3I g TEXT-BOOK OF PHYSIOLOGY. 



The Velocity of Propagation of the Pulse-wave. The propa- 

 gation of the pulse- wave from its origin at the root of the aorta to any 

 given point of the arterial system occupies an appreciable period of 

 time. The difference in time between the systole and the appearance 

 of the pulse- wave at the dorsal artery of the foot can be appreciated 

 by the sense of touch. The absolute time occupied by the wave in 

 reaching this point was determined by Czermak to be 0.193 second. 

 The rate at which the wave is propagated over the vessels of the lower 

 extremity has been estimated by the same observer at 11.16 meters 

 per second, and for the upper extremities at but 6.7 meters per second. 

 Other experimenters have obtained for the lower extremities some- 

 what different results, varying from 6.5 to n meters per second. 

 Weber's original estimate was from 7.92 to 9.24 meters per second. 

 The slower rate of movement in the vessels of the upper extremities 

 has been attributed to a greater distensibility of their walls, a condi- 

 tion unfavorable to rapid propagation. For this reason a low arterial 

 tension will occasion a delay in the appearance of the pulse-wave in 

 any portion of the body ; a high arterial tension will of course have the 

 opposite effect. The difference in the speed of the pulse-wave and 

 the blood-current shows that they are not identical and must not be 

 confounded with each other. 



The Sphygmograph. The alternate expansion and recoil of an 

 artery caused by the temporary increase and decrease of pressure 

 following each heart-beat can be graphically recorded on a traveling 

 surface by means of a special apparatus, the Sphygmograph or pulse- 

 writer. The tracing obtained in the form of a curve is termed the 

 pulse-curve or the sphygmogram. Different forms of this apparatus 

 have been devised by Marey, Dudgeon, v. Frey, and many others. 

 The instrument of v. Frey is shown in Fig. 151. This consists first of 

 a metal framework by which the apparatus is fastened to the arm and 

 support given to the lever, recording surface, etc. The essential part 

 is the spring carrying a button which is placed over the artery, usually 

 the radial, before it crosses the wrist- joint. A vertical rod transmits 

 the movement of the spring to the recording lever; the movements 

 of the latter are recorded on a small cylinder inclined slightly so that 

 the upstroke may be vertical. A small electro-magnet serves to 

 record the time. An average tracing taken from the radial artery is 

 shown in Fig. 152. This, however, is not a tracing of the pulse- wave, 

 but rather a record of the changes in pressure, their succession and 

 time relations, which follow each beat of the heart. The artery, 

 usually Delected for obtaining a sphygmogram is the radial. i*!ii3 

 artery lies quite superficially, covered only by connective tissue and 

 skin and supported by the flat surface of the radial bone, conditions 

 most favorable to technical investigation. 



The sphygmogram or pulse-curve may be divided into two portions : 



