PULSATILE BLOOD FLOW 



845 



and overemphasize the regularity of the heart rate. 

 Also, the terms of a series such as the Fourier have no 

 real physiologic meaning and in fact may fail to show 

 a dominant and important frequency such as the 

 arterial resonant wave. 



III. SYSTEMIC ARTERIAL FLOW 



Shipley et al. (44) and Pritchard et al. (37) made 

 one of the most comprehensive recordings of the 

 arterial flow pulses using the differential pressure 

 flowmeter. They offered no fundamental theory to 

 explain the recorded phasic pressure-flow relationship. 

 Although some exception may be taken to their flow- 

 meter, the general form of the flow pulses agrees well 

 with more recent electromagnetic noncannulating 

 recordings. 



Blood Flow in the Ascending Aorta 



The arterial network is pulsed by a flow pulse from 

 the left ventricle normally of the configuration in 

 figure 6. This recording is taken with the square-wave 

 electromagnetic flowmeter on the ascending aorta, 3 

 to 5 cm distal to the aortic valve. What were ap- 

 parently the first accurate phasic recordings were 

 made by Wetterer (58). The linear acceleration of the 

 blood by the left ventricle is remarkable, reaching 

 greater than 8000 cm per sec per sec in an anesthe- 

 tized open-chest dog (47). At the end of acceleration, 

 the velocity of the blood in the ascending aorta may 

 easily exceed 100 cm per sec in the resting state. 

 Deceleration takes place at a rate approximately one- 

 sixth of acceleration until closure of the aortic valve 

 when a sharp notch of deceleration and acceleration 

 brings the flow to nearly zero for the duration of 

 diastole. 



For many practical purposes this flat "uneventful" 

 tracing during diastole in the ascending aorta may be 

 used as a zero flow reference to compute the stroke 

 volume. The fact that coronary flow is not included 

 may produce a small unknown error. Apparently, the 

 diastolic flow curve in the ascending aorta is flat at 

 nearly zero because the reversing effect of coronary- 

 flow is balanced by the forward effect of decompres- 

 sion of the first portion of the ascending aorta. The 

 left ventricular ejection velocity at the root of the 

 aorta recorded by Pieper (fig. 7) is similar to the flow 

 pulse throughout the ascending aorta. Since this 

 instrument records the axial velocity, it appears that 

 the velocity profile of the ascending aorta is relatively 



0.5 sec 



fig. 6. Flow pulses in the ascending aorta of an unanesthe- 

 tized dog. C-core electromagnetic probe was implanted 6 weeks 

 prior to this record on the ascending aorta. Electrical connec- 

 tions were made by means of implanted subcutaneous wires, 

 brought to the surface through a small superficial incision. 



Aortic Pressure 

 133 mm Hg 



fig. 7. Axial flow pulse in the ascending aorta recorded by 

 means of velocity probe situated in midstream. [From Pieper 

 (36).] 



flat. More backflow occurs here during early diastole 

 presumably because of diastolic coronary flow. 



The effect of exercise on the ventricular ejection 

 pulse is illustrated by a remarkable experiment by 

 Olmsted (personal communication), figure 8. The 

 animal had a magnetic probe implanted on the as- 

 cending aorta and an arrangement for remote pres- 

 sure recording. After one month's recovery from the 

 surgical procedure he was exercised by running in a 

 harness behind a station wagon carrying recording 

 equipment. Suitable wiring carried the electrical 

 signals between the automobile and the dog. The 

 course was one-half mile over rough terrain at an 

 average speed of 10 mph. Upon standing, the cardiac 

 output increased primarily because of increased 

 heart rate without change in stroke volume and with 

 little change in form of the ejection pulse. Running 

 at 5 mph increased cardiac output by increasing both 



