B) METHODS: A survey of currently available MDI spacers was conducted with focus on the methods employed to assist users to execute a constant, predefined inhalation flow rate. Most of the models have a flow rate cuing device in the form of a rate-sensitive reed valve (a whistle) that sounds when a specific flow rate (0.5 Liters/second) is reached or exceeded. Measurements were made of available spacer performance. Repeated measurements of inconsistent airflow through whistle-cued spacers demonstrated the need for an improved method of inspiratory flow rate regulation. A valve independent of inspiratory effort was developed as an alternative flow regulator to the whistle-cuing of excessive flow rates.
C) RESULTS: Seven spacers incorporating flow rate-sensitive whistles were tested with two common MDIs. The MDI/sleeve geometries were significantly different resulting in large differences in aerosol flow rates to the patient at the sound of the whistle. For the larger sleeves, these rates were 50% to 100% greater than the design intent. The developed valve was tested in a spacer for flow-control performance. Flow rates between 0.45 and 0.5 Liters/second were consistently achieved regardless of inspiratory effort. No cuing was necessary.
D) CONCLUSIONS: Available MDI spacer combinations provide inconsistent aerosol flow rates. The valve described ensures consistent inspiratory flow rates regardless of MDI/sleeve geometry and patient effort.