The Analysis and Optimization of a Respiratory Flowmeter

This thesis presents an analysis of an instrument which is used to assess respiratory function. This instrument is designed to measure respired gas volumetric flowrate. An instrumentation problem related to physiology is obtaining an accurate, efficient and economic measurement of respiratory gas flowrate in humans and laboratory test animals. This thesis develops the design criteria and the prototypes for optimal pneumotachometers (PTMs) for human and animal application. The PTMs studied are screen type resistive element flowmeters designed to efficiently measure respiratory gas volumetric flowrate at expiration and/or at inspiration. A mathematical model based on a force balance describes the PTM pressure drop across a single fine-mesh, square-weave wire screen. The pressure drop is described as a function of the fluid properties, the screen geometric properties and the PTM geometric properties involved in this phenomenon. Experimental data taken with steady-state gas flow at room temperature are shown to correlate with the mathematical model. This thesis also describes an analog integrator which utilizes a PTM flowrate signal. The PTM and integrator can be used to obtain both respired gas flowrate data and respired gas volume data for clinical and research applications