Bidirectional Venturi Flowmeter with Capacitive Foam Sensing for Spirometry Measurements

Measuring pulmonary function in patients who suffer from respiratory illnesses is crucial to diagnose and monitor lung conditions. Spirometry is a common tool used to measure lung capacity and diagnose common respiratory illnesses, such as asthma and chronic obstructive pulmonary disease (COPD). Amid challenging times for global healthcare systems, such as the current COVID-19 pandemic, medical instrumentation access is limited and, in most cases, spirometry is restricted only to those who require decisions for immediate treatment. We developed a low-cost 3-D printed symmetrical venturi tube capable of measuring bidirectional flow. The tube wall is embedded with three capacitive foam sensors, capable of detecting the range of pressure from respiratory cycles, providing a differential pressure measurement in two directions to monitor the airflow during in-/exhalation breathing. Custom circuit boards were designed to transmit pressure signals via frequency modulation to mitigate signal artifacts and improve sensitivity. This novel, reusable spirometer design allows for ease-of-use and will increase accessibility for point-of-care monitoring of respiratory illnesses.