288 - 



THE CIRCULATION 



any given patient's pulse, the more valuable will be his estimate as an 

 index of the latter 's condition. The trained physician and surgeon 

 take practically all of these variants into consideration without realizing 

 it perhaps, but they none the less on that account affect the estimate. 



The Cardiac Sequence comprises the various contractile events in one 

 complete beat of the heart and their time-relations. This "cycle" 

 extends from the beginning of one auricular systole to that of the next. 

 We will take the average rate of 75 beats per minute and see how the 

 various parts of the heart are differently using these beat-periods. At 

 this rate each beat occupies one seventy-fifth of sixty seconds or 0.8 

 second, and tenths of a second are also eighths of a beat-period, as it 

 very conveniently happens. The systole of the auricle (or auricles, for 



FIG. 154 



PULSE 75 PER MINUTE. 



The cardiac sequence. One beat out of the continuous series. The lighter areas, 

 contraction (systole); the darker areas, rest or relaxation (diastole). 



the two contract almost exactly together, as do the two ventricles) occu- 

 pies, at this pulse-rate, 0.1 second. Immediately begins the systole of the 

 ventricles, and this requires 0.3 second, which, added to the 0.1 second, 

 makes 0.4 second, or half of the 0.8 second which the beat requires. 

 The other half of the 0.8 second, 0.4 second, is part of the whole heart's 

 rest-time. During this period, as well as during the 0.1 second of the 

 succeeding auricular systole, the ventricles are in restful diastole while 

 being slowly filled with blood from the auricles and great veins. Thus, 

 the ventricles work in each beat-period 0.3 second and rest the remainder 

 of the beat-period, 0.5 second. The auricles work only 0.1 second 

 (if we disregard the possibility of an active diastole), and rest during 

 the remaining 0.7 second, while the ventricles are both contracting and 

 resting. Thus the auricles work one-eighth of the time and rest seven- 



