Labs Idea #6: Smart Inhaler

Author: Sensirion Innovations Team
January 2018

Motivation/Summary

Conventional "non-smart" metered dose inhalers (MDIs) or dry powder inhalers (DPIs) against asthma, COPD and other diseases suffer from limitations such as unreliable and inconsistent drug delivery, lack of dose confidence and no compliance monitoring. Monitoring of inspiratory flow and volume in smart inhalers overcome these limitation, leading to less waste of costly drugs and improved patient outcomes.

Approach/Measurement

Sensirion's miniaturized differential pressure sensor SDP3x is a semiconductor MEMS version of the traditional hot wire anemometer. It is easily integrated into a metered dose or dry powder inhaler to accurately measure the inspiratory flow passing through the inhaler and into the patients' lungs (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 differential pressures and therewith accurately measure the flow passing through the inhaler, independent of inhaler type (high resistance or low resistance MDI or DPI).

Figure 1: Sketch of SDP3x integrated into inhaler

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

The measurement of an example inspiratory flow profile is presented in Figure 3. Inhalation duration, flow profile, volume (by integrating over the inhalation profile) as well as many other quantities such as the peak inhalation rate or volume can easily be extracted from the curves shown in Figure 3 and 4.

Figure 3: Example of inhaled flow profile measured with SDP3x using a generic inhaler

Figure 4: Re-plotting data of Figure 3 with inhaled flow rate vs. inhaled volume.

Conclusion

The measurement results demonstrate that Sensirion's SDP3x differential pressure sensor is well suited to measure the inspired air flow in smart inhalers. The high sensitivity of the SDP3x allows highly accurate flow measurement across different inhaler types. Specifically, the SDP3x integrated into inhalers allows to measure:

patient inhaled correctly (according to instructions) through the inhaler
inhalation reached the defined peak flow or volume and total inhaled volume
inhalation flow characteristics

Implementation

To build a smart inhaler (Figure 5) the Sensirion differential pressure sensor SDP3x series (Figure 6) can be sourced from distributors listed on the Sensirion website. Communicate with the digital sensor over I²C according to the explanations in the SDP3x series datasheet or use the appropriate evaluation kit.