Pergamon
PI I: S0003-4878(98)00063-5
r
Ann. occup. Hyg., Vol. 42. No. 8. pp. 541-547. 1998
E 1998 British Occupational Hygiene Society
Published by Elsevier Science Ltd. All rights reserved
Printed in Great Britain.
0003-4878/98 SI9.00+0.00
A New Whole-body Exposure Chamber for Human Skin
and Lung Challenge Experiments^the Generation of
Wheat Flour Aerosols^
C. LIDEN*t^l, L. LUNDGREN*, L. SKAREt, G. LIDENJ, G. TORNLING§
and S. KRANTZJ
^Department of Occupational and Environmental Dermatology, Karolinska Hospital! SE-\ 71 76
]Stockholm, Sweden^ Department of Occupational Health (Dermatology Division), National Institute
for Working Life, SE 17] 84 Solna, Sweden; %Department of Work Organisation and Technology,
National Institute for Working Life, Solna, Sweden; ^Department of Respiratory Medicine. Karolinska
Hospital. SE-\7] 76 Stockholm. Sweden
I A new whole-body exposure chamber for human skin and lung challenge offers possibilities for
experimental exposure challenges carried out in clinical practice, for exposure of patients, in
research and for investigations of the effects of exposure on the skin and in the respiratory tract.
The chamber system can be used for both aerosols and gases. Dynamically controlled, the chamber
is relatively easy to operate and to clean. Air exchange rates can be varied between 6-12/h. Initial
studies with wheat Hour have been carried out. The homogeneity and stability of the wheat flour
aerosol concentration (the spatial and the temporal variation) inside the chamber can be kept at
acceptable levels. \ < 1998 British Occupational Hygiene Society. Published by Elsevier Science
Ltd.
"^
Keywords: aerosol generation: chamber design; provocation chamber; exposure chamber; lung; skin: wheat
flour: whole-bodv
INTRODUCTION
Airborne contact allergens, irritants and Type-I allergens may cause contact dermatitis, urticaria, asthma
and rhinitis. The clinical significance of exposure is
however often difficult to evaluate. Exposure chambers are valuable in studying respiratory symptoms
since they can provide a controlled environment and
can maintain conditions for measuring the level of
allergens and irritants inducing symptoms in sensitive
subjects. So far there is very limited experience of
application of the technique in dermatology.
A few whole-body exposure chambers or exposure
rooms for humans are described in the literature
(Seiner, 1996; Butcher, 1979: Hackney el ai, 1975;
Ranborg el at., 1996). One often cited is the Vienna
Challenge Chamber (Horak and Jager, 1987; Horak
el ai, 1996). This large chamber system has been successfully used in challenge research with many conReceived 29 April 1998; in final form 9 July 1998.
"' Author to whom correspondence should be addressed. Tel:
0046 8 517 736 17; Fax: 0046 8 34 44 45; E-mail:
Qidenfo yderm.ks.siTJ
Received 29 April 1998: in final form 9 July 1998.
§41
ventional in-door allergens. Some chambers are constructed for studies of the effect on the respiratory
system of air, humidity, temperature and irritants.
Some are used in research concerning office machines
and the sick building syndrome (SBS) (Wolkoff e/ ai,
1992; Horak el ai, 1994). Smaller exposure chamber
systems for animals are more frequently described
(Phalen, 1984; Karg el ai, 1992). Yao and Krueger
(1993) have reported exposure chamber systems for
monitoring aerosol measuring equipments.
Most chambers for human exposure studies are
constructed for gases only. One whole-body chamber
recently described (Sestrand el ai, 1997) was built to
perform studies principally for gases but also for some
paniculate matter. Another chamber constructed for
both gas and particle exposure is used for research
and clinical examination of allergic respiratory and
dermatological effects (Professor H. Nordman, Finnish Institute of Occupational Health, Helsinki).
Methods used for exposure with allergens often present problems of reproducibility. They might also lack
in realism in different respects and some do not allow
simultaneous challenge of the whole human body, i.e.
skin and respiratory tract. Neither can they give the
542
C. Liden et al
means of quantitative and dynamic provocation
required for an optimal exposure challenge.
The aim of the work reported here was to construct
a whole-body exposure chamber for humans which
can be used in research for developing new techniques
of experimental and controlled exposure of the skin
and/or the respiratory tract. The system should be
usable for particles and gases, and easily switched
from aerosol to gas exposure, separately or simultaneously with aerosols. The chamber is to be used
for contact allergens, IgE-mediated allergens and irritants for challenge in allergic subjects and in controls.
Initial studies with wheat flour have been carried
out. Wheat flour is an occupational allergen (Tikkaintnetal., 1996; Houba, 1996) known to cause baker's
asthma and also contact dermatitis and urticaria.
