134 



326 J. A. MACWILLIAM 



Pressures in aortic regurgitation. Since the remarkable arm-leg 

 systolic pressure difference was recognised in cases of aortic regurgita- 

 tion by Hill, Flack and Holtzman (64) in 1909, numerous observations 

 have been made and differences of varying degrees of magnitude have 

 been recorded, one of 200 mm. by Rolleston (114) — leg pressure 350, 

 arm 150 — while the differences have as a rule been much smaller. 

 Similar phenomena have been observed in some other conditions — 

 violent muscular exertion in healthy persons, some cases with arterial 

 sclerosis, and in exophthalmic goitre. In these conditions question 

 naturally arises as to which reading represents the "blood-pressure." 

 The mechanism involved has proved difficult of elucidation. L. Hill 

 suggested a different "conductance" in the leg arteries, transmitting 

 the large systolic wave more effectively than in the arm. As the 

 diastolic pressure is virtually if not absolutely similar in arm and leg 

 it is evident that the systolic difference is a phenomenon of wave motion. 



There are indications that both a, cardiac and b, vascular conditions 

 are usually concerned in the mechanism of the arm-leg difference in 

 pressure. That a cardiac factor plays a part is suggested by the clinical 

 evidence to the effect that in man the differential pressure is slight or 

 absent in recent aortic lesions, and is chiefly found in cases of com- 

 pensated aortic regurgitation with their enlarged heart, large and 

 powerful systolic wave and unusually extensive pulse pressure— con- 

 ditions also present in greater or less degree in other instances where 

 the arm-leg difference has also been recorded, e.g., exophthalmic 

 goitre, some arterio-sclerotic cases, violent muscular exertion, etc. 



In toxic exophthalmic goitre many of the circulatory conditions 

 resembling those associated with aortic regurgitation (large heart, 

 exaggerated pulse pressure, etc.) may be strikingly present. Taussig 

 (123) has observed an arm-leg difference of 37 mm. Hg; the condition 

 has also been described by Harris (59). In a case of arterio-venous 

 aneurysm Lewis and Drury (83) have found that many similar circu- 

 latory features were temporarily abolished during artificial closure of 

 the arterio-venous communication, but not the differential pressure, 

 which they attribute to vascular conditions which had become estab- 

 lished. 



As regards experimental animals there is a conflict of evidence be- 

 tween the results of Bazett who described the immediate appearance 

 of a differential pressure after an aortic valve lesion, and those of 

 Leschke (84) who did not find a differential pressure at this stage. 



The important investigation recently published by Bazett (13) 



