Labs Idea #14: Improved Puff Sensing of Inhalation Devices
Some inhalation devices use puff sensors to count the number of puffs or detect inhalation. To enhance drug delivery a flow sensor could characterize volume, peak flow and duration of the inhalation.
Sensirion's miniaturized differential pressure sensor SDP3x 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).
Sensirion's differential pressure, respective flow sensor is easily integrated into an inhalation device to accurately measure the inspiratory flow passing through the atomizer or heater before entering the smokers' lungs. Figure 2 depicts an integration example for a large inhaler. For smaller spaces in inhalation devices, Sensirion's CMOSens flow sensor die (with custom package) could be integrated directly into the suction flow passage (Figure 3).
As opposed to diaphragm based differential pressure sensors, Sensirion's CMOSens differential pressure (aka flow) sensor characteristic shows high sensitivity especially at low differential pressures (Figure 4). This allows to reliably measure ultra-low differential pressures and therewith accurately measure the flow passing through the inhalation device.
The measurement of an example inspiratory flow profile of two different inhalating persons is presented in Figure 5 & 6.
Inhalation duration, flow profile, volume (by integrating over the inhalation profile) as well as many other quantities such as the peak inhalation rate can easily be extracted from the curves shown in Figure 5 and 6.
Use Sensirion’s tiny flow sensor to measure inhalation volume much more precisely than with a puff or pressure sensor:
- Measure inhalation dose
- Measure liquid consumption and detect empty atomizer tank
- Characterize & collect user profiles
- Consulting, e.g. give real-time inhalation profile feedback with app
The measurement results demonstrate that Sensirion's SDP3x differential pressure sensor is well suited to measure the inspired air flow in inhalation devices. The high sensitivity of the SDP3x allows highly accurate flow measurement across different type of inhalation styles.
Specifically, the SDP3x integrated into inhalation devices allows to measure:
- puff detection
- duration and amplitude of inhalation
- inhalation flow characteristics
To integrate the small flow sensor (Figure 7) used inside of Sensirion's differential pressure sensor SDP3x series (Figure 8) into inhalation devices please contact Sensirion. For first feasibility tests we propose to use the flow and differential pressure sensor evaluation kit EK-P4 (Figure 9).
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