Aerosols of extremely large particles like wheat flour,
have previously proved difficult to generate and to
keep at a homogeneous and stable concentration in
exposure chambers (Cheng el al., 1989; Cloutier and
Malo, 1992).
DESIGN
General
Based on expert knowledge from aerosol physicists,
medical and ventilation experts, the exposure chamber
system was designed according to the following criteria:
—It should be built as a closed chamber system so
that contaminated air could pass neither into the
chamber nor into the connecting room.
—It should have a dynamic air-through system, for
continuous air flow and the introduction of agents.
—The air-delivery system should be adjustable and
controllable.
—Provocation with both aerosols and/or gases should
be possible.
—The whole system should be easy to handle and to
clean.
—The construction materials should be inert to water
and to chemical substances.
—The materials should not contain or release allergenic, irritant or other toxic substances.
—It should be possible to dismantle the chamber, to
move and to reassemble it.
The system was designed and built so as to keep the
variability in spatial (location variable) and temporal
(time variable) distribution of the experimental agent
as low as possible. Important factors influencing this
homogeneity in a chamber are the design of the actual
chamber, the mixing of aerosol- or vapour-laden air
into the main clean air supply and the particle size
distribution of aerosols. Additional factors linked to
the air-moving equipment and the air delivery system
can also influence the concentration homogeneity.
and the floor are made of stainless steel while the main
part of the front wall is glass. The purpose of glass is
continuous observation of the subject and also to
reduce discomfort and possible claustrophobia. Stainless steel is sufficiently inert for most experimental
atmospheres, it is durable and does not build up localised electric surface charges. The section strips are of
aluminium and all pipes are of steel or plastic. The
sealings, gaskets, tubes and filters are all rubber-free
and formaldehyde-free.
The exposure chamber is designed for the exposure
of one subject at a time. Floor size is 1.8 x 1.5 m
and the height is 2.1m (volume 5.7 m3). The room
is furnished with an aluminium chair only. The
actual exposure room is connected to a sluice
(1.8 x 0.9 x 2.1 m). This sluice is equipped with a hand
shower and a draining gutter. Hot and cold water are
available mainly for cleaning the inside of the chamber
between experiments. Because of the interior design
and materials, the chamber is very easy to clean.
Ports (inlets/outlets) on the front wall are used for
connecting different equipment placed outside the
chamber, such as air sampling devices, spirometry and
respiratory air supply. This makes it possible for the
subject to inhale fresh air while skin exclusively is
exposed. Dynamic spirometry may be performed during an experiment by connecting spirometry tubes to
an outlet/inlet and placing the spirometer outside the
chamber.
A ir delivery system
A schematic figure of the air delivery system is
shown in Fig. 3. Room air is supplied to the exposure
chamber through microfilters (Camfil Airopac CPM60 and CPM-95) by a modified centrifugal fan
(Exhausto BESF 146-4-3). The air flows from the
chamber into the sluice through an exhaust grille
located in the connecting wall. The polluted exhaust
air from the sluice is cleaned through a microfilter
(Camfil Airopac CPM-60) vented outdoors via a separate centrifugal fan (Exhausto VVR). The system is
sealed (a closed chamber system) and contamination
by room air or from other sources into the exposure
chamber is avoided by maintaining a small static overpressure in the chamber compared to the sluice
(~ 2 Pa). Leakage from the sluice is prevented by
keeping a small static under-pressure in the sluice
(— 1 Pa) compared to the outer room.
A forced exhaust capability is also installed in the
air delivery system to be used whenever rapid evacuation of dangerous and hazardous agents is needed.
In a very short time contaminated air in the whole
chamber system can safely be evacuated.
The controlled pressurised atmosphere with airvolume flow from the main air supply in the range of
500-1100 litre/min and from the secondary air supply
from the aerosol generator of 60 litre/min corresponds
to air exchange rates of 6-12/h in the chamber. Since
Exposure chamber
The exposure chamber was designed as a whole- it is possible to exchange different parts of the system,
body chamber (Figures 1 and 2). Three walls, the roof for example a more powerful centrifugal fan. the
A new whole-body exposure chamber for human skin and lung challenge experiments
543
if
Fig.
and hands is directly exposed to the air. "Dosimeters' for measuring deposition on the skin are placed on forehead and
shoulders. (Photography by Bo Nasstrom and Lars-Erik Bystrom).
characteristics of the system can be varied depending
on the requirement for each type of challenge.
The air delivery system is fairly easy to manage and
to keep clean. The filters and the pipes are easy to
dismantle, exchange and clean.
Aerosol generation and uerosol characterisation
The exposure chamber system can be run with
different aerosol generators. In the present study an
RBG 1000 (Palas GmbH) was used. This generator is
preferable when working with free-flowing powders
such as wheat flour that cannot easily be packed. In
the generator, dry powder from a reservoir located
below a rotating brush is transported upwards at a
given speed into the brush. When the brush has turned
180' the powder is blown off by a high-velocity air
stream (compressed air in the range of l-5m 3 /h).
