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SUMMARY REPORT

EFFECTIVENESS OF ELECTROMEDIA MODEL 35F(A)

INHALANT ALLERGEN REMOVAL

SUMMARY OF REPORT PREPARED BY THE DEPARTMENTS OF RESPIRATORY MEDICINE & IMMUNOLOGY, WESTERN INFIRMARY, GLASGOW

Introduction and Background

In the UK, as with other temperate regions of the world, house dust mite allergen is the main sensitising allergen associated with allergic asthma. This allergen is common, and controlling exposure is likely to result in considerable clinical benefit. Since the main route of allergen sensitisation in asthma is probably by inhalation then control of the airborne levels of allergen are likely to be important.

The aims of this study on the effectiveness of the Electromedia Model 35F(A) were:-

 

  1. To identify a test system which will lend itself reproducibly to testing alterations in airborne allergen content.
  2. To apply this methodology to testing the Electromedia Model 35F(A)

Test System for Testing Alterations in Airborne Allergen Content

An alternative source of measurable protein to house dust mite allergen was required for testing purposes because of the impracticality of using high levels of potentially sensitising house dust mite allergen. A protein enzyme system was used whose components were considered safe according to Control of Substances Hazardous to Health (COSHH) guidelines.

Conclusions

The Report Demonstrates:-
  1. The development of reproducible method for generating aerosols of measurable protein which is quantifiable and safe.
  2. The use of this method in demonstrating the efficiency of the Electromedia Model 35F (A) in system in reproducibly removing airborne protein with high efficiency.
Professor Neil C Thomson
West Glasgow Hospitals University NHS Trust
Glasgow

Dr Charlie McSharry
Department of Immunology
Western Infirmary
Glasgow

Ms Kirsten McLeod
Department of Respiratory Medicine
Western Infirmary
Glasgow

 


EFFECTIVENESS OF AN AIR PURIFICATION SYSTEM (MODEL 35F)

Introduction and Background

House dust mite allergen is the main sensitising allergen associated with allergic asthma in temperate regions of the world. This allergen is common, and controlling exposure is likely to result in considerable clinical benefit. There have been many attempts to reduce this allergen including barrier methods, acaricides, control of soft furnishings and increasing ventilation, and these have been associated with clinical improvement. Since the main route of allergen sensitisation in asthma is probably by inhalation then control of the airborne levels of allergen are likely to be important. This approach has still to gain general approval however a few studies have shown that using air cleaners has resulted in reduced airborne allergens and clinical improvement [1,2]. The first essential step is to establish a uniform method for testing and demonstrating the efficacy of an air purification system. The aims of this study are

a) to identify a test system which will lend itself reproducibly to testing alterations in airborne allergen content.
b) to apply this methodology to testing the air purification Model 35F (A).

 

Materials and Procedures

Location, aerosol generation and air sampling
A sealed, uniform, unfurnished room with dimensions 4.05m x 2.62m x 3.62m (volume = 38.4 M3) was used. A nebuliser with an airflow delivery of 8 L/ntin was used to generate a standard aerosol. Air sampling was performed using two air samplers (Casella, model AFC 123) which were calibrated to sample at 2 L/min. The air samplers were fitted with 2.5cm fibre glass or cellulose acetate filters (Micropore Ltd).

Measurement of the protein solutions used as aerosols
House dust mite (Bencard Ltd) and alkaline phosphatase (Sigma UK Ltd) were each dissolved in phosphate buffered saline (PBS) at 1 mg/ml. These were optimum values based on the detection limits of the assay systems. Following various periods of nebulisation the air filters were collected and the adsorbed antigen was solubilised with PBS containing 0.5% Tween-20 detergent (Sigma UK Ltd). The major house dust mite Dermatophagoides pteronyssinus antigen (Der p 1 ) was measured by commercial enzyme immunoassay (ALK Ltd) using the distributor's instructions. Alkaline phosphatase was measured by its specific enzyme activity in converting a clear p-nitrophenyl phosphate (Sigma UK Ltd) substrate into coloured product with an absorbance maximum at 405nm measured by spectrophotometry (Model 6000, Dynatec UK Ltd)

