366 THE MECHANICS OF THE CIRCULATION, HEMODYNAMICS 



Radial artery at wrist 150-160 mm. Hg 



Radial artery at base of thumb 120-130 mm. Hg 



Radial artery at last phalanx 100-110 mm. Hg 



In this connection the following determinations of the mean blood 

 pressure in dogs, made by Dawson, ^ may be of interest: 



Carotid, brachocephalic, superior mesenteric and renal 



arteries 123 mm. Hg 



Inferior mesenteric artery 119 mm. Hg 



Iliac, femoral, saphenous and brachial arteries 118 mm. Hg 



Arteries of the circle of Willis 104 mm. Hg 



The Indirect Method of Recording the Arterial Blood Pressure. 



The Method of Palpation. — The principle upon which the indirect 



method is based is simple, and has really 



r /^^ — ^^'^^'^^ been employed for centuries in palpating 



^^'^ 7^ ^xS. ^^^ pulse. Two or three fingers are usually 



used for this purpose, the artery being com- 



W*'^'*^^ \l pressed with the central finger until the 



naff I JtB 1 1 pulsations can no longer be felt with the 



^'^*^==^^CI/^ lii ^ore distal one. The force required to 



occlude the artery serves as the measure 



of the pressure existing within it. 



The indirect method consists in estab- 

 lishing a known outside pressure which ex- 

 ^Sphygmo'^TSL^S!'' actly balances the pressure in the blood- 



C, metal capsule and rubber vessel. The first mstrument of this type 

 pouch for occluding artery; M, was Constructed by Vierordt^ who attempted 

 tonometer for registration of ^^ measure the degree of pressure neces- 



pressure which is necessary to , ,. ° ^ . , . 



occlude the artery. sary to obliterate an artery by attaching 



a pelotte to the receiving lever of a sphygmo- 

 graph. A distinct advance was made in 1876 by v. Basch^ who employed 

 a glass tube which was closed at one end by a rubber membrane and 

 was then filled with water. Its free end was joined with a mercury 

 manometer so that the pressure required to occlude the artery could 

 be accurately registered. In 1883, v. Basch advised the use of a metal 

 capsule (C) which was closed by a rubber membrane and equipped with 

 a metal spring and indicator {M). This principle was subsequently 

 made use of in the construction of the dynamometer of Hill and 

 Bernard^ and the sphygmometer of Oliver.^ At about this time the 

 experiments of Marey led to the invention of the plethysmograph, an 

 instrument which was made use of by him as well as by Hiirthle® and 

 Mosso^ for the compression of the artery. 



1 Am. Jour, of Physiol., xv, 1905, 244. 



2 Lehre vom Arterienpuls, 1855. 



3 Zeitschr. flir klin. Med., ii, 1883, 79. 

 ^ Jour, of Physiol., xxiii, 1898, 4. 



5 Ibid., xxii, 1897, 51. 



^ Deutsche med. Wochenschr., 1896. 



7 Zentralbl. flir Physiol., x, 1896. 



