Instruction manual

5 Analysis 49
Also enter this X value in the text box below the graph. Clicking the Calibrate Difference
between Cursors button will calculate the required calibration value and place it in the
Spirometer Calibration window.
To account for offset in the spirometer, choose a time at the beginning of the record when
there is no flow through the spirometer and enter this value in the Use First N Seconds as Zero
text box. DataTrax2 will take the first N seconds, average them together and use the result to
set the zero-line of the Volume channel. This is necessary because the output of the air flow
sensor is always offset and any offset causes the Volume channel to display a volume change,
even though no air is flowing through the sensor.
The Volume integral can also be set to reset after a certain time or with every cycle. During
spirometry experiments, the volume trace drifts upward because the volume of exhaled air is
larger than the volume of inhaled air. Cooler inhaled air at room temperature occupies less
volume than warmer exhaled air. The Volume integral will drift up and out of view, as it reports
correct values, unless a periodic reset is employed.
Activating
Spirometry
Function
To apply the Spirometry function to a channel, click on the Add Function button in the
Channel bar. Select Spirometry from the Function menu.
Channel
Math
The Channel Math function applies a user-defined function to points from up to four data
channels and displays the output in a computed channel. There are four Variables A, B, C and
D, each of which can be associated with a user selectable data channel. For example, if you
wanted to divide Channel 1 by Channel 2. Click on the Add Function button on either the
Channel 1 or Channel 2 channel bar. Select the Channel Math option. Select A to be Channel 1,
and B to be Channel 2. Set the channel value to be A/B.
Figure 5-4: The Channel Math dialog window. eg, output channel is equal to (RawCh 1 plus Raw Ch 2 / 2) * Comp Ch 1 in grams
The result is every Channel 1 data point divided by the corresponding Channel 2 data point. A
full range of trig and log functions, as well as the common mathematical operators, are
available in the Channel Math dialog window. The Unit Name for the calculated value can be
specified in a box. There is also a Check Expression feature, which will check for errors like