SUMMARY
REPORTEFFECTIVENESS 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:-
- To identify a test system which will lend itself
reproducibly to testing alterations in airborne allergen
content.
- 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:-
- The development of reproducible method for generating
aerosols of measurable protein which is quantifiable and
safe.
- 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
- 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.
- 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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