Different sizes of powder reservoir are available for
mounting different quantities of material in the generator.
A Wright dust feeder as described by Wright (1950)
was tested. This can be packed and loaded with more
material than the RBG 1000. The principle of the
feeder is that small fractions of material are scraped
off from a rotating cake consisting of the material,
packed under high pressure (tons). The fractions are
picked up by a compressed-air stream and then
directed into the main air supply. It was, however,
shown that the distribution of the particle size of the
wheat flour was altered by the Wright dust feeder,
possibly due to the packing and scraping.
The aerosol leaving the generator is transported
through a tube containing a krypton 85 source to
neutralise the electrical charges on the particles. This
aerosol-laden air is turbulently mixed with the filtered
clean air in the duct and dispersed downward into the
chamber. A cone pointing into the duct forces the air
to enter the chamber with a radial velocity component
thereby increasing the mixing in the chamber. This
turbulent flow creates a more uniform spatial and
time variable distribution of aerosols in the chamber.
However, since wheat flour was used in our studies,
low spatial variation was very hard to achieve. This
variation was estimated by simultaneously sampling
with filters at different locations inside the chamber.
The aerosol concentration and the spatial dis-
544
C. Liden el al
Exhaust air
Secondary air
supply via
aerosol generator
Inlets/outlets for instruments,
| respiatory air, spirometer
Fig. 2. The chamber with sluice. Materials: glass, stainless steel and aluminium Floor: 1.8 x 1.5 m + 1.8 x 0.9 m, height 2.1m.
(by Bo Nasstrom).
Turbulent
Mixing
•
riuer
•
Fan
•
Neutralizer
Filter
••
Fan
Aerosol
Generator
•
Pressurized
Air
•
•
Release to
outdoor air
Room
Air
Fig. 3. Schematic figure of the air-delivery system, (by Goran
Liden and Lars-Erik Bystrom).
tribution were determined by conventional air sampling on 37 mm membrane filters, both with total dust
holders and respirable dust cyclones (Casella SIMPEDS). Respirable dust is defined as those particles
that can penetrate into the gas-exchange regions
(smaller parts) of the human lung. The Casella cyclone
approximately follows the Johannesburg convention
(Second Pneumoconiosis Conference, Johannesburg
1959). The membrane filters were run at 2 and
l.9l/min respectively. During aerosolization, dust
concentration was also measured and recorded on
paper by a direct reading instrument (Casella
AMS950) based on infra-red light scattering. The
Casella AMS950 instrument was frequently calibrated
against the total dust membrane filter samplers, giving
information on the actual aerosol concentration
directly during a provocation. With this instrument a
good estimate of the time variable distribution in the
chamber was achieved.
For determination of the aerodynamic particle size
distribution, cascade impactors PIDS (Gibson el al.,
1987) were used and run at 21/min. The impactor
plates were coated with 10% apiezone in toluene.
The membrane filters and the impactor plates were
weighed before and after sampling in a controlled
weighing room.
Safely and ethics
The chamber was designed to be safe for subjects
participating in experiments. It was made of nonalleraenic and inert materials, and easv to clean to
A new whole-body exposure chamber for human skin and lung challenge experiments
avoid contamination by substances used in previous
experiments. Exposure levels will continuously be followed by the use of direct reading instruments. Experiments will be carried out at or below levels found in
work places or at the corresponding threshold limit
value. In the case of experiments with healthy subjects
this would be regarded safe. In the case of subjects
and patients allergic to substances used, it will be
extremely important to take great care to avoid severe
allergic reactions. The chamber is situated at the
Department of Respiratory Medicine, with access to
intensive care in case of emergency. Provocation
experiments will be subjected to review for approval
by the Ethical Committee.
PERFORMANCE
Some characteristics of the aerosol concentration in the
chamber
Airborne wheat flour concentration around
5 mg/m3 (a concentration not uncommon in bakeries
as reported by Tikkainen et al. (1996), Houba (1996),
Lillienberg and Brisman (1994)) was easily achieved
with the RBG 1000. The duration of such a concentration is approximately two hours. Higher concentrations can be obtained (12mg/m 3 during one
hour has been tested). The duration of such a high
exposure is however limited since the aerosol generator runs out of flour.
The respirable fraction determined with the Casella
cyclones is about 6-12% of the total dust concentration which corresponds fairly well with what
might be expected in bakeries (Lillienberg and Brisman 1994).
Wheat flour aerosols on a Nuclepore membrane
filter (pore size 0.4 /<m) sampled in the exposure chamber are shown in Fig. 4, a SEM-picture (Scanning
Electron Microscopy) at 800X magnification. The
spherical particles are starch, the others are protein
particles and/or clusters with starch and proteins.
