Using Sensors to Measure Breath and Respiration

High-quality sensors integrated in respiratory devices are designed to measure the smallest flow rates around the zero point of the respiratory flow, and these sensors can also detect flow rates of several hundred l/minute.

Highly Reliable Flow and Pressure Sensors for Respiratory Devices

Highly Reliable Flow and Pressure Sensors for Respiratory Devices. Image Credit: First Sensor

As a strategic partner to medical product manufacturers in the field of breathing and respiration, First Sensor develops and manufactures highly reliable sensors as well as customized sensor systems. The company therefore complies with the high requirements for medical products in accordance with the EN ISO 13485 certification.

Respiratory Devices

When controlling or triggering high-quality respiratory devices, a vital feature is the early detection of the patient’s inhalation phase through a flow trigger. This is the only way by which the device can assist a spontaneous breath with a preset overpressure and at the same time keep the patient’s respiratory effort to a minimum. In addition to this, the measurements should be highly accurate across the entire flow range for various treatments so that the patient’s respiratory pattern can be detected reliably. In current respiratory devices, a highly dynamic differential pressure sensor or a highly sensitive thermal mass flow sensor often monitors the entire respiratory activity and the spontaneous breathing effort of the patient.

Sensor Solutions for Respiratory Devices

First Sensor offers rapid and highly sensitive thermal mass flow sensors as well as customized versions of its flow-based LMI/LDE/LME differential pressure sensors with resolutions of 0.01% in the lower pressure range and simultaneously dynamic measuring ranges greater than 10,000. These unique sensors are capable of detecting the smallest flow rates around the zero point of the respiratory flow and measuring flow rates of several hundred l/minute. In addition to these products, First Sensor also develops and manufactures custom-made multi-sensor modules as a simple plug-and-play solution for respiratory devices. Integrated with multiple sensors, the modules form fully calibrated and tested systems with definite interfaces and signal processing.

Sleep Apnea Therapy Devices

Pressure sensors integrated in controlled CPAP devices continuously monitor the therapy pressure and thus enhance the quality and comfort of the treatment. A centrifugal blower generates a slight overpressure of a few millibars which is delivered to the patient through a respiratory mask and a tube system. However, the patient’s breathing influences the set therapy pressure of the CPAP device, leading to increased breathing effort for the patient and thus reduced quality of therapy.

Hence, higher-quality devices should be used as these are integrated with a precise pressure sensor that constantly compares the exact pressure value against the specified target therapy value. Following which, the blower output can be dynamically controlled to offset the pressure deviations quickly. Therefore, the pressure stability is an important quality feature and also a vital comparative parameter of controlled CPAP devices.

Sensors with High Resistance to Anesthetics

Sensors with High Resistance to Anesthetics. Image Credit: First Sensor

Sensor Solutions for Sleep Apnea Therapy Devices

The HCE and HDI series of pressure sensors from First Sensor track the pressure value result at the device output or in the respiratory mask. These sensors can detect pressure deviations in fractions of a millibar because of their excellent sensitivity and accuracy. Along with powerful blowers and the latest control electronics, the fast response time of the sensors in the millisecond range allows pressure fluctuations to be compensated quickly.

Anesthetic Devices

Anesthesia respiratory devices or anesthetic devices administer a mixture of nitrous oxide, oxygen, air and anesthetic (e.g. desflurane, sevoflurane or isoflurane) to the patient. Using a vaporizer in the anesthetic device, the volatile anesthetics are added to the respiratory air in precisely defined concentrations. Both flow and pressure sensors monitor the line pressures in the anesthetic device together with the expiratory and inspiratory volume flows, ensuring that the patient receives the gas mixtures that are defined by the Anesthetist in the right concentration and with the required set volume and pressure.

Sensor Solutions for Anesthetic Devices

Differential pressure sensors or thermal mass flow sensors are available from First Sensor to measure expiratory volume and inspiratory volume and pressure in the respiratory unit of the anesthetic device. First Sensor has also developed exclusive versions of its piezoresistive silicon pressure sensors (for instance the HCE and HCLA series) for use with anesthetic gases. These devices have excellent resistance to anesthetics such as desflurane, sevoflurane or isoflurane.


In the case of spirometers, special pneumotachographs (e.g. according to Lilly or Fleisch) are used to determine the respiratory flow using differential pressure sensors. Normally, the patient’s breath flows via an orifice or a laminar flow element with a very small flow resistance leading to a minimal pressure drop across the element, which is a measure of the respiratory flow rate, i.e., respiratory volume per time. It is possible to log these differential pressures with highly accurate sensors and transform them into an electrical signal.

The flow resistance should be kept as low as possible to prevent unnecessarily burden on the respiration of the patient. If respiratory flows are about 7 l/second with forced expiration and are approximately 0.1 l/second during spontaneous respiration, the differential pressures produced through the flow element will thus be very low – in the range from below 100 Pa to several thousand pascals (100 Pa = 1 mbar). Highly sensitive differential pressure sensors are needed to measure low respiratory flows with accuracies of 1% and also ensure measurements over dynamic ranges of greater than 10,000. The sensors must also meet stringent specifications with regard to resistance to dirt and moisture.

Sensor Solutions for Spirometers

First Sensor offers LMI/LDE/LME ultra-low pressure sensors that are perfect for flow rate measurement using the differential pressure method. The new sensor layout with a compact flow channel on the chip level allows highly sensitive measurement of ultra-low pressures from 25 Pa (0.25 mbar) full scale with excellent accuracy and ultra-high resolution.

Ultra-low Pressure Sensors Measure Airflows in Spirometers

Ultra-low Pressure Sensors Measure Airflows in Spirometers. Sensors with High Resistance to Anesthetics. Image Credit: First Sensor

In addition, the semiconductor technology facilitates compact, stable and cost effective designs. The LDE/LME/LMI ultra-low pressure sensors are highly insensitive to dirt and moisture because of the minimal air flow through the sensors. Finally, connecting filters or tubes do not have any negative impact on the measuring accuracy.

Products include:

  • HCL Series: Temperature compensated low pressure sensors
  • HCLA Series: Low pressure sensors with integrated signal conditioning
  • LDE/LME/LMI Series: Ultra-low pressure sensors based on flow measurement
  • Customized sensors, modules and systems

This information has been sourced, reviewed and adapted from materials provided by First Sensor AG.

For more information on this source, please visit First Sensor AG.


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