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Treatment of chronic wounds by means of electric and electromagnetic fields

Part 2 Value of FES parameters for pressure sore treatment

  • Rehabilitation Engineering
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Abstract

Subjects with spinal cord injury are often distressed by pressure sores, which usually appear after prolonged pressure (wheelchair, bed) across the soft tissue which has already lost sensibility and has diminished microcirculation. The healing ability and its dynamics depend on the state of the subject's overall health. Consequently, evaluation of a particular treatment requires careful consideration of as many as possible of the parameters relevant to healing and an adequate criterion for assessing the state of the pressure sore. Bearing in mind these two circumstances, the results of a multicentre clinical study are analysed. The aim of the study was to test two hypotheses: first that healing is faster when sores are also treated by electric currents (ECs) (in addition to conventional treatment); and secondly that there exist differences in the efficiency of the treatment if direct or low-frequency pulsed currents (FES parameters) are applied. The data analysed show that pressure sores are likely to heal twice as fast when treated with low-frequency pulsed currents. EC seems to improve the healing rate in cases where the natural healing mechanisms of the body are not sufficient (chronic wounds, older subjects).

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Abbreviations

θ:

healing rate (in per cent per day)

τ:

healing time constant = 100/θ (in days)

S 0 :

initial wound area—area of the wound surface at the beginning of the treatment

\(\hat S\) :

estimated value of the area of the wound surface

\(\hat S_l \) :

when the time course of the surface area is linearly fitted

\(\hat S_e \) :

when exponentially fitted

EC:

electric current

AC:

low-frequency pulsed currents

AC group:

wounds treated with AC currents

DC:

low-density direct currents

DC group:

wounds treated with DC currents

CO group:

wounds treated by conventional medical methods

wound case:

wound treated in a particular time interval (at least four weeks) with the same treatment. The same wound may be included in at most two wound cases; the first wound case would be CO treatment for four weeks, and the second wound case AC or DC treatment either up to wound closure or for at least four weeks

pressure sore:

wound of the soft tissue resulting from increased duration of pressure on a certain part of the body in a person with decreased microcirculation; decubitus ulcer is also a notation used

area of the:

the area of cavity on the surface of the

wound surface:

body due to damage to and decomposition of the tissue; also wound area

SCI:

spinal cord injury

DurDis:

duration of disability of a patient with a particular wound (in months) up to the moment of initiation of a particular treatment (DC, AC or CO)

Age:

patient's age (in years)

WoDur:

wound duration up to the beginning of a certain treatment

InArea:

wound area at the beginning of the treatment (alsoS o in cm2)

InD:

value of the wound depth at the beginning of the treatment

t :

separate variance estimate in the two-samplet-test, defined as:

$$t = \frac{{\bar x - \bar y}}{{\sqrt {S_x^2 /N_x + S_y^2 /N_y } }}$$

where\(\bar x\) and\(\bar y\) are two population means,S 2 x andS 2 y their variances andN x andN y their sizes

F :

the ratio of the larger sample variance to the smaller

p :

the probability that two population means are equal; ifp≤0·05 (significance level) then the hypothesis that two population means are equal can be rejected

ρ:

correlation coefficient between two parameters (x andy), defined as:

$$\rho = \frac{{\sum {(x_i - \bar x)(y_i - \bar y)} }}{{(N - 1)\sqrt {\sum (x_i - \bar x)^2 } \sqrt {\sum (y_i - \bar y)^2 } }}$$
P :

the probability that a correlation coefficient is obtained when there is no linear association in the population represented by two parameters, based on the expression:

$$t = \rho \sqrt {(N - 1)/(1 - \rho ^2 )} $$

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Authors and Affiliations

  1. Faculty of Electrical & Computer Engineering, University of Ljubljana, Tržaška 25, 61000, Ljubljana, Slovenia

    A. Stefanovska & L. Vodovnik

  2. University Rehabilitation Institute Soča, University of Ljubljana, Tržaška 25, 61000, Ljubljana, Slovenia

    H. Benko & R. Turk

Authors
  1. A. Stefanovska
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  2. L. Vodovnik
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  3. H. Benko
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  4. R. Turk
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Stefanovska, A., Vodovnik, L., Benko, H. et al. Treatment of chronic wounds by means of electric and electromagnetic fields. Med. Biol. Eng. Comput. 31, 213–220 (1993). https://doi.org/10.1007/BF02458039

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