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A MANUAL OF VETERINARY PHYSIOLOGY 



along the surface of the blood-stream ; the blood-current runs, 

 as it were, within the pulse-wave ; the former travels at a high 

 speed, the latter comparatively slowly, at most some 381 mm. 

 (15 inches) per second. The case is similar to that of a 

 wave seen moving rapidly over the surface of a slowly flowing 

 stream. 



The pulse-wave can be studied by means of the graphic 

 method ; it is obvious that a lever placed on a pulsating vessel 

 will be moved up and down, and may be made to trace a curve 

 which will record the passage of the pulse- wave under the lever 

 at that particular spot. A tracing thus obtained, known as a 

 sphygmogram, simply registers the expansion 'and recoil of the 

 artery while the wave is passing ; it will not give a tracing of 

 the pulse-wave itself, which, as we have seen, is 18 feet in length, 

 but it gives the details of the form of the wave. But it may 

 be at once said that unless the proper degree of pressure is kept 



Fig. 30. — Normal Sphygmogram modified from Dudgeon ; Pressure 

 2 Ounces "(Hamilton). 



v.e, The period of ventricular systole ; v.d, the period of ventricular diastole ; 

 r, the period of rest ; a, b, c, primary or percussion wave ; d, first tidal or 

 predicrotic wave ; e, aortic notch ; /, dicrotic wave ; g, second tidal wave. 



on the vessel, great irregularity in the sphygmograms will be 

 produced, due to instrumental errors, and not to the true pulse- 

 wave. 



The simplest description of a sphygmogram (Fig. 30) is that it 

 consists of a nearly vertical unbroken upstroke (the anacrotic 

 limb), and an oblique downstroke (the catacrotic limb), which is 

 broken by two or three waves known as catacrotic waves. Of 

 these two or three waves / (Fig. 30) is one of the few which 

 occurs with any regularity, and is known as the dicrotic wave. 

 The notch e is described as the aortic notch, and is caused by 

 the closure of the aortic valves. The dicrotic wave is produced 

 by a recoil of blood, the result of closure of the aortic valves ; this 

 reflected wave passes from the centre over the whole arterial 

 system. The smaller waves in the catacrotic limb are either 

 vibrations of the arterial wall, or reflections of the pulse-wave 

 from the periphery towards the heart. That the dicrotic wave 



