PERCUTANEOUS CONDUCTION OF ELECTRICAL SIGNALS: 
INTERFACE TECHNIQUES AND TISSUE REACTION 
AT ELECTRODE SITE 
J. T. Mortimer and P. H. Peckham* 
The use of hard wires for transmission of an electri- 
cal stimulus or for information retrieval has advan- 
tages over telemetry systems in many experimental 
procedures. The advantages of hard w^iring are: an 
electrical stimulus may be more precisely controlled, 
quantification of recorded signal is easier, there are 
fewer problems with electrical noise, and it is less 
expensive than most telemetry systems. A major prob- 
lem that one encounters with this technique is to main- 
tain an "infection-free" interface. The ability to main- 
tain an "infection-free" interface often determines the 
success of an experiment, particularly in long-term 
chronic experiments. The term "interface" is used here 
to designate any mechanical device which is implanted 
in the skin and through which lead wires pass. The 
purpose of the interface is to prevent infection and to 
anchor the lead wire. Subjective evidence indicates that 
the invasion of bacteria causing infection probably 
takes place via two mechanisms: 1) Bacteria may be 
carried into the body if the lead wire is permitted to 
slide freely in the wound through which it enters the 
skin; 2) Bacteria may also gain access through the 
small fissure between the skin and the wire or the inter- 
face. Several interfaces (using synthetic fibers and 
porous carbons) have been designed with these param- 
eters in mind. The implant results indicate that it is 
possible to maintain wires through the skin for pro- 
longed periods of time utilizing interface techniques 
which minimize slippage and fissure size. The Caldwell 
electrode has been found to be the most successful for 
both information retrieval and stimulation. The elec- 
trode has been implanted in muscles with good sta- 
bility and minimal tissue reaction in passive implants. 
Utilizing the electrode as a stimulating electrode, his- 
j tological studies indicate that the tissue reaction is not 
I statistically diff'erent from the passive implants for 
; stimulus parameters in the physiological range (100 
/jsec, 50 Hz, amplitude < 15 mA). 
INTRODUCTION** 
There are two basic ways to transfer electri- 
cal signals from one side of the skin to the other, 
telemetry and percutaneous wiring. To rate 
* Case Western Resei-ve University, Cleveland, Ohio. 
** This research was supported by the Social and Rehabilitation 
Services Grant Number 23-P-55207/5-02. 
categorically one technique over the other is in- 
appropriate since neither approach is without 
certain disadvantages. There are, however, cer- 
tain precautions one can take to minimize these 
disadvantages. With these precautions in mind, 
one can choose the method best suited for a 
particular experimental preparation. Briefly, 
a disadvantage of telemetry is that relative mo- 
tion between the receiver and transmitter an- 
tenna may introduce an undesirable error in 
the electrical signal. Also, calibration and main- 
tenance of calibration can be rather difficult. 
Other than the possibility of restricting the 
animal's movements, the primary problem with 
percutaneous signal transmission is mainte- 
nance of an "infection-free" interface. The 
following text is devoted to methods which 
minimize the problems of an "infection-free" 
interface. In addition, material is presented 
which covers aspects of an electrode system 
suitable for chronic recording and stimulation. 
Methods of minimizing the disadvantages as- 
sociated with telemetry are discussed elsewhere. 
The following text is separated into three sec- 
tions. The first is concerned with methods which 
can be used to minimize the problems of main- 
taining an "infection-free" interface. The sec- 
ond and third sections cover test results with 
an electrode configuration found to be suitable 
for long-term use and methods of connecting 
this electrode to a lead wire respectively. The 
material in the latter two sections is applicable 
to systems utilizing either telemetry or per- 
cutaneous wires. 
THE INTERFACE 
A major problem encountered with percu- 
taneous wiring is the maintenance of an "infec- 
tion-free" interface. The term "interface" is 
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