376 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



about the y axis is pictured, and the final angle 6 

 necessary to produce this \iew measured. With 6 set 

 at this reading, the system is then rotated in the 

 craniocaudal direction around the newly established 

 x' axis to produce again an edgewise view. With 

 added 90° of rotation, the loop is again seen broad- 

 side, and the ele\-ational angle a recorded (444). 



The loop (if planar) may be simply described by 

 its "polar vector" in the following way. The polar 

 vector stands perpendicular to the plane of the loop 

 and, starting from the zero point, is drawn on the 

 side from which the rotation is seen to be counter- 

 clockwise. The length of the vector indicates the 

 area of the loop (146). The projection of this polar 

 vector on the horizontal plane has an azimuthal angle 

 between go° and 180° (it appears backward and to 

 the left). The angle of the vector with respect to 

 the y axis is i^etween 0° and —90°; the vector being 

 directed upward, and the loop therefore oriented 

 downward (146). (Angles measured as in fig. 58.) 



Viewed from the "edge" of its plane, the loop may 



FIG. 59. Some examples of normal loops, recorded with the 

 Grishman cube (fig. 20). Note that the saggital plane is viewed 

 from the right. [From Gri.shman & Scherlis (28).] 



be analyzed in the following way. The distance 

 between two parallel lines enclosing the narrowest 

 view of the loop obtainable by either azimuthal or 

 elevational rotation may be called the "edgewise 

 width." The ratio of this edgewise width to the 

 longest vector in the broadside view is called the 

 "planarity." Its average values lie between o.ii and 

 0-I3 (347> 444)- These data alone would permit an 

 ample description of the loop; however, the electronic 

 devices necessary to resolve the ECIG in such a manner 

 are not available in many laboratories. Moreover, 

 such a description of the loop's plane does not contain 

 any information about the form of the loop (the 

 openness excluded), the direction of the maximal 

 vector (the electrical axis), and the time course of all 

 electrical changes. Therefore, the planar projections 

 of the loop in an orthogonal reference system will in 

 most cases remain the method of preference, though 

 the foregoing analysis is an excellent method for 

 standardizing the general peculiarities of such loops. 

 The normal form of the Q.RS vector loop is rather 

 simple: a wide open planar loop with smooth con- 

 tours, without crossovers, and invariably transcribed 

 counterclockwise when looked at from a direction 

 normal to its respective planes, from above and left 



(444)- 



A detailed description of the form of loops is 

 possible in every projection of the spatial loop. One 

 may distinguish the "initial forces" of the loop, the 

 loop "body," and the terminal "appendage." Initial 

 forces and appendage are arbitrarily distinguished 

 from the body thus: the body of the loop begins 

 when the vector passes to the left and below the zero 

 point (537). Initial forces and appendage are more or 

 less identical with Q and S. 



An additional analysis of the loop involves measur- 

 ing the time the sector needs to rotate from one-half 

 of its maximal value in the rising phase over the 

 peak, to one-half of the falling phase. This time lies 

 in most cases, between the limits of 15 to 30 msec, 

 with an average of 23 m.sec. The central angle sub- 

 tended by this segment of the loop ax-erages 41°, and 

 the mean angular velocity of the rotating vector 

 varies Ijetween 16 and 21 degrees per 10 msec, with 

 a range between 3 and 40 degrees per 10 msec. 

 This angular velocity seems to be a measure of 

 normality and diminishes in cardiac patients (458). 



The form of the horizontal projection of the vector 

 loop, in combination with the surface image in the 

 horizontal plane as shown in figure 60, explains full\- 

 the precordial lead records, as given in figure 52. 

 The horizontal loop of figure 60 is directed mainly 



