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FAQ -
Answer 8
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| Do the TEWL Guidelines (Contact Dermatitis,
EEMCO) apply to AquaFlux TEWL measurements ? |
The quick answer is yes and no. Yes, much of what they recommend is valid
for all measurement methods. No, they were written
for open-chamber instruments and the AquaFlux is different. If you want
the long answer, read on.
The Guidelines in question [1, 2] pre-date the invention of the AquaFlux.
Guidelines [1] consider only the Evaporimeter Model EP1 manufactured
by Servomed, whereas Guidelines [2] include newer open-chamber
instruments.
Both publications discuss (a) person-linked variables, (b) environmental
variables and (c) instrumental variables in some depth before presenting
their recommendations for best practice. Most of the considerations
of sections (a) and (b) are valid for all methods of measurement. The
exceptions are section (a) of [2], where the discussion
of skin surface temperature includes consideration of how this may
affect the measurement probe, and section (b) of both reports, which
includes discussion of air circulation and how this may cause
fluctuations in (open-chamber) measurements. Neither of these are concerns
for the AquaFlux. Section (c) and elsewhere is instrument-specific
and not applicable to the AquaFlux.
The table below presents a side-by side comparison of the recommendations
presented at the end of each publication with what we recommend for
the AquaFlux.
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Guideline Citations |
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Ambient Conditions |
If climate room facilities are available,
the ambient room temperature should be regulated to 20-22°C
and the relative humidity to 40% [1].
Usually it is suggested to keep the temperature between 20 and 22±1°C
and the relative humidity lower than 60% [2]. |
These recommendations are valid for all TEWL
measurement methods. They define the conditions necessary for skin
acclimatisation, to avoid sweat gland activity and skin surface
moisture. You cannot take the bio out of bioengineering. |
Shielding Box |
Perform all TEWL measurements within a
large "open-top" box whenever possible [1].
Measurements should be carried out in a room with limited air circulation. A
shielding box with an open top can be used if doubt exists whether undesirable
air turbulence is present or not [2]. |
Ambient air movements and turbulence have no effect on AquaFlux
measurements. |
Post-measurement
Recovery |
Avoid using the "offsett" button in between measurements
for zeroing and allow it to "zero" on its own, before
the next measurement is made. (2-4 minutes post-measurement) [1].
An
equilibrium time should be taken into consideration before the
next measurement is started. The process can be accelerated by
moving the probe [2]. |
No recovery time is necessary before starting the next measurement,
because of the controlled microclimate. You can hop from site to
site. |
Holding
the Probe |
Do not hold the probe directly by hand. The
probe should be handled with an insulating glove, or the calibration
rubber stopper supplied with the equipment, or a burette clamp
[1].
The measuring probe itself should not be touched before and
during measurements and can be handled with the electrical wire,
a coating or by wearing gloves [2]. |
There are no measurable effects from hand heat
while holding the AquaFlux probe. |
Contact Pressure |
The contact pressure of the probe onto the skin should be kept
low and constant [1].
... with a constant but light pressure. Measurements
within one experiment should preferably be performed by the same
operator [2]. |
No measurable contact pressure effect has been found. This appears
to be an open-chamber design deficiency rather than a skin property. |
Surface Orientation |
The measuring surface should be placed in a horizontal plane,
and the probe applied parallel to this surface [1].
The measuring surface should be placed in a horizontal plane
and the probe should be applied perpendicularly to this surface
[2]. |
You can measure with any surface orientation.
You need to hold the probe correctly to limit sensitivity
changes with probe angle to ±1%. |
References
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| [1] |
J Pinnagoda, RA Tupker, J
Agner and J Serup. Guidelines for transepidermal
water loss (TEWL) measurement. A Report from the Standardization
Group of the European Society of Contact Dermatitis. Contact Dermatitis, 22,
164-78, 1990.
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| [2] |
V Rogiers and the EEMCO Group. EEMCO
Guidance for the Assessment of Transepidermal Water Loss in Cosmetic
Sciences. Skin Pharmacol Appl Skin Physiol, 14,
117-28, 2001. |
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