PHYSIOLOGY OF AORTA AND MAJOR ARTERIES 



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fig. 12. A mapping of the change in pulse form in the dog 

 aorta. Pulses from ascending aorta (/t), descending arch (4), 

 upper thoracic aorta (7), mid thoracic aorta (10), lower 

 thoracic aorta (14), abdominal aorta (18) and iliac artery (22). 

 [From Remington (100).] 



The German workers have also been concerned 

 about the effect the large visceral arteries might have 

 on the resonant wave. They (58), like Hamilton, 

 would locate the only significant reflection point in 

 the small arteries. The influence of any single aortic 

 branch as an independent reflection unit (particu- 

 larly that of a vessel so far proximal to the "end" of 

 the system as a visceral artery) causes them no great 

 concern. Assuming the resonant frequency to be 

 already established (they have presented no analysis 

 as to how this might be achieved), they conclude that 

 reflections in this branch would serve to augment the 

 pressure excursion without altering the fundamental 

 wave length of the incident wave. An example of 

 this is seen when two manometers of different fre- 

 quency response record in parallel a rapid pressure 

 change; the records from both will be the same and 

 reflect the response characteristics of the slower 

 manometer. This would not explain Alexander's 

 preincisural trough seen on the central pulse. 



In a number of mappings of the dog aorta (99) 

 I found that while in some pulses the late systolic 

 trough could be seen, it was not present in pulses 

 taken from the descending arch of thoracic aorta 

 (fig. 12). Hence this trough apparently is not prop- 

 agated back from the upper abdominal aorta, but 

 rather appears de novo in the ascending aorta pulse. 

 Although there were some time discrepancies be- 

 tween the systolic peaks of the peripheral aortic 

 waves, there was a general tendency for a standing 

 wave to occur. But this standing wave seemed to 

 develop as a sinusoidal swell taking off from the 

 broad crest of the propagated wave, and appeared 

 first in the aortic arch or at least high in the thoracic 

 aorta. Its size progressively increased as the wave 

 moved toward the periphery. If this swell represented 

 the first of a resonant wave, we would have to con- 

 clude that the node for this first peak was within the 

 aortic arch itself. This swell developed at about the 

 same time that the foot of the incident wave reached 

 the femoral artery. Later reciprocal oscillations be- 

 tween ascending aorta and lower abdominal aorta 

 could be seen, with minimal pressure change in the 

 upper thoracic aorta. The node of these oscillations 

 would thus appear to be more distal than that for 

 the systolic peak. All that we can conclude is that 

 the genesis of aortic resonance remains obscure. 



Other Factors Which May Alter the Central Pulse Contour 



Fascinating as this whole problem of resonance 

 may be, it certainly is not the sole factor which may 

 produce contour change and pulse pressure change 

 when the pulse of the ascending aorta is propagated 

 to the lower aorta or to the brachial artery. Possible 

 factors which may bear on these changes are: 



a) A loss of sharp inflections and an attenuation of 

 the pulse pressure might result from damping. In a 

 distensible tube such damping is due in part to fluid 

 friction, but probably much more to a conversion of 

 energy from kinetic to potential form because of the 

 extension of the walls, with a delayed recoverability 

 of this energy because of the visco-elastic properties 

 of the wall. Clear illustrations of such a reduction in 

 pulse pressure and lengthening of the systolic wave 

 contour during propagation can be seen in dogs with 

 a deteriorated circulation, or at least a weakened 

 heart, after the use of a strong vasodilator agent (94) 

 and when the rate of flow from the upper aorta to 

 the lower is severely reduced, as by a partial occlu- 

 sion (23). 



b) A peaking of the pulse contour could follow a 



