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

Abstract

Background: 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.

Methods: 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.

Results: Filtration efficacy is highly dependent on inhalation flow rate and nozzle-to-plate distance. A high-performance therapeuticwindow 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.

Conclusion: The computational results validate the feasibility of a single, inhalation- actuated valve that integrates selective therapeutic aerosol filtration with diagnostic PEFR monitoring. This design represents a significant step towards developing more personalized, effective, and user-friendly devices for managing chronic respiratory diseases.