Wireless Spirometers Based on Integrated Thermal Flow Sensors

Reference to the above figure, in combination with a smart phone a spirometer is used to generate a flow-volume loop for a man who is required to measure his forced vital capacity.

As shown in the graph on the screen of the smart phone, a normal flow-volume loop begins on the x-axis (volume axis): at the start of the test both flow and volume are equal to zero. After the starting point the curve rapidly mounts to a peak: peak (expiratory) flow.

After the forced expiratory volume in one second (PEF) the curve descends as more air is expired. A normal, non-pathological F/V loop will descend in a straight or a convex line from top of PEF to bottom of forced vital capacity (FVC). The forced inspiration that follows the forced expiration has roughly the same morphology, but the peak inspiratory flow (PIF) is not as distinct as PEF.

The flow-volume loop can take on many distinguishable shapes that correspond to a certain type of pathology. Using the flow-volume loop displayed by the smart phone, the following pathologies can be easily and correctly diagnosed.

• normal spirometry,
• pathological spirometry,
• obstructive lung disease,
• restrictive lung disease,
• mixed lung disease,
• obstruction of the large airways,
• exercise induced asthma.

The spirometer in the above figure utilizes an integrated thermal flow sensor provided by POSIFA Microsystems, which is a famous MEMS company located in Silicon Valley in the United States. The integrated thermal flow sensors exhibit short response time (1ms), low power consumption (30mw), and high accuracy (0.5%). It represents an attractive solution for portable spirometers in home-care applications.

The spirometer further consists of a CC2650 ultra-low power wireless MCU, which can provide a wireless connectivity solution supporting multiple standards to enable faster internet designs. With this device the spirometer can be managed being small, inexpensive and up to years of battery life.

The smart phone is not only to visualize a flow-volume loop based on the data send by the spirometer, but also con­nect the spirometer to the cloud. The cloud is a great place to back things up, because the spirometer has lim­ited stor­age and unre­li­able flash mem­ory. Plus, the spirometer could get lost, dam­aged, or stolen. The cloud is great for data pro­cess­ing because pro­cess­ing in the cloud reduces the load on the micro­proces­sor. This saves power and might reduce the per­for­mance require­ments of the micro­proces­sor. Furthermore, data that is already in the cloud can be shared quickly and eas­ily by many users.

The flow-volume loop is a remarkably versatile and informative measurement, which can identify a range of diseases including chronic obstructive pulmonary disease (COPD). COLD is a type of obstructive lung disease characterized by chronically poor airflow. It typically worsens over time. The main symptoms include shortness of breath, cough, and sputum production. Most people with chronic bronchitis have COPD. Used together with other clinical features, the flow-volume loop can substantially improve assessment of the patient and their long-term management.

Worldwide, COPD affects 329 million people or nearly 5% of the population.^[6] In 2013, it resulted in 2.9 million deaths up from 2.4 million deaths in 1990. The number of deaths is projected to increase due to higher smoking rates and an aging population in many countries.^[8] It resulted in an estimated economic cost of $2.1 trillion in 2010.