Skin electrical properties and physical aspects of hydration of keratinized tissues

118 Pages·2010·1.71 MB·English

Skin electrical properties and physical
aspects of hydration of keratinized
tissues
by
Gorm Krogh Johnsen
Thesis submitted for the degree of
Philosophiae Doctor
Department of Physics
University of Oslo
June 2010
© Gorm Krogh Johnsen, 2010

Series of dissertations submitted to the
Faculty of Mathematics and Natural Sciences, University of Oslo
No. 1015

ISSN 1501-7710

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Acknowledgements
I am deeply indebted to Ørjan Martinsen and Sverre Grimnes for being
superb supervisors over the last four years. Your insight in the field of
bioimpedance as well as your patience has been invaluable for me all the
way since I was fumbling around way off thefrontier ofresearch. Also, your
friendly attitude and fine, but still a bit dry wit has been very much appre-
ciated, as well as all the laughs in your office.
I am also grateful to Lars Norlen for a good and interesting collabora-
tionregardingaspectswithinskinresearch. CarstenLu¨tkendeserves special
thanksforintroducing metothetreasurousseasofmemristors. Iwould like
to thank Christian Tronstad for fully jumping onto the last project in my
thesis, involving very hard and much work over a long period with really
tight time limits.
I have also had thepleasure ofcollaboratingwith Havard Kalvøy, Anne-
Berit Haugsnes, and Per Høyum, as well as Bernt Nordbotten concerning
small and even smaller problems on a daily basis. Jan Gorgol at the SMS
Ltd (London) has been very helpful concerning the use and maintenance of
the DVS instrument. All conference-trips with the friendly gang of Oslo
Bioimpedance Group have been inspiring, but more importantly, very nice.
Øyvind Grøn has been extremely friendly and easy to work with con-
cerning my teaching duties over the last three years. Your pedagogical and
inspiringexplanationstosmallsubtletieswithinGeneralRelativityhavebeen
indispensableinmywork. Iamalsogratefultothealwayspositivelibrarians
attheDepartmentofPhysics,andfortheireffortindiggingupoldliterature.
Finally,Iwouldliketothankmyfamilyforallsupport,andinparticular
Josefineforbeingthebestever,neverlettingmeburymyselfinthemysteries
of bioimpedance.
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List of abbreviations
SC - stratum corneum
RH - relative humidity
EDR - electrodermal response
EP - electrode polarization
DC - direct current
AC - alternating current
LF - low frequency
HF - high frequency
TEWL - trans-epidermal water-loss
CPE - constant phase element
DVS - dynamic vapor sorption
SSCD - skin surface conductance density
TS - test subject
IQR - interquartile range
EEA - effective electrode area
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Preface
The first four chapters in this thesis are written with the purpose of intro-
ducing the reader to the field of bioimpedance, skin sorption properties as
wellasthethrillingmemristorcircuitelementthatallhavebeenkeytopicsin
my research. The topics covered are naturally biased, as well as limited, by
my own overview of these fields, but nevertheless the introduction is meant
toserve asguideand motivationto thepapersthatarethefinal outcomeof
my research during the last years.
The anatomy and physiology of the human skin are treated in chapter
1. Chapter2introducesskin electrical properties, whereas itscorresponding
waterholdingcapacitiesarebrieflydiscussedinchapter3. Memristortheory,
suitableforbiologicalsystems,isintroducedinchapter4. Finally,inchapter
5 I summarize the main findings in my thesis, sharing also some thoughts
about natural follow-up studies.
Electrical bioimpedance is a field of research that has evolved mainly in
the last 30 years and this research has provided a detailed knowledge about
the passive (i.e. no internal current source) electrical properties of human
as well as other tissues. One possible application that has been quite thor-
oughlystudied,istheabilityofgivingadescriptionofthehydrationstateof
thestratumcorneum(SC),theuppermostpartofthehumanskin,bymeans
of electrical measurements. As the general hydration state of the SC is con-
nected to its passive electrical properties as well as to the overall function
of the SC, serving as a protective shield against the environments, the role
