Fully Printed Variable Orifice Flowmeter with Built-In Temperature Compensation for Application in Mechanical Ventilation

Abstract

Accurate measurement of respiratory gas exchange is essential for mechanical ventilation. Variable orifice (VO) flowmeters address the limitations of traditional designs by using an orifice that adapts the passage area to the flowrate. However, temperature changes during mechanical ventilation affect VO response, requiring additional components for compensation. The fused deposition modeling (FDM) technique offers a solution by enabling the creation of complex geometries and integrating conductive filaments. Despite its potential, FDM application in flowmeter development remains limited. This article presents the design and characterization of a VO flowmeter with built-in temperature compensation designed for flow measurement under different mechanical ventilation settings. A VO in CB-TPU is directly integrated into the duct to transduce the flowrate into a pressure drop, while simultaneously estimating the fluid temperature. VOs designed with different thicknesses (i.e., 0.4, 0.6, 0.8, and 1.0 mm) are tested to investigate how this parameter influences the relationship between flowrate and pressure drop. In addition, it focused on the advantages of using CB-TPU for estimating the gas temperature to compensate temperature influence on the estimated flowrate. The secondary element consists of a differential pressure transducer characterized by a diaphragm strain gauge made of CB-TPU and silicone rubber.