1913.] 



Electrical Axis of the Human Heart. 



519 



where I first noticed that the correction might be required, and I have 

 therefore thought necessary to say that I have been alive to the error that 

 might be made by neglecting the correction where it was evidently of 

 moment. 



The type of the electrical pulse by different leads is remarkably individual 

 and constant. Thus it has not altered, as far as I can tell, in the cases of 

 A. D. W. and A. M. W. and T. Goswell between 1887 and 1913. 



Nevertheless, temporary variations do occur in a given individual — varia- 

 tions of frequency of course, but also variations of form and variations of 

 the angle «. I think that such variations are attributable to greater and 

 lesser repletion of the stomach and of the several cavities or of the two 

 sides of the heart. In at least two instances where the angle a has been 

 found greater in the same individual at one time than at another, I have 

 associated the value of the angle with the state of health. But the dis- 

 cussion of this important point cannot profitably be entered upon until the 

 effect of respiration has been fully considered ; and it properly belongs to a 

 future communication on the pathological significance of the angle a.* 



7. The Influence of Muscular Exercise. 



As was to be expected, the frequency and character of the electrical pulse 

 are altered with muscular exertion. 



Electrocardiograms afford indeed the most convenient available means of 

 exactly counting the pulse, and of measuring out the working-time of the 

 heart from varying relations between length of systole and length of 

 diastole. But the primary object of this paper is to study variations of 

 the angle a, and in this connection it appears that any variations that 

 might be expected to result from variations of repletion of the several 

 cavities is masked by the large variations caused by deepened respiration — 

 especially inspiration. The detailed consideration of the influence of 

 exercise must therefore be subordinated to that of the influence of respiration, 

 and at present it will be sufficient to give the results of observation on one 

 subject (B. 0. B.) in illustration of the fact that muscular exertion indirectly 

 through modified respiration, and perhaps also directly by modifying the 

 repletion and shape of the heart, does actually bring about considerable 

 modifications of the electrocardiogram and of the angle a as calculated from 

 its right and left hand values. 



* A further complication arises where the left lateral lead is negative ; the correction 

 has then to be taken in the opposite sense, because whereas a positive left lateral is 

 increased with inspiration, a negative left lateral is diminished. The same holds good for 

 a negative right superior record. But the discussion of these points must be postponed. 



