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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



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2 mm 



fig. 1 1. Trend lines of curves showing relation of diameters of 

 bronchia] arteries (ordinate) to bronchi and bronchioles which 

 they accompany (abscissa), as calculated from observations in 

 individual rats. Between the 5th and 10th days there is a sudden 

 increase in slope. This corresponds in time to the onset of proli- 

 ferative activity in the walls of the collateral vessels. [From 

 Weibel (188).] 



collateral circulation after interruption of the left 

 pulmonary artery in the rat also provide information 

 on mechanisms (188). The process appears to be 

 biphasic, with initial mechanical expansion, followed 

 by active proliferation of vessels. This is reflected in 

 quantitative observations on the size of bronchial 

 arteries as related to the bronchioles which they 

 accompany. In the first phase the arteries increase in 

 diameter, but the ratios to the diameters of the 

 bronchioles have approximately the same slope, sug- 

 gesting simple mechanical expansion (fig. 11). Be- 

 tween the fifth and tenth days, the slope suddenly 

 becomes much more steep. Histologically, at about the 

 fifth day mitoses begin to appear in large numbers 

 both in endothelial and muscle cells, indicating that 

 active proliferation is in progress. The new cells appear 

 as solid sprouts that seem to extend to their desti- 

 nations in the capillary beds of the alveoli before they 

 acquire a lumen. At the proximal end of the ligated 

 pulmonary artery the collateral vessels actually pene- 

 trate the thick musculo-elastic wall to establish 

 anastomoses which do not normallv exist in rats 



(180). All of these observations suggest the effect of 

 chemical influences. 



Rate of Developmi tit 



The immediate expansion of pre-existing arterial 

 collaterals has been demonstrated angiographically 

 by a number of observers, for example, Winblad et al. 

 (192), John & Warren (go), Longland (108). That 

 persistent sympathetic activity can produce some 

 delay has been shown by Ferris & Harvey (50) and 

 by Mulvihill & Harvey (125), among others. The 

 existence of a later and slower phase of growth has 

 been realized for a long time. For example, in Noth- 

 nagel's (129) experiments it took at least 6 days after 

 interruption of the femoral artery below the pro- 

 funda and circumflex in rabbits, before Teichmann's 

 injection mass could be made to penetrate beyond 

 the ligature. Mention has previously been made of 

 the sudden increase in relative size of the collateral 

 vessels, as compared with the bronchi as a reference, 

 after the fifth day following ligature of the pulmonary 

 artery in the rat (188). 



Quantitative flow data are relatively sparse. The 

 problem was approached in various collateral beds 

 by Eckstein et al. (47) using as a measure not only 

 the pressure beyond a point of occlusion, but also the 

 retrograde flow at intervals varying from less than 

 1 hour to many months. In general, in the femoral 

 and carotid distributions, the collaterals opened 

 rapidly, for example, to near maximal levels within 

 1 hour, while the process took several hours to a week 

 to attain a comparable relative increase in the 

 coronary circulation. When both the femoral arteries 

 and veins were ligated there was an increase in retro- 

 grade pressure and flow as previously observed by 

 Holman & Edwards (78), and Eckstein et al. (47) 

 found the same to be true in the coronary arteries 

 upon ligature of the coronary sinus. The conservative 

 effect on tissue of ligating the corresponding vein 

 when a major artery is interrupted has been stressed 

 by Makins (ill) and confirmed by Reichert (143). 



In the lung there is at least a 30-fold increase in 

 arterial collateral circulation, whether or not the 

 veins are also ligated, 16 months after interruption of 

 the pulmonary artery (fig. 12), and there is evidence 

 still of a continuing rise at this late time, although 

 this is much less steep than in the first 2 months. In- 

 deed a highly pertinent question is what brings the 

 growth of these collateral vessels, or of any vessels, to 

 an end. 



