Labs Idea #12: Breath Detection
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.
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.
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.
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).
- 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