For patients with breathing difficulties, a lung function test with a so-called spirometer is recommended. Professional devices at the doctor's office are usually large and expensive. Always on the lookout for ways in which our components can contribute to innovative electronics, we thought about how a small compact device could be realized. It should be suitable for regular use and monitoring by the patient at home. 

A spirometer is a medical device that can be used to test a patient's lung function. It enables the assessment of respiratory volumes and flows by measuring the amount and speed of air that is inhaled and exhaled by the lungs. These measurements are important for the diagnosis and monitoring of respiratory diseases such as asthma, COPD (chronic obstructive pulmonary disease) and other lung dysfunctions. 

A spirometer typically consists of a mouthpiece into which the patient breathes in and out, and which can record respiratory volumes and flows using suitable sensors. These are then interpreted and stored by an electronic circuit. The data is then visualized either on a device-integrated display or transmitted wirelessly via Bluetooth or WiFi to a suitable display device such as a smartphone or tablet. Wireless transmission via the mobile phone network to a cloud, which could be accessed by the attending physician, for example, is also an option.  

Modern spirometers generally only measure the flow velocity and then draw conclusions about the lung volumes by integrating them. A differential pressure flow meter determines the flow velocity via pressure differences in the breathing tube when air flows through the lamellae. It is initially very accurate but loses precision over time due to contamination of the lamellae by the moisture in the breathing air. 

We can therefore recommend the following sensors: The WSEN-PDUS differential pressure sensor is ideal for monitoring the air flow. The WSEN-PDUS offers a measuring range of ±10 kPa (±100 mbar) with a resolution of 15 bits. With dimensions of 13 x 8 mm2, it is compact enough for installation in a mobile device. 

The WSEN-HIDS humidity and temperature sensor can be used to monitor the humidity in both the breathing air and the ambient air in order to determine the contamination of the fins in the breathing tube. With dimensions of 1.5 x 1.5 x 0.5 mm3 , the WSEN-HIDS is very small, outputs humidity and temperature values in 16-bit format and has an I2C interface.  

We also have suggestions for the wireless connection for transmitting the results. The Proteus-III or Proteus-e modules can be used for data transmission via Bluetooth LE 5.1. Proteus-III is based on the nRF52840 chip from Nordic with an output power of 6 dBm. The mobile spirometer can be operated and controlled from a mobile device using an app via the Bluetooth connection. It is also possible to install firmware updates. Proteus-e is based on the nRF52805 chip from Nordic with an output power of 4 dBm. This allows the handheld spirometer to be operated from a mobile device via an app. 

There are two options for connecting the mobile spirometer to a cloud: 

With the Calypso WiFi module, for example, the spirometer can be integrated into a WLAN, which can make the data available to local participants as well as forward it to a cloud via an Internet connection. Calypso supports the IEEE 802.11b/g/n standards at 2.4 GHz, has an output power of 18 dBm and complies with the latest security standards. 

The Adrastea-I mobile radio module, which supports both LTE-NB.IoT and Cat.M1 standards and also allows positioning via GNSS, is suitable for direct cloud connection. 

Of course, a handheld spirometer also needs a suitable power supply. Developers can save themselves work here by using highly integrated MicroModules from the MagI3C series from Würth Elektronik. The MagI3C-VDMM series (Variable Step-Down MicroModules), which operate with input voltages of 2.5 V to 36 V and can typically supply output voltages of 0.6 to 6 V, would be suitable for a spirometer with battery operation. The output currents range between 0.3 and 6 V.

A more detailed version of this spirometer concept can be found here: