Low-Cost Differential Pressure Spirometry for Emergency Ventilator Tidal Volume Sensing

Edmunds, J.; Bustamante, M. J.; Raymond, S. J.; Camarillo, D. B.; Piech, D. K.; Schor, J. S.; Maharbiz, M. M.

COVID-19 has become a significant burden on the healthcare systems in the United States and around the world, with many patients requiring invasive mechanical ventilation (IMV) to survive. Close monitoring of patients is critical, with total volume per breath (tidal volume) being one of the most important data points. However, ventilators are complex and expensive devices, typically in the range of tens of thousands of US dollars, and are challenging to manufacture, typically requiring months. Solutions which could augment the ventilator supply rapidly and at low cost in the United States and elsewhere would be valuable. In this paper, we present a standalone tidal volume measurement system consisting of a D-Lite spirometer, pressure sensor, microcontroller, and tubing with a cost of parts less than $50 USD. We also provide a model to predict the error in tidal volume measurements based on the pressure sensor used and the flow during ventilation. We validate this system and show that the tidal volume accuracy for flows above 10L/min was within 10%. We envision this system being used to increase the ventilator supply in resource-constrained settings.