of water in the skin has been studied with interest within dermatology as
well as by researchers concerned with bioimpedance and bioelectrical phe-
nomena. In general, information gathered from impedance measurements is
afingerprintofthetissuepropertiesaswellasoftissuealterations,andsoas
an example skin hydration can be linked to the physical parameters of skin
barrierfunctionsoralterationscanbelinkedtospecificskinrelateddiseases.
Thus, being able to estimate the actual content of water within the SC
canbeexpected tobeastrongclinicaltool,enablingbetterdiagnostics, and
a good precision of the estimates is thus desirable. As one of the foremost
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functionsoftheSCistoprovideadiffusionbarriertowardstheenvironments,
its water hydration characteristics have been and will be important in a
structure function understanding of the SC. This argument also applies for
keratinized tissue, that is a more general grouping of tissue in the human
integument such as hair, nail and SC.
Modeling the human SC as well as the rest of the skin is important in
order toactually understand the underlying physics and hence possibly also
enable improved diagnostics in some applications. It is desirable that the
modeling, often based on amore orless intricate combination of elementary
circuit elements is not only precise in its description (i.e. mimicking the
observations to a good precisison), but also conceptually correct, giving an
improved understanding of the physical phenomena at their fundamental
level. This is where the memristor comes in.
Itisimportanttokeepinmindthatelectricalmeasurementsonorwithin
the human body involve electrodes, i.e. the site where charge carriers shift
from electrons to ions, and electrodes will in general influence the signals
that are measured. Hence, electrodes should always be chosen carefully in
order to bemost suitable for the intended use.
Six papers are presented in this thesis and are referred to by Roman
numbers I-VI throughout the text. These papers represent, at least in part,
answers to some of the key questions that during the last four years have
served as a motivation for my daily work. The two first papers describe
methods for estimating the stratum corneum water content, both based on
electrical measurements (Paper I)aswell asonskin water evaporationmea-
surements (Paper II) and are steps towards an objective measure of the hy-
drationstateofthestratumcorneum. Thesearemethodsthat,ifsufficiently
precise,wouldbeusefulinevaluatingtheprotectivepropertiesofthestratum
corneum as well as within understanding of skin diseases. Paper III and IV
deal with the water sorption properties, intimately related to skin electrical
properties, of keratinized tissues. In Paper V the memristor, which is the
fourth and final passive circuit element, complementing resistors, capacitors
andcoils,isintroducedtotheworldofbioimpedance,andhumansweatduct
conductivity in particular. The memristor shows promising abilities in ex-
plaining some puzzling non-linear phenomena in circuit theory, and hence
also in bioimpedance measurements. Finally, Paper VI deals with the same
sweat ducts, but nowwith focusonhowdifferent typesofelectrodes will in-
fluence the final signals that are recorded, and we will see that an electrode
is not necessarily just an electrode.
List of papers
Paper I: GK. Johnsen, ØG. Martinsen, and S. Grimnes,
Estimationof invivo watercontentof the stratum corneumfrom
electrical measurements,
Open Biomed Eng J, 3, 8-12,2009.
Paper II: GK. Johnsen, AB. Haugsnes, ØG. Martinsen, and S. Grimnes,
A new approach for an estimation of the equilibrium stratum
corneum water content,
Skin Res Technol, 16, 142-145,2010.
Paper III: GK. Johnsen, L. Norlen, ØG. Martinsen, and S. Grimnes,
Sorption properties of the human stratum corneum,
Skin Pharmacol Physiol (submitted), 2010.
Paper IV: GK. Johnsen, ØG. Martinsen, and S. Grimnes,
Sorption studies of human keratinized tissues,
J Phys Conf Ser, 224, 012094,2010.
Paper V: GK. Johnsen, CA. Lu¨tken, ØG. Martinsen, and S. Grimnes,
A memristive model of electro-osmosis in skin,
J Phys D (submitted), 2010.
Paper VI: C. Tronstad, GK. Johnsen, S. Grimnes, and ØG. Martinsen,
A study on electrode gels for skin conductance measurements,
Physiol Meas, 31, 1395-1410,2010.
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