CHARACTERISTICS OF THE RADIAL PULSE CURVE. 107 



At the moment of the deep inspiration, not only are the peripheral veins 

 emptied into the thorax, but the blood in the peripheral arteries is also sucked 

 back into the thoracic aorta. Thus the tension in the radial vessels falls 

 below zero ; in fact, the systemic circulation entirely ceases until the left 

 ventricle once more becomes filled with blood from the pulmonary veins. 

 These experiments are performed with far greater effect by a man with a 

 compressible than with a rigid thorax. 



The sphygmogram shows variations synchronous with the respiratory 

 movements. Normally these are slight, but they become marked when- 

 ever the respiration is either deep or partially obstructed. During deep 

 inspiration the line of the tracing falls, whilst the excursion of 

 the primary wave decreases, and the dicrotic wave becomes more 

 evident. The veme comites radiales are here emptied, and the expanded 

 lungs swallow up the blood so that the arterial tension falls slightly. 

 When expiration follows, the line of the tracing rises, and the excursion 

 of each pulse is increased. During a deep inspiration the vessels in the 

 radial sulcus appear to the finger of less breadth and lower tension. 

 In obstructed breathing the pulse beats may, during inspiration, almost 

 disappear, for the air cannot then enter freely, and thus the force of 

 the inspiratory movement is thrown largely on to the intra-thoracic 

 vessels and the heart. 



Passive compression of the thorax produces the same effect on the 

 pulse as Valsalva's experiment, if the breath be held (Fig. 71, tracing 

 4). If, on the other hand, the breath be allowed to escape as the thorax 

 is compressed, the line of the tracing falls, and the pulse beats become 

 abortive (Fig. 71, tracing 5). In this latter condition the outlet of the 

 peripheral veins is not blocked, while the beat of the heart is mechanic- 

 ally opposed by the compression. 



So soon as the fact is once grasped that the veins which surround 

 the radial artery bear an important share in the production of the 

 phenomena of the pulse, almost all the difficulties which have hitherto 

 surrounded the explanation of sphygmographic tracings under these 

 conditions disap- 

 pear. In place of 

 these, an absolute 

 agreement between 

 the results ol >tained 

 on animals by man- 

 ometric observa- 

 tions, and those re- 

 corded on man with 

 the sphygmograph, 

 becomes apparent. 



In all patholog- 

 ical conditions of 

 obstruction of the 

 circulation, arising from pulmonary or