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Biomedical subjects

S W Stein

Publications and source records attributed to S W Stein.

4 recordsLinked to original sources
PubMed1999

A new method to evaluate plume characteristics of hydrofluoroalkane and chlorofluorocarbon metered dose inhalers.

Two concerns raised when comparing metered dose inhalers (MDIs) to other inhalation devices are their relatively high throat deposition and the 'cold-Freon' effect seen in a small number of patients. The cold-Freon effect is presumed to be a result of the cold, forceful MDI plume impacting on the back of a patient's throat. This in vitro study uses a new plume characterization method to determine the spray force and plume temperature of various MDIs. Spray force measurements were made for 28 marketed products consisting of bronchodilators, steroids, press-and-breathe, breath-actuated and nasal inhalers. Results show that chlorofluorocarbon (CFC)-containing MDIs produce extremely forceful and cold plumes. Several hydrofluoralkane (HFA)-containing MDIs produced much softer and warmer plumes, but two HFA products had spray forces similar to the CFC products. Although the type of propellant used can affect spray force, actuator orifice diameter is the most important factor. Data obtained from marketed products and experimental inhalers show that MDIs that have a low spray force also have low throat deposition.

Chlorofluorocarbons↗
PubMed1999

Size distribution measurements of metered dose inhalers using Andersen Mark II cascade impactors.

The performance of Andersen Mark II impactors was investigated theoretically and experimentally. Theoretical calculations were made to assess the impact that differences in jet diameters among Mark II impactors have on size distribution measurements of metered dose inhalers (MDIs). A previous investigation indicated that the jet diameter for stages on Mark II impactors often do not conform to the manufacturer's specifications (Stein and Olson, 1997). For the calculations reported in this paper, only jet diameters that conform to the manufacturer's specifications were considered. The calculations indicate that large differences in the amount of drug collecting on a given stage should be expected among Mark II impactors sampling an identical aerosol-even for Mark II impactors that conform to the manufacturer's specifications. These calculations suggest that it is impractical to analyze size distribution data generated with cascade impactors, such as the Mark II, on a stage-by-stage basis. Experimental measurements of three MDI products were made using three different Andersen Mark II cascade impactors. Measurements of the same product were very consistent for a given impactor, but large differences were observed in measurements of the same product with different impactors. For measurements of QVAR HFA beclomethasone dipropionate MDIs using three Mark II impactors, the amount of drug that collected on Stage 6 ranged from 28.7 to 41.3% of the sampled mass depending on which impactor was used. The theoretical calculations and experimental measurements reported in this paper demonstrate that it is important to consider the limited precision of cascade impactors, such as the Andersen Mark II, when analyzing the size distribution measurements that they provide.

Nebulizers and Vaporizers↗
PubMed1997

Variability in size distribution measurements obtained using multiple Andersen Mark II cascade impactors.

PURPOSE: Andersen Mark II cascade impactors are commonly used for the testing of pharmaceutical aerosols. The reproducibility of size distribution measurements made with various Mark II impactors was assessed theoretically and experimentally. METHODS: Stage cutpoints were calculated for fourteen Mark II impactors based on jet diameter measurements for each stage. The calculated cutpoints were used to predict differences in size distributions measured with various Mark II impactors. Five impactors were exposed to an atomizer-generated oleic acid test aerosol to experimentally verify predicted differences in size distribution measurements among impactors. RESULTS: Stage cutpoints were calculated to vary by up to 0.45 micron for 'identical' stages of different Mark II impactors based on jet diameter measurements. The size distributions measured with various Mark II impactors were shown to be significantly different based on theoretical and experimental observations. For one particular experiment, the amount of material collected on Stage 6 ranged from 26.8 percent of the total sampled mass to 40.9 percent depending on which Mark II was used. Theoretical calculations predicted that the amount of material collected on Stage 6 would vary from 24.0 to 43.5 percent of the total sampled mass among impactors for this experiment. A Similarity Ratio, useful for interpreting the test results, was defined and discussed. CONCLUSIONS: Significant differences in stage cutpoints exist among Andersen Mark II impactors. These differences in stage cutpoints can result in large differences in size distribution measurements made with various Mark II impactors. By measuring jet diameters and calculating stage cutpoints, it is possible to predict the performance of a particular Mark II impactor.

Aerosols↗