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Factors That May Affect Results
7
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012-08856B
Factors That May Affect Results
In your graphs of Total Flow and Lung Volume, you may notice a slow drift or slight
fluctuation in the baseline. These can be eliminated, in most cases, as described
below. Note that slow baseline changes usually do not significantly affect the
measurements of volumes and capacities that you take from the graphs.
•
Air pressure changes in the environment during the measurement period can
influence the sensor readings. Sources of such pressure changes include
doors opening or closing, heating/cooling/ventilation systems starting or
stopping, and air movement within the testing room. In most cases
environmental pressure variation is tolerably low over the typical 30-second
test period.
•
The sensor calculates Total Flow by integrating the measured Flow Rate over
time. Because of this time integration, a very small offset in the Flow Rate
measurement may result in a noticeable upward or downward trend in the
baseline of the Total Flow (or Lung Volume) data. This trend usually does not
have a significant effect on the volume and capacity measurements taken
from the graph, since each measurement is made between two data points
recorded within a few seconds. In the data collection software you can
eliminate the trend with this calculation:
Total Flow = integral((1 - inrange(0, .03, abs(smooth(10, R)))) * R)
•
Define R as the Flow Rate. Use the calculated data in place of the data
directly from the sensor. If the trend is still apparent, increase the “.03”
parameter so that it is slightly larger than Flow Rate offset.
Troubleshooting
Problem
Solutions
Drift or fluctuation in the
baseline of Total Flow or Lung
Volume
Slow drift (less than 0.3 L in 30 s) is insignificant and can be ignored.
Protect the mouthpiece from movement, air currents and pressure changes while the
WAIT indicator is blinking.
Do not move the electronics enclosure during the entire test.
Use the calculation described above.
Large shift in baseline of Total
Flow or Lung Volume after
forced expiration
Use a nose clip or have the subject pinch his or her nose to prevent airflow through
the nose.
Ensure a good seal of the subject's lips around the mouthpiece.
Replace the mouthpiece with an unused one.
Unrealistically high Total Flow
or Flow Rate readings
Protect the mouthpiece from movement, air currents and pressure changes while the
WAIT indicator is blinking.
Replace the mouthpiece with an unused one.