Uniformitv of dust concentrations
All experiments and calculations of the concentration uniformity were carried out with wheat
flour, an extremely coarse aerosol that might be
difficult to generate as well as to keep at a stable level.
The temporal variation (time variable) in the chamber
was calculated from the recorded chart of the direct
reading instrument. This was done with data obtained
on three separate occasions with subjects in the chamber. For a dust concentration estimated every 5th
minute during one hour of exposure, the coefficient
of variation (c.v.) for an average dust concentration
between 4.2-5.1 mg/m3 was in the range of 7-11 %.
The spatial (location variable) variation was tested
with and without a human subject in the chamber.
These tests were performed with up to 5 total dust
holders placed around a subject and around an empty
chair respectively—from the waist up to the breathing
zone or around the upper part of the chair—and were
545
run at concentration levels around 5 mg/m3 of wheat
flour for 1 hour. A total space of approx. 100 dm3 was
thus investigated. These tests, measured on different
days, were repeated twice with subjects and up to 8
times with no subject giving a pooled spatial variation
(the coefficient of variation (c.v.)) of 15% in the interval 7-20%. No difference in spatial variation with or
without subject in the chamber could be observed.
The temperature rise with a subject inside the chamber
for one hour was ~ 1.3CC. At a wider space around
a subject (3 additional total dust holders placed at
different locations) the spatial variation was of the
same order, indicating uniform distribution in the
main part of the chamber.
Aerosol size distribution
Figure 5 plots the mass aerodynamic particle size
distribution for the wheat flour aerosol in the chamber, as measured with the PIDS impactor. As a comparison, the particle size distribution in the breathing
zone of trough mixers in a Swedish automated bakery
is also shown (Liden et al., to be submitted). Both
curves show two particle modes, for finer particles at
approx. 6-10//m, and for coarser particles at approx.
50 /(in. The finer particle mode consists mostly of free
proteins and small starch particles, whereas the coarse
mode mainly consists of clusters of starch and protein.
Figure 5 shows that, compared to the bakery, the
fraction of small particles is larger in the chamber,
and that their size is somewhat smaller. This means
that subjects in the chamber will be exposed to a
slightly higher amount of flour dust particles in the
respiratory tract beyond the larynx compared to in
the bakery at the same given total dust concentration.
For lung challenge studies this might not necessarily
be a disadvantage since the respirable and thus potentially harmful fraction is just slightly enhanced. As
long as the actual distribution is known, adequate
lung experiments might easily be performed. The effect
of particle size for skin deposition and uptake has
however never been studied and is not known.
Other studies
During the work with wheat flour exposure, initial
experiments for the development of techniques aiming
at measuring the deposition on human skin and on
surfaces were performed. One technique involves
patch sampling on different parts of the body, with
small pieces of thin glass (microscopy cover glass)
covered with different types of adhesive tape. These
patches can be gravimetrically determined with high
accuracy before and after exposure and are easily
investigated with light microscopy and image analysis
(polarised, epi-fluorescence and phase contrast techniques have been used). With fluorescence microscopy
it is possible to selectively determine different components in wheat flour such as starch, total proteins,
lipids and some enzymes. We have also used tape
stripping followed by fluorescence microscopy for skin
deposition measurements. These and other techniques
C. Liden el al
546
Fig. 4. Scanning Electron Microscope (SEM) picture of airborne wheat flour in the chamber. The spherical particles are
starch, the others are protein particles and/or clusters with starch and proteins.
— Test Chamber
- - Trough mixing
i
0,7
1,0,6|
0,5-
<
0,*
0,*
0,2
0,1
1
10
100
Aerodynamic diameter (uml
Fig. 5. The aerosol size distribution of wheat flour in the chamber and in a bakery (trough mixing).
will be further developed and evaluated in future
experiments and with different aerosols. These studies
will be presented separately.
SUMMARY
This whole-body exposure chamber system will present unique possibilities for experimental exposure
challenges that can be carried out in clinical practice,
for exposure of patients, in research and for investigations of the effects of exposure on the skin and the
respiratory tract. The system will present opportunities for more accurate cause-relationship judgements in the investigation of patients than are currently possible. Occupational and environmental
allergens and irritants will be used.
The system is designed and built to provide the
properties required for a controlled environment,
including safety. It offers challenge conditions for airborne allergens and irritants affecting skin and/or respiratory tract, and it can be run with both particles
and gases separately or together. The dynamically
A new whole-body exposure chamber for human skin and lung challenge experiments
controlled exposure chamber is relatively easy to operate and the stability of the temporal and spatial wheat
aerosol concentration levels inside the chamber is
acceptable.
Acknowledgements—This work was supported by the Swedish Council for Work Life Research (RALF) and by the
Swedish Asthma and Allergy Association. The authors
would like to thank Sten Lundstrom for his valuable technical assistance.
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