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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



the results of the injections. This has been accom- 

 plished by some who have standardized an injection 

 mass that does not penetrate through vessels of less 

 than a known diameter. Important information has 

 been \ ielded by such radiopaque materials as Schle- 

 singer's (154, 155). Colored masses in gelatin or simi- 

 lar materials have also been used to inject tissues 

 that have subsequently been cleared, for example by 

 the method of Spalteholz (164). Materials that 

 harden to provide casts of the vessels and which 

 resist subsequent corrosion of the tissues have been 

 useful in many applications. In the study of such 

 casts, or other injections, certain critical points can 

 be established, and the magnitude of the collateral 

 can be estimated by whether or not the material has 

 penetrated into particular segments of the system 

 (147). Casts can be measured or weighed. Glass or 

 plastic beads of graded sizes have been used to es- 

 tablish the size of vascular communications (2, 3, 

 126, 131, 137, 138, 162). With these materials over- 

 pressure must be avoided and the possibility of con- 

 tamination must also be considered. Angiography, 

 microangiography (11), and more recently cineange- 

 ography have become increasingly important with 

 improvements of technique, especially since they 

 offer a way of investigating the collateral circulation 

 in intact animals. Quantitation can be achieved by 

 such procedures as that of Longland (108), who 

 counted the number of vessels in his angiograms that 

 exceeded a stated size at a selected level. In the lung, 

 a degree of refinement can be obtained by relating 

 the vessels to the diameters of the bronchi which they 

 accompany (188). The same can be done in any 

 organ with an appropriate reference structure. 



To measure collateral blood flow, direct and more 

 or less indirect methods have been applied. The 

 simplest perhaps is the collection of blood from the 

 veins draining the part. This procedure is useful only 

 if the tissue is supplied exclusively from a collateral 

 source during the period of measurement, and if the 

 veins carry away all or a known proportion of blood. 

 These conditions cannot often be met. In man, 

 plethvsmography has been employed in the study of 

 collateral circulation (193). 



The collection of "backflow" from a vessel beyond 

 a point of occlusion has been used on the presumption 

 that it will increase if the vessels circumventing an 

 occlusion come to carry an increased volume of 

 blood. This principle has been extensively applied in 

 the study of the coronary circulation (63). Upon 

 opening the vessel beyond the obstruction the periph- 



eral resistance confronting the blood in the collateral 

 vessels is, of course, reduced, and the backflow can in 

 no sense be considered an absolute measure of col- 

 lateral blood supply. As a relative measure the prin- 

 ciple is valid if no uncontrollable change, such as 

 spasm, has occurred in the diameter of the vessel 

 beyond the point of occlusion. Backflow then would 

 reflect the pressure in the vascular bed in the distal 

 arterial segment, which also is related to the extent 

 of the collateral connections. Pressures as well as 

 flows have been measured for this purpose. 



Other "'direct" measurements have been made by 

 introducing such devices as the bubble flowmeter 

 into the major feeders of the collateral bed (26). 

 In such structures as the lung, attempts have been 

 made to perfuse separately the greater and lesser 

 circulations (151). Both procedures require extensive 

 surgery, with denervation and possibly other dis- 

 turbing factors. 



In the lungs bronchospirometry and blood gas 

 analyses, with temporary balloon blockade of a pul- 

 monary artery and application of "mixing formulas" 

 where indicated, can provide data on "'effective" 

 collateral arterial flow, i.e., blood arriving by syste- 

 mic arteries that becomes oxygenated in the lungs 

 (20, 52). 



The fact that the temperature of a tissue bears a 

 relationship to the quantity of arterial blood perfusing 

 it in a unit of time has been used to measure col- 

 lateral circulation (50). One source of error lies in the 

 fact that blood flow is not necessarily distributed in a 

 uniform manner through all tissues of a part, nor 

 through all portions of a tissue. 



The distribution of such dyes as Evans blue or Fox 

 green or of radioactive materials, or "labeled" 

 ervthrocytes (138) in various vascular compartments 

 has been used for qualitative detection of shunts, but 

 under specific conditions. Isotonic solutions differing 

 in temperature or conductivity from blood can be 

 employed instead of dyes, and records similar to dye 

 concentration curves can be obtained with appro- 

 priate sensing, amplifying, and recording devices. 



Under special circumstances such methods can 

 also be applied in a quantitative fashion. In the lung 

 where an extensive bronchial collateral circulation 

 represents a left-to-left shunt, originating as it does in 

 the left ventricle and aorta, and returning from the 

 lungs via the pulmonary veins to the left heart, intro- 

 duction of an indicator material such as T-1824, 

 Fox green, or radioactive iodinated serum albumin 

 into the circulation produces characteristic altera- 