Assessment of air purification unit
The effectiveness of an air purification unit (The Electromedia Model 35F [A]) to remove antigenic aerosols was tested as follows. Airborne protein levels were measured in duplicate filters using the air samplers. Background room air was sampled before antigen was nebulised to give a control limit of normality. Steady-state levels of aerosolised antigen were measured during nebulisation, and the effects of the intervention by the air purification system were tested by concurrently running the system under various conditions. These conditions included running the fan motor with no internal filter, with a fine filter or with a rough filter. In addition the effects of running the system at floor level or mounted at 1 m height on a pedestal were compared.

Results

Using house dust mite allergen
The steady state airborne levels of detectable house dust mite allergen was 2 ug/m] which was the lower limit of the assay resolution therefore it would be impractical to use this allergen preparation to test an air filtration device. This detected level fell below the theoretical levels which should have been attained therefore the Der p I allergen content of the commercial house dust mite preparation was measured. This was 136 ug/n-d which was approximately 1% of the estimated total allergen content of the preparation which was stated to be 12 mg/m]. There was a further potential source of difficulty which related to the nebulisation process on the allergen. Some sample residue from the nebulisation chamber was tested and was found to have a lower detectable allergen than the original material. One explanation was that the Der p 1 is labile and the nebulisation had a denaturation effect on this protein.

Using an enzyme - alkaline phosphatase
An alternative source of measurable protein was required because of the impracticality of using high levels of potentially sensitising allergen. It was decided to use a protein enzyme system, The use of alkaline phosphatase and its substrate para-nitrophenyl phosphate was chosen because these components are considered safe according to COSHH guidelines.

The various components of the system were tested ie. the amount and rate of enzyme to be nebulised, the air sampling time, the type of air filter, the efficiency and stability of the enzyme binding to the air filters and the reversibility of this in order to measure the enzyme.

The optimum conditions were for the enzyme at 1 mg/5rffl PBS to be nebulised completely, usually 15 min and for the air samples to be for 30 min. The binding of enzyme to filter was almost entirely reversible for measurement purposes (table 1) and the amount of enzyme eluted could be quantified by comparison to a standard curve of known amounts of enzyme activity

Table 1. Comparison of enzyme activity measured directly or following nebulisation and elution from an air-sample filter.
Enzyme concentration
(dilution curve)
Direct Filter Eluate
Neat (1 mg/5ml) 3.712 3.634
N/2 3.739 3.644
N/4 3.683 3.644
N/8 3.712 3.625
N/16 3.602 2.272
N/32 2.150 1.289
N/64 1.195 0.790
N/128 0.636 0.440
N/256 0.355 0.242
N/512 0.197 0.198
N/1024 0.143 0.147
N/2048 0.108 0.110
Testing the air purification system model 35F(A)
Using the above protocol, the effectiveness of an air purification system was tested. A steady state level of airborne protein enzyme was established. When the air filtration system was fitted with either a fine or rough cassette filter there was a significant reduction in airborne protein enzyme, and the efficiency was increased marginally when the device was pedestal mounted.

Conclusions

This report demonstrates

a) the development of a reproducible method for generating aerosols of measurable protein which is quantifiable and safe.
b) the use of this method in demonstrating the efficacy of an air filtration system in reproducibly removing airborne protein with high efficiency.

References

  1. Pahdi HS, Simpson A, Custovic A, Woodcock A. The effect of high efficiency particulate air cleaner on airborne cat allergen. Thorax 1997 52 suppl:A3.
  2. Sanda T, Yasue T, Oohashi M, Yasue A. Effectiveness s of house dust mite allergen avoidance through clean room therapy in patients with atopic dermatitis. J Allergy Clin Immunol 1992;89:653-7
Departments of Respiratory Medicine & Immunology
Western Infirmary
Glasgow G11 6NT

 
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