Electrical Conductivity of Skin Compared to Skin Perfusion Recordings

Introduction

The skin is the body’s largest organ and serves as a protective cover between the body and the environments. The anatomy of skin is illustrated in Sobotta & Becher (1976) and anatomy and skin functions are described in detail by Archer (2000).

The purpose of the present work is to demonstrate recordings of the electrical impedance between sets of electrodes positioned on specified sites of human skin and compare these results to skin perfusion data retrieved by heat transfer measurements at the same sites.

Measurement of the impedance of living tissue is generally done using a set of surface electrodes placed on the skin and connected to auxiliary circuits for the recording of the voltage between the electrodes and the corresponding current passing from one electrode to the other. The ratio between voltage and current is defined as the impedance . The type of electrodes used, the frequency and amplitude of the applied electrical current and the extent, anatomy and physiology of the tissue in question have all together influence on .

Birgersson (2012) measured the Impedance of human skin and developed a mathematical model to ascertain the validity of skin properties found in the literature. Wilson and Spence (1988) accounts for the anatomical and physiological properties of the skin and state a number of skin parameters with relation to heat transfer of skin. Cohen (1977) presents a review of existing data concerning heat conduction and the specific heat of excised and in vivo human skin. Johnsen (2010) deals extensively with electrical properties of skin and with the determination of water in keratinized skin tissues.

The outer layer of the skin is the “Epidermis”, which has a protective corneous layer called Stratum Corneum with very low electrical conductivity. Under the epidermis is a layer called the Dermis or Corium, containing the protein Collagen constituting connective tissue fibres. Corium also contains capillary blood- and lymph vessels, sensory organs, sweat glands and nerves providing essential information to the rest of the body which in turn regulates relevant functions of the skin. An example of this “Feed Back” function is the electrodermal activity (EDA) which affects the electrical conductivity of the skin (Critchley, 2002; Johnsen, 2010). Under the Dermis is a layer of subcutaneous fatcells (“Subcutis”) having low electrical conductivity. Impedance recordings can be influenced by underlying tissues such as bones, muscles and greater blood- and lymph vessels.

High electrical conductivity (low impedance) between electrodes and underlying skin and low inherent electrical noise level are important provisions for the recording of electrical signals such as ECG and EEG as described by Smith (1992); Assambo, Baba, Dozio et al. (2007); and Spach, Barr, Havstad et al. (1966). Skin temperature studies have been performed with the aim of retrieving data relevant to Cardiac Out Put presented among others by Schey, Williams and Bucknall (2009).

The present work deals with recordings of the impedance between surface electrodes positioned on the skin covering the arched part of the human Musculus Tibialis Anterior and compare the results to skin perfusion data retrieved by means of heat transfer as described by Jarløv and Jensen (2014).