THE CARDIAC IMPULSE. 



37 



bottom of the descending limb of the impulse curve, marked / in 

 Edgren's tracing. 



By Hilbert 1 the second sound is placed earlier at the beginning 

 of the descending limb of the curve. 



The second sound does not mark the exact moment of closure of the 

 semilunar valves, but the time at which these valves are thrown into 

 tension by the back swing of the blood. Synchronous or differential 

 curves of intraventri- 

 cular and aortic pres- 

 sure show that the 

 valves shut earlier 

 than the occurrence 

 of the second sound, 

 and without noise, at 

 the moment when 

 the aortic pressure 

 rises to a point 

 higher than the in- 

 traventricular pres- 

 sure. 



Another method 

 of obtaining the 

 moment of closure 

 of the semilunar 

 valves on the im- 

 pulse curve is as 

 follows : 



The cardiac im- 

 pulse and carotid or 

 radial pulse curves 

 are simultaneously 

 recorded. The time 

 relation of the bottom 



Sy-sfole. 



FIG. 25. Both high and low aortic pressure curves 

 are shown. Hiirthle. 



of the dicrotic notch 

 is then marked upon 

 the impulse curve. 

 The time lost in the 



transmission of the pulse-wave from the heart to the artery where 

 the pulse is recorded must be first deducted. By the observa- 

 tions on intraventricular and aortic pressure, curves it has been 

 abundantly proved that the dicrotic notch occurs immediately on the 

 closure of the valves, and synchronously with the commencement of 

 the downstroke of the intraventricular pressure curve. Fredericq 2 has 

 thus found that the dicrotic notch corresponds in time with the begin- 

 ning of the downstroke of the impulse curve, and he believes that the 

 nick, which occurs synchronously with the second sound at the bottom 

 of the descending limb of the cardiogram, is caused by the inflow of 

 blood into the ventricle at the commencement of diastole. The waves 

 on the top of the plateau of the cardiogram have no doubt the same 



1 Ztschr.f. klin. Med., Berlin, 1891, Suppl. Heft, Bd. xix. S. 158. Cf. Bramwell and 

 Murray, Brit. Med. Journ., London, 1888, vol. i. p. 10; Martius, Ztschr. f, klin. Med., 

 Berlin, 1891, Bd. xix. S. 108. 



2 CtntralbLf. PhysioL, Leipzig u. Wien, 1892, Bd. vi. S. 257, 



