Test & measurement This makes the Sensirion SDP3x flow sensor
series the flow sensor solution of choice for accurately measuring the inhalation flow profile in inhalation devices.
OutlOOk Of flOw MeasureMent in sMart inhalers
Figure 5. Typical spirometer plot of flow rate versus inhaled volume. The inspired vital capacity (IVC) is the total inhaled volume as the flow rate returns to zero at the end of the inhalation.
Adding a diagnostic unit to the drug delivery device that the patient is already familiar with is a powerful tool in asthma and COPD disease management. Improper inhalation technique leads to decreased efficacy through reduced deposition of drug in the lungs, which in turn leads to increasing disease severity and thus a worse patient outcome and an increase in healthcare costs. The solution of guiding the patient and providing direct feedback as well as supporting the patient in controlling the disease and increasing adherence have already been shown to improve patient outcomes by current connected drug delivery devices. Thus, robust and accurate flow measurement is
Figure 6. Peak inspired airflow (PIF), inspired vital capacity (IVC) and airway resistance (RAW) monitored over time, providing valuable feedback to the healthcare professional and the patient.
key regulatory requirement for all inhaler clip-ons demands that the flow path of the inhaler remains unaltered in order to ensure that it does not interfere with the existing inhaler device function. In order to demonstrate how accurate flow
measurement through an inhaler can be realized without interfering with the flow path, a functional inhaler clip-on has been developed by Sensirion. Figure 7 shows the 3D-printed inhaler clip-on containing the Sensirion flow sensor SDP3x as well as a Bluetooth low energy communications chip and a battery power source. It is notable that the inhaler housing has not been altered in any way and the flow measurement principle relies solely on the Venturi/Bernoulli principle at the inhaler inlet. The calibrated inhaler airflow shows excellent agreement to an external flow reference and was used for obtaining the flow profiles depicted in this article. The unaltered and unobstructed inhaler flow
path design is enabled by the extreme sensitivity of the Sensirion MEMS-based (micro electro mechanical system) flow chip solution utilised in the SDP3x flow sensor series. This technology is based on the microthermal flow-through principle, the next generation hotwire flow sensor
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technology that has been successfully used in medical ventilators for decades. In clip-ons for existing inhalers as well as newly developed inhalers, the advantages of Sensirion’s CMOSens flow chip technology can be summarised as:
Highest sensitivity down to hundredths of a Pascal
High temporal and pressure/flow accuracy
Proven device in the medical and automotive industry
Robust against being dropped and ultra-sonic welding process steps
Inherently robust against external disturbances by the two-port design
Low power consumption for portable and battery operation
World’s smallest commercially available flow sensor
March 2022 Instrumentation Monthly
an important feature towards better disease management and patient outcomes and is already realisable today. The high percentage of patients suffering from asthma or COPD and misusing their inhaler when a life free of complaints would generally be possible with proper disease management will continue to drive innovation for connected drug delivery. An increasing number of companies are implementing digital technologies in their products already today to provide an enhanced method of managing asthma and COPD as well as improving the effectiveness of medication. Supporting the patient with the optimal treatment of their disease, not solely as a simple medical tool but as a companion device to remind, coach and provide relevant insight into the treatment and the course of the disease, is the direction in which the industry is advancing.
Sensirion
sensirion.com
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