A SURVEY OF THE APPLICATIONS OF ELECTRONICS 



IN MEDICINE 



G. E. DONOVAN, M.Sc, M.B., D.P.H. 

 Public Health Department^ Gorseinon^ Swansea 



Introduction 



ELECTRONICS in medicine covers such a large field that, 

 in this article, only some of the more important and interest- 

 ing aspects of the subject can be dealt with. There is hardly 

 a branch of medicine which cannot benefit from the application 

 of electronics. 



The phenomena with which a physician has to deal — sound, 

 pressure, heat, etc. — can easily be transformed into electrical 

 equivalents which can be amplified by thermionic-valve ampli- 

 fiers, and graphically recorded. Bioelectric quantities, such as 

 the electrical variations of the heart, lend themselves readily to 

 valve-amplifier technique and registration. The extent of ampli- 

 fication of the signal is governed by the amplification given by 

 the valves in the various stages, and is modified by the attenua- 

 tion which occurs as a result of the relationship of signal fre- 

 quency to the resistance-capacity values used for coupling. This 

 relationship is the frequency response characteristic of the 

 amplifier. 



The amount of useful amplification really depends on the 

 "resolving power" of the amplifier, i.e., the smallest potential 

 change that can be detected, and this in turn is mainly dependent 

 on the working of the first stage of the amplifier. At present 

 we can detect an input change of one microvolt in a circuit of 

 high resistance, like a small nerve trunk, but it is difficult to 

 deal with anything less than this because of fluctuations intro- 

 duced by the resistors, valves, etc. 



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