Labs Idea #12: Breath Detection

Author: Sensirion Innovations Team
February 2018

Motivation/Summary

Non-local breath detection separates electronics from the patient interface which is often a face mask or nasal connection. The separation from the patient requires sensing the patients breath through long and often thin tubing, for example as in the case of nasal cannulas used in supplying the patient with oxygen. The requirements on the sensors are then very high sensitivity at very low flows, a strength of the SDP3x differential pressure sensor.

Approach/Measurement

Sensirion's differential pressure sensor is a semiconductor MEMS version of the traditional hot wire anemometer. The sensing principle is based on thermal conductivity of the gas flowing over the sensor surface (figure 1).

As opposed to diaphragm based differential pressure sensors, Sensirion's CMOSens differential pressure sensor characteristic shows high sensitivity especially at low differential pressures (figure 2). This allows to reliably measure ultra-low flows or differential pressures.

Figure 2: Sensirion sensors are more sensitive at low differential pressures than diaphragm type pressure sensors

A Sensirion differential pressure sensor was attached to the end of a nasal cannula (Figure 3). To enable air flow through the sensor the second port was left open to the ambient. The other end of the nasal cannula was attached to the nose to detect breathing cylces. The sensor output was logged with Sensirion's EK-P4 evaluation kit.

Figure 3: SDP3x differential pressure sensor attached to the end of the nasal cannula

Figure 3: SDP3x differential pressure sensor and nasal cannula

The measurement results demonstrate that Sensirion's differential pressure sensor can be used as breath detection sensor due to high sensitivity even at lowest flows (Figure 4).

Figure 4: Recorded signal of person breathing through mouth (0-10s) and nose (10-20s)

Conclusion

Breath detection with Sensirion's differential pressure sensor is possible through 2m (6.5 feet) long nasal cannula
Inhalation, exhalation and holding breath can clearly be distinguished
Strong signal measured by the SDP3x, even for "mouth only" breathing in which the flow through the nose is minimal

Implementation

Sensirion's SDP3x differential pressure sensor or EK-P4 evaluation kit can be sourced from distributors listed on the Sensirion website.

Patent Information

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