upper channel, or the volume flowing through
the sensor.
In this example, the setting of zero is critical because any offset of the raw data from zero will
be taken as a flow and, subsequently, be interpreted as a volume. Two examples of the respi-
ratory integral are shown. In each case the flow sensor has a small, but stable offset. In the first
example, the integral shows constant increase in volume, even as the flow is constant. In the
second record, where the Use First “Number” seconds as zero option is used, the initial flow
is constant and is set to zero, so the initial volume is zero. When the flow increases to a level
above the “effective” zero-line, then the volume will increase on the integral channel.
Figure 5-2: Integral without Zero.