CHAPTER XXX 



CLINICAL APPLICATIONS OF CERTAIN PHYSIOLOGICAL 



METHODS* 



(Revised by N. B. Taylor) 



In the following chapters a brief account will be offered of the clinical 

 use of the electrocardiogram, of polysphygmograms, and of bloodflow 

 measurements. This is done to show how physiological technic is being 

 employed for the accurate investigation of cardiovascular disease. 



ELECTROCARDIOGRAMS 



To observe the electrical change produced by the spread of the excita- 

 tion wave over the heart from auricles to ventricles, it is not necessary 

 to place the electrodes directly on the heart, but, as already hinted, we 

 may follow the electrical change by leading off from electrodes applied 

 to the surface of the body. From such electrocardiographic tracings 

 extremely important facts concerning the propagation of the heartbeat 

 may be ascertained. In order to make an observation the hands and the 

 left foot are each placed in a solution of sodium chloride contained in 

 porous jars, immersed in larger vessels containing a saturated solution of 

 ZnS0 4 and zinc terminals.! An arrangement like that in Fig. 81 may also 

 be used. By manipulation of suitable keys, the extremities may then be 

 connected with the electrocardiograph in the following manner : Lead I, 

 right arm and left arm; lead II, right arm and left leg; lead III, left arm 

 and left leg. 



When any pair of leads is connected with the galvanometer, it is ob- 

 served that the string is deflected to one side owing to electrical cur-' 

 rents arising from the skin. Before taking a record of the cardiac 

 movements of the string, it is necessary to compensate for this skin cur- 

 rent by introducing into the circuit in the opposite direction the re- 

 quired amount of current, called the compensating current, to bring the 

 string shadow back to the zero or midposition. In order that the rec- 

 ord obtained may be quantitative in character, it is further necessary 

 that the movement of the string be standardized. This is done by as- 



*A certain amount of repetition of matter previously discussed has been found advisable in these 

 chapters for which the indulgence of the reader is requested. 



tit is really unnecessary to use the so-called nonpolarizable electrodes. Glass vessels containing 

 20 per cent NaCl solution with the zinc plates dipping into them are quite satisfactory. 



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