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| FAQ - Answer 1
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| How do AquaFlux TEWL measurements
compare with conventional open-chamber measurements? |
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The
AquaFlux out-performs all its competitors in terms of accuracy, sensitivity,
repeatability, reproducibility and versatility.
Below, we present data on three aspects, namely
(A) how do they correlate, (B) how do the numbers compare and
(C) where's the difference.
(A) How do they correlate?
AquaFlux measurements correlate well with open-chamber measurements.
This has been established in a number of studies on different
skin sites and many volunteers. The example shown below is from
a study performed by independent scientists experienced in the
use of open-chamber TEWL instruments.
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(B) How do the numbers compare?
Although the measurements correlate well, the the numbers generally
differ. This is due to calibration differences, with no agreement
among manufacturers about best practice. The calibration disagreement
in the above case is large, approximately a factor of 2.
Such disagreements can be resolved by the traceable droplet
calibration method developed in collaboration with the UK National
Physical Laboratory.
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| (C) Where's
the difference?
The main difference between AquaFlux and open-chamber methods
is in the quality of the measurements. This is illustrated below,
where an AquaFlux signal is compared with those from two
open-chamber instruments under well-controlled
laboratory conditions using procedures recommended by the manufacturer,
but without a shielding box. Ambient
air movements do not affect closed chamber AquaFlux signals,
but cause additional disturbance to open-chamber signals.
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| Signal fluctuations cause
scatter in TEWL measurements. One comparative test, for example,
found AquaFlux TEWL repeatability to be more than ten times
better (CV=1.4%) than comparable Evaporimeter
repeatability (CV=16%). See IFSCC
Magazine, 5(4), 297-301, 2002 for details.
How this translates into practice is illustrated in the figure
below, where two skin sites of the same volunteer were repeatedly
tested in alternation.
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| The somewhat higher scatter in the
measurements on the palm of the hand may be due to skin heterogeneity
and imprecise probe placement. Note that no air-conditioning or
other ambient environment controls are needed for such measurements.
The above data were obtained at home, watching TV. |
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