Z-Track™ Technology
Every breath in a spirometry test produces a pressure waveform that is evaluated against the sensor’s zero baseline to calculate lung function. When zero drift shifts that baseline between breaths, the calculated values shift with it, and a patient’s results can cross a clinical diagnostic threshold they would not otherwise reach. Z-Track Technology continuously eliminates zero drift, ensuring an accurate zero baseline before each breath throughout the full test sequence.
What is Z-Track Technology?
A spirometry test evaluates lung function by measuring airflow during a controlled series of breathing maneuvers. The patient breathes into a mouthpiece, and the spirometer captures the pressure waveform generated with each breath. From these waveforms, the instrument calculates clinical parameters such as forced expiratory volume in one second (FEV1) and forced vital capacity (FVC), then compares them with reference standards to determine whether lung function is normal or indicates conditions such as COPD or asthma. The accuracy of the clinical outcome depends directly on the accuracy of the pressure measurement for each breath.
A spirometry test consists of multiple breaths taken in sequence, with a brief pause between each. During these pauses, when there is no airflow and the differential pressure should be zero, the sensor’s output does not necessarily read exactly zero. Zero drift, driven by thermal effects and a time-varying offset in the sensing element, continuously shifts the sensor’s baseline. When the next breath begins, the measurement starts from this shifted baseline rather than true zero. The pressure waveform for that breath is offset by the drift amount, and the clinical values calculated from it carry that error. Across a full test with multiple maneuvers, zero drift can compound into a systematic bias large enough to move the calculated FEV1 or FVC values across a clinical diagnostic threshold.
The clinical stakes of that shift are significant. Spirometry diagnostic thresholds are defined with high precision, and patients whose true values are near a threshold are most vulnerable to zero-drift-induced misclassification. A patient whose actual FEV1/FVC ratio falls just above the COPD threshold may be classified as having COPD if zero drift introduces enough bias into the measured values. The same patient, tested on a sensor with Z-Track Technology, would be correctly classified. The consequence is not a minor measurement inconvenience; it can determine whether a patient receives treatment for a condition they do not have or fails to receive treatment for one they do.
Z-Track Technology addresses the between-breath drift problem with a proprietary algorithm that continuously tracks and corrects the sensor’s zero offset. Between breaths, the algorithm returns the sensor’s baseline to an accurate zero before the next measurement begins. No manual recalibration is required, no additional hardware is needed, and the correction is applied transparently within the measurement sequence. Each breath starts from a known, accurate zero reference, regardless of its position in the test or how much time has elapsed.
For handheld spirometers, where device orientation changes with the patient and the clinician, position-induced offset compounds the zero drift problem. The SP210 model features best-in-class position insensitivity, ensuring that changes in sensor orientation do not introduce additional zero error. Combined with Z-Track, the SP210 delivers consistent zero stability and accurate measurements across handheld and desktop spirometry configurations, regardless of device orientation.
Z-Track Technology Video
Availability
Z-Track Technology is exclusive to the SP Series: SP110, SP160, and SP210.
Z-Track Technology FAQ
What causes zero drift in a spirometry sensor, and why does it occur between breaths?
Zero drift in a differential pressure sensor arises from thermal effects on the sensing element, time-varying mechanical stress in the package, and component aging. In a spirometry environment, temperature changes from patient breath, ambient conditions, and device handling all contribute. The result is a slow, continuous shift in the sensor’s zero output that is negligible over a fraction of a second but meaningful over a multi-breath test, where each breath depends on the accuracy of the preceding zero baseline.
Why is between-breath zero drift clinically significant rather than just a measurement inconvenience?
Spirometry diagnostic thresholds are defined in absolute terms. For example, an FEV1/FVC ratio below a specific value classifies a patient as having obstructive lung disease. A patient whose true ratio is close to that threshold can be misclassified if zero drift introduces sufficient systematic bias into the measured pressure values. The direction and magnitude of the drift determine whether the result is pushed above or below the threshold, but in either case the outcome is a clinical decision that does not reflect the patient’s actual lung function.
Does Z-Track require any hardware changes to the spirometer design?
No. Z-Track is implemented entirely within the SP Series sensor as a proprietary algorithm. It requires no external valves, equalization hardware, or additional components, and it does not require any changes to the spirometer’s mechanical design. The sensor outputs corrected data via its standard interface, and the correction remains transparent to the host system.
Does Z-Track affect any sensor parameters beyond the zero baseline?
Z-Track corrects only the zero offset. It does not change span calibration, linearity, or sensitivity. All other performance specifications remain governed by the factory calibration for the active pressure range, and the total error band is unaffected by Z-Track operation.
Is Z-Track available on any Superior Sensor product other than the SP Series?
No. Z-Track Technology is exclusive to the SP Series: the SP110, SP160, and SP210. These products are designed for spirometry and precision medical pressure measurement applications where between-breath zero stability is a primary performance requirement.