Resistance to Compression of the Arterial Wall. 157 



Twenty carotids from adults. 



Internal pressure = 100 mm. Hg. Difference of 

 pressure at which flow: 



Number examined. Condition. Ceased. Returned. 



16 Slight Maximum 30 19 



atheroma. Average 15 9 



Minimum 3 o 



3 Moderate Maximum 13 9 



atheroma. Average 10 5 



Minimum 6 2 



1 Calcified. 28 14 



These observations show clearly that, other things being equal, 

 small arteries with thin walls are more readily compressed than 

 large arteries with thick walls, but in no case was a higher pressure 

 than 19 millimeters required. 



Some experiments were made on the passage of a wave, showing 

 that at the point of return of the flow a small pulse wave was 

 transmitted through the artery. 



Arteries from amputated limbs were examined in the hope 

 that they might be obtained in a surviving state and that the 

 effects of tonus upon the compressibility might be studied. 

 Though examined within two hours after removal we were unable 

 to demonstrate clearly their surviving character, so that our re- 

 sults with them must be considered merely corroborative of those 

 with dead vessels. 



Difference of pressure at which flow: 

 Artery. Length. Ceased. Returned. 



Normal femoral 7.5 cm. 4 3 



Normal femoral 7 " 11 2 



Calcified post tibial 11 " 24 11 



Extremely calcified femoral 8 " 28 16 



These results, with the single calcified post-mortem vessel, 

 show that the effect of even extreme calcification of the vessel is 

 not very great, n to 16 millimeters being the over pressure found 

 requisite for these vessels, which is less than the resistance found 

 in some practically normal vessels. The evidence is, therefore, 

 clear that other factors are of preponderating importance. 



Since the study of O. B. Meyer demonstrated the extreme 

 degree of contraction into which ox carotids pass when placed in 

 ice cold Ringer's solution, and that such arteries, warmed and 

 stretched to overcome this contraction, react to vaso-constrictor 



