1260 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



VEIN 

 CAPILLARIES 



ARTERIAL BRANCHES 



■ MAIN ARTERY 



VEIN 

 CAPILLARIES 



COLLATERAL ARTERY 



— MAIN ARTERY 



fig. 6. Longland's (108) concept of the stem and re-entrant 

 vessels and midzone in a collateral circulation after occlusion 

 of an artery. 



lateral circulations: In the first type, after a short 

 course in alternative channels, the arterial blood is 

 returned into the main artery or arteries of the part. 

 In the second type blood reaches the part beyond an 

 obstruction via terminal branches only; here the 

 pressure is low and quantity probably reduced. In 

 duodenal transplants, North et al. ( 1 28) found that in 

 some instances only numerous fine extramesenteric 

 vascular connections had formed, while in others the 

 connecting channels were quite large. 



Forces Affecting the Development of Collateral Circulation 



In the general consideration of angiogenesis there 

 emerged at least three significant types of influences: 

 hereditary, mechanical, and chemical; moreover, the 

 responses of vessels once formed are governed also by 

 the action of nerves. These same forces affect col- 

 lateral vessels. Their immediate responses must be 

 considered separately from late responses. 



mechanical factors. The fall in pressure peripheral 

 to the interruption of a major artery may have 

 mechanical or chemical effects that could stimulate 

 the development of collateral circulation. The idea 

 of a chemical mechanism, especially anoxic, was 

 strongly championed by Sir Thomas Lewis (98). 

 The one does not necessarily exclude the other. 







16 



4 8 12 



WEEKS AFTER ARTERIAL BLOCK 

 fig. 7. Mean growth rates of stems and midzones {% increase 

 per month of initial diameter [= 100%]). The relatively greater 

 growth of the midzone as compared with the stem vessels in a 

 collateral system as established from measurement of angio- 

 grams. Data from 7 rabbits. [From Longland (108).] 



Manv attempts have been made to assess the relative 

 impact of the two. 



Winblad and associates (192) measured both pres- 

 sure and pO a in an extremity of the dog in which the 

 superficial femoral artery was acutely occluded. 

 There was a quick drop in pressure to between 35 

 and 60 mm Hg. After 4 min the pressure level re- 

 mained constant, with the systolic pressure exceeding 

 the diastolic before occlusion (fig. 8). Widening of the 

 collateral vessels was demonstrated angiographically. 

 The pOo of the tissue fell only very slightly, and rose 

 again to control values within 5 to 8 min. The rate 

 of recovers' was not affected, whether the artery 

 distal to occlusion was perfused with highly oxy- 

 genated or venous blood by means of an artificial 

 pumping system. Similar experiments were per- 

 formed by John & Warren (90) with like conclusions. 

 The rapid appearance of the collateral vessels was 

 also demonstrated angiographically, as was their 

 quick regression when continuity of the main artery 

 was restored. These observations suggest the relative 

 importance of mechanical factors. Volpel (184) 

 found that with repeated interruption of the femoral 

 artery the blood pressure in the distal segment would 

 rise more rapidly. By creating a shunt between the 

 left femoral artery and right femoral vein, and inter- 

 rupting the left femoral artery below the arteriovenous 

 connections, collaterals did not des'elop; but if the 

 shunt were interrupted they quickly reappeared. 

 However, in the distribution of the right femoral 

 artery the collaterals became visible upon its occlu- 

 sion as in the absence of a shunt. Further, if the distal 



