Boosting Spirometry Accuracy with Advanced Pressure Sensors

Spirometry Sketch

Spirometry Market

Spirometers are non-invasive medical devices primarily used for evaluating and diagnosing lung conditions by measuring various parameters related to the volume of air inhaled and exhaled. Spirometers are widely used in respiratory health examinations, lung function tests, preoperative and postoperative evaluations, and are often integral to pulmonary rehabilitation and physical therapy.

Spirometers are crucial in diagnosing various respiratory diseases such as chronic obstructive pulmonary disease (COPD), asthma, chronic bronchitis, pulmonary fibrosis, and cystic fibrosis. Tests determine the severity of these lung conditions and track the progress of disease treatment. Additionally, spirometers help identify potential lung disorders in people who are at risk, including smokers, industrial workers, or individuals with exposure to harmful airborne substances.

Spirometers measure several key metrics, including:

  1. Forced Vital Capacity (FVC) measures the largest amount of air one can exhale forcefully after taking in the deepest possible breath. A lower than normal FVC reading indicates restricted breathing.
  2. Forced Expiratory Volume (FEV1) measures the air a person can forcefully blow out in the first second after full inhalation. This reading assesses the severity of the breathing problem – the lower the FEV1, the more significant the obstruction.
  3. Maximum Voluntary Ventilation (MVV) measures the maximum amount of air that can be inhaled and exhaled within one minute.
  4. Forced Expiratory Flow (FEF) is the flow or speed of air coming out of the lungs during the middle portion of the exhale.
  5. Peak Expiratory Flow (PEF) is the maximum flow of air one can exhale in a short burst after full inhalation. It is typically used to monitor asthma.
  6. Tidal Volume (TV) is the amount of air inhaled or exhaled when in a resting condition.
  7. Total Lung Capacity (TLC) is the maximum volume of air present in the lungs when inhaling.

The FEV1/FVC Ratio is a critical measure. This ratio should be approximately 70 – 80% in healthy adults, but it does decline with age. In obstructive diseases (asthma, COPD, chronic bronchitis, emphysema), FEV1 is diminished because of increased airway resistance when exhaling; the FVC may be decreased as well, due to the premature closure of the airway in expiration, just not in the same proportion as FEV1. In restrictive diseases (such as pulmonary fibrosis), the FEV1 and FVC are both reduced proportionally, and the value may be normal or even increased due to decreased lung compliance.

Spirometers thus play a pivotal role in respiratory medicine, serving diagnostic and therapeutic purposes. They facilitate early detection, timely intervention, treatment tracking, and prognosis assessment for various lung diseases. Therefore, they are a significant tool in outpatient and hospital settings, benefiting clinicians, researchers, and patients.

Picture of a spirometer connected to a computer

Figure 1 – Image of Spirometer connected to PC

The Role of Differential Pressure Sensors in Spirometers

Although various types of flow-sensing spirometers exist, including turbine, thermal, and ultrasonic models, this blog post will focus on differential pressure-based spirometers. These particular spirometers are widely utilized and renowned for their precision in measurements.

A differential pressure sensor utilizes a thin diaphragm equipped with strain-sensitive and compression-sensitive resistance structures to convert pneumatic pressure values into proportional electrical signals. The measurement of pressure relies heavily on the diaphragm, which is deflected by air pressure during a patient’s inhalation and exhalation from the spirometer. The resulting deflections are then converted into electrical signals, in the form of analog output voltages, that correspond to the applied differential pressure as detected by the diaphragm.

However, differential pressure sensor-based spirometers pose potential challenges. Pressure sensors exhibit sensitivity to various external factors, including noise, humidity, temperature, atmospheric pressure, and the physical positioning or orientation of the device. Another notable challenge differential pressure sensors face, especially when gauging low-pressure airflow, is the potential necessity for recalibration. Over time, these sensors tend to deviate from their initial zero reading.

Differential pressure sensors that mitigate the influence of noise, remain unaffected by changes in position or orientation, maintain a stable, consistent zero value, deliver the utmost accuracy in readings, and empower healthcare professionals to diagnose lung performance more effectively.

Superior Sensor’s Technology Advantage

Superior Sensor’s cutting-edge NimbleSenseTM architecture stands out as the first-of-its-kind integrated platform in the industry. Incorporating a highly sophisticated pressure sensing system eliminates noise from external factors, providing a very high signal-to-noise ratio. In addition, the unique architecture’s building blocks provide exclusive features designed explicitly for spirometry. Superior’s SP Series differential pressure sensors utilize advanced technology to offer numerous benefits to critical care medical devices and spirometry.

Z-TrackTM Auto Zero

Superior’s proprietary Z-Track technology virtually eliminates zero drift by maintaining minimal zero-point deviation with consistent results regardless of elapsed time. For more details on Z-Track technology, read the Z-Track blog post.

Position Insensitivity

Superior’s unique dual-die implementation with the SP210 sensor maintains consistent and highly accurate handheld readings regardless of the physical orientation of the spirometry device. Rated with a positional sensitivity to within 0.25 Pa, the SP210 is an industry leader concerning position insensitivity.

Highest Levels of Accuracy

Sensor accuracy is critical as the difference between an effective and ineffective treatment plan can depend on the precision of the diagnosis. A slight difference in measurement can alter the dosage or even the type of medication prescribed to a patient. Superior’s SP Series spirometry sensors have the industry’s leading accuracy to as close as within 0.05% of the selected pressure range.

Fastest Warm-up and Response Times

The spirometer’s warm-up time is important for time-critical situations. The SP Series eliminates warm-up time concerns, as the device is ready in just 60 msec. In addition, the amount of time it takes the pressure sensor to update its measurement data is just as vital. The faster you receive updated pressure measurements, the more accurate your spirometry readings. While user-configurable, Superior’s sensors support update rates as fast as 2 msec.

Lowest Noise Floor

External noise can affect spirometer accuracy and performance. Superior’s pressure sensors utilize our integrated advanced digital filtering technology to eliminate the noise created by these factors before they impact system performance. Thus, the noise is eliminated before it becomes an error signal that can lead to inaccurate lung measurements.

Low Power Consumption

Many spirometers are self-contained handheld devices connected to a computing device via a USB port, so power consumption is another important factor in overall device performance. With power consumption as low as 5 mA, the SP Series will not adversely impact the battery life of even the most sophisticated spirometry equipment.

Spirometry sketch

Figure 2 – Sketch of a patient using a handheld spirometer


Spirometers play a crucial role in diagnosing and managing various lung diseases. Accurate diagnosis requires spirometry products equipped with high-performance differential pressure sensors to precisely assess lung function. These sensors need to filter out noise and maintain accuracy despite elapsed time. Furthermore, handheld units must deliver consistently accurate readings during use, regardless of orientation.

Superior Sensor’s innovative technology, centered around our proprietary NimbleSense architecture, offers a range of distinctive features that enable medical device manufacturers to set their products apart in a competitive market. For comprehensive details on our Spirometry solutions, please visit our product page or contact us for further information.

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