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15 Monitoring Airway Flow, Volume and Pressure Zero Calibration
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• A volume waveform as displayed below on the left may be an indicator of an air leak:
In general, if MVexp or TVexp are significantly smaller than MVin or TVin, the tubing should be
checked for leaks.
Zero Calibration
The zero calibration maintains the accuracy of the spirometry waves and numerics by regularly
compensating for drifts within the measurement section. It is performed automatically without user
interaction and takes about 2 seconds to complete. The automatic zero calibration is normally carried
out every ten minutes. During warm-up or when the ambient pressure changes, this interval may be
reduced to two minutes.
During the zero calibration the waveform is flat but the numerics remain on the screen. Typically, a
zero calibration is started at the beginning of a respiration cycle, therefore a waveform may begin
normally and then immediately become flat for the time of the zero calibration.
Automatic Purging
A double lumen connecting line (tubing) connects the flow sensors to the patient monitor. The
M1014A Spirometry Module includes an automatic and manual purge feature which provides a flush
of room air to keep the sensor tubing free from water condensation and patient secretions. This feature
is available for the adult, pediatric, and neonatal modes. The purge will begin with the exhalation
portion of the ventilator cycle.
NOTE • During the purge cycle the pump will be heard
• If the purge does not sufficiently clear the flow tubing lines, the flow sensor should be replaced
• With each purge cycle, a zero calibration is automatically performed
Abnormal waveform due to leak
Normal waveform
Zero Calibration