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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



and the contour is not one we would regard as repre- 

 sentative of that to be obtained from an animal in 

 good circulatory condition. The ascending aorta and 

 arch are taken as the first tube segment. From our 

 tabulated pressure-volume tables (104) a volume up- 

 take curve can be constructed for this segment in 10- 

 msec intervals, starting at the time the central pressure 

 pulse begins its upstroke. Because, in the Wetterer 

 experiment, the ascending aorta had a flowmeter 

 attached, we have arbitrarily reduced the volume 

 uptake of this segment by one half. Rather than 

 plotting the total uptake, only the net gain or loss of 

 volume for each time interval is given as the solid 

 line curve of figure yB. While the pressure in this 

 segment is still rising, the volume will be increasing. 

 When the pressure falls in late systole, there will be 

 a net loss of volume. 



The thoracic aorta and head and foreleg arteries 

 are grouped together in the next part of the funnel, 

 and it takes the wave some 30 msec to move through 

 the whole. Hence, for uptake calculation the total 

 region is divided into three parts, displaced 10 msec 

 behind each other. The summed net volume change 

 for all three is given by the broken line, labeled H, 

 in figure yB. Next, the pressure wave invades the 

 abdominal aorta and visceral arteries, which takes 

 another 30 msec. The summed volume change of 

 the three units involved is given as the dotted line 

 (V). Finally, the summed changes of the three leg 

 vessel units are given in curve L. Flow through the 

 ascending aorta must not only accomodate the volume 

 acceptance of more distal arteries, but must supply 

 systolic drainage through the arterioles as well. The 

 calculation of this latter will not be gone into here 

 (see ref. 44), but it is indicated in figure ~]B by curve 

 D. Ascending aorta flow now should equal the alge- 

 braic sum of all these curves at any given time in- 

 stant. The value obtained is per square meter of 

 body surface. It is assumed that the dog Wetterer 

 used was medium size, i.e., had about 0.6 m 2 surface 

 area. The use of this assumed value means that we 

 should not expect quantitative agreement between 

 the derived curve and the actual one, but only 

 qualitative agreement. The total flow calculated in 

 the above manner is given as the broken line in figure 

 yC. The actual curve presented by Wetterer is given 

 by the solid line. The calculated values therefore 

 indicate a flow increasing more steeply in early 

 systole, and decreasing sooner and more sharply after 

 the peak. This discrepancy in flow might have four 

 causes: /) the flowmeter might be slurring the actual 



curve; 2) there might be a distortion of the aortic- 

 flow curve because of vessel constriction produced by 

 the meter; 3) there might be a true time lag, of ap- 

 preciable proportions, between the pressure curve and 

 the flow curve; and j) wall hysteresis might change 

 the form of this calculated flow curve. The influence 

 of the last of these can be directly tested. If the volume 

 uptake values are calculated from a hysteresis loop of 

 the same pattern as those given in figure 3, the 

 rate of volume gain in early systole would be de- 

 creased, and there would be little volume change 

 while the pressure first starts its fall in late systole. 

 The summed flow curve, as given in figure 7C by 

 the dotted line, differs but little in form from that 

 given by the broken line. Hence it would be difficult 

 to reconcile the calculated curve with the actual with 

 even a large amount of vessel hysteresis. 



A similar calculation was done for the only three 

 pulses presented by Spencer and co-workers (119, 

 120) which have accompanying pressure pulses. 

 The flow recorder here was on the upper thoracic 

 aorta, so that the uptake of the arch, head, and 

 foreleg vessels were omitted when the volume changes 

 were summed to give the flow curve. The same type 

 of discrepancy between the calculated and the re- 

 corded flow pattern is again seen (fig. 8). It might 

 be noted that these pressure pulses are unusual in 

 that they have a very steep initial rise in pressure, 

 with a relatively flat systolic crest. This might be 

 evidence of an effective aortic constriction by the 

 meter. If so, the flow profile in the lower aorta would 

 not be expected to match the form of this pressure 

 pulse. 



On the premise that flow should lag behind the 

 instantaneous pressure, Fry and co-workers (34) 

 derived an equation in which the pressure difference 

 between two points in the aorta was equated to the 

 sum of an inertial term and a factional resistance. 

 Solution of their equation was achieved by use of 

 an electronic computer. After checking their equa- 

 tion by use of a sinusoidal pump with a tube (rigid?), 

 they proceeded to construct a flow velocity curve 

 for the upper aorta, using catheter tips 6 cm apart 

 for the pressure recordings. Xot knowing the exact 

 positions of the catheters, one is uncertain as to 

 just what vessel segments should be included in an 

 attempt to construct a similar flow curve on the 

 basis of vessel distensibility. We used the whole 

 aorta, as though we were calculating a cardiac 

 ejection curve. Xot knowing dog size or diastolic 

 aortic dimensions, the calculated peak flow value was 



