CHANGES IN VASCULAR PATTERNS 



tions from the usual in the arterial dye curve: A more 

 rapid reversal of the downward limb of the first wave 

 and a double-humped camel rather than dromedary 

 recirculation curve. A known quantity of the indi- 

 cator can be injected rapidly into a systemic vein, 

 and concentration curves can be obtained simul- 

 taneously from the pulmonary artery and aorta by 

 appropriate methods such as cuvette densitometry. 

 The "left cardiac output" measured from the latter 

 should exceed the "right cardiac output" calculated 

 from the former by the volume of the collateral blood 

 supply to the lung. This principle has been applied 

 by a number of workers (38, 55, 56), but very rapid 

 left-to-left recirculation introduces problems that 

 may make this procedure inapplicable for quantitative 

 use. 



To measure collateral blood flow from extra- 

 coronary sources to the heart by means of vessels in 

 anastomosis with the coronary arteries, the dye has 

 been introduced into the aorta above the orifices of 

 the presumed collaterals and well below the origins 

 of the coronary arteries in the sinuses of Valsalva. 

 If collaterals exist, dyed blood will reach the coronary 

 sinus by the collateral route before recirculation can 

 take place. Quantitation has been attempted by com- 

 paring the peak concentrations in the aortic blood 

 with that of the coronary sinus peak, or better, the 

 areas beneath appropriate segments of the two 

 curves (182). 



Some Outstanding Problems 



The problems of collateral circulation are in- 

 separable from those of angiogenesis, "histodynamic->" 

 in Thoma's sense and hemodynamics in general. 

 Methods for study have advanced notably, but new 

 developments can be expected to accelerate progress. 

 Catheters, as used currently for measuring pressures 

 and in obtaining dye concentration curves, carry 

 inherent artifacts. Accurate sensing units sufficiently 

 small so as not to interfere significantly with blood 

 flow are needed for both purposes 



It is clear that many of the basic mechanisms must 

 be essentially physicochemical. These must underlie 

 the molding influence of mechanical forces on the 

 structures of vessels. They must also be responsible for 

 what is now vaguely recognized as "tropism." None 

 of the essential chemical information is yet available 

 to explain how, in a newly formed collateral bed, 

 arteries are joined directly to arteries and veins to 

 veins, with no arteriovenous connections, while the 

 latter are constantly present normally in certain 

 other parts. 



John Hunter's (185) remark of 1785 still well 

 defines the present state of knowledge: "All the uses 

 arising from the anastomosing of the vessels are, per- 

 haps, not yet perfectly understood; general reasons 

 can, I think, be assigned for them, but these will not 

 apply to all cases; it is something, therefore, more 

 than we are yet acquainted with." 



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