368 THE MECHANICS OF THE CIRCULATION, HEMODYNAMICS 



The Method of Auscultation. The moment of the disappearance 

 and reappearance of the pulse may also be determined by means of 

 auscultation, because, as Marey has noted, the constriction of an artery 

 gives rise to noises (bruit de souffle) which are heard best distally to 

 and in the immediate vicinity of the constriction. Thus, if a stetho- 

 scope is applied over the brachial artery below the border of the arm- 

 piece, 1 the gradual deflation finally gives rise to a sharp blowing sound 

 which presently becomes fuller and then disappears altogether. The 

 first occurrence of this sound indicates the systolic height of the blood 

 pressure, while the moment at which the sound beco^mes muffled shortly 

 before its complete disappearance, corresponds to its diastolic value. 

 The mean pressure can only be obtained in an approximate way with 

 the help of these two extremes. 



The Graphic Method. The determination of the blood pressure 

 may also be attempted in accordance with the principle that the 

 arterial wall executes its greatest movements at 'a time when the 

 intravascular pressure is accurately balanced by the outside pressure. 

 This fact to which attention was first called by Marey, has been proven 

 experimentally by Mosso upon excised segments of arteries. The 

 idea is to oppose the intravascular pressure by an outside pressure 

 which, being equal to that within, permits the most perfect elastic 

 play of the arterial walls. Thus, if the hand is placed in a receptacle 

 filled with mercury, the pulse is felt either at the base of the thumb 

 or along the fingers. In accordance with von Frey, 2 the pressure 

 prevailing in the blood-vessels of the hand may be obtained by deter- 

 mining in millimeters the depth to which it must be pushed into the 

 mercury in order to produce this subjective phenomenon. In a simi- 

 lar way, it is possible to register the arterial pressure upon the paper 

 of a kymograph by simply connecting a recording tambour with the 

 cuff of a sphygmomanometer or with the free end of its mercurial in- 

 dicator. During the complete compression of the brachial artery, the 

 pulsations so registered retain a small amplitude, because they are 

 simply transmitted from the central end of this blood-vessel. When 

 however, the outside pressure is lowered step by step, their size is 

 gradually increased up to the time when the diastolic mean value of the 

 blood pressure has been reached. Subsequent to this point the con- 

 spicuousness of these oscillations is again diminished. In this way, 

 the moment may be accurately determined at which the outside or 

 extravascular pressure precisely equals the intravascular pressure. 

 Quite similarly, if the pressure is gradually increased, the beginning 

 of the large oscillations indicates the diastolic minimum. 



This procedure must be followed if measurements are undertaken 



1 In accordance with Janowski, Miinchener med. Wochenschr, 1907, the aus- 

 cultation method was first employed by Karotkow in 1895. Also see: Strass- 

 burger, D. Archiv fur klin. Med., 1907, 459, and Fellner, Verhandl., Kongr. ftir 

 inn. Med., 1907. 



2 Festschrift fur B. Schmidt, Leipzig, 1896, 79. 



