Design of a Novel Dual-Function Spacer Valve for Selective Aerosol Size Filtering and Measuring Peak Expiratory Flow Rate

Abstract

Abstract. Variable inhalation flow rates reduce aerosol drug efficacy, while separate devices for therapy and monitoring hinder patient adherence. This study computationally designs a novel, dual-function valve to solve these issues. Operating on inertial impaction, the valve uses a nozzle to create an aerosol jet and a movable plate to force a sharp airflow turn. Larger, high-inertia particles impact the plate, while smaller therapeutic particles remain entrained. Building on an optimized geometry, a computational fluid dynamics (CFD) model characterized valve performance across clinically relevant conditions. The model simulated aerosol transport during low-flow therapeutic inhalation (10–60 L/min) and high-flow diagnostic peak expiratory flow rate (PEFR) exhalation (100–700 L/min). A custom “valve efficacy” metric quantified selective particle filtration based on aerodynamic diameter. Filtration efficacy is highly dependent on inhalation flow rate and nozzle-to-plate distance. A high-performance therapeutic window was identified at 20–35 L/min, maintaining efficacy above 90%. A direct, linear relationship between aerodynamic drag on the plate and the optimal filtration distance was established. This enables a passive, self-regulating mechanism governed by a linear spring. Augmenting this with a second, stiffer spring in series allows the assembly to function as a PEFR meter. The computational results validate the feasibility of a single, flow-actuated valve that integrates selective therapeutic aerosol filtration with diagnostic PEFR monitoring. This design represents a significant step toward developing more personalized, effective, and user-friendly devices for managing chronic respiratory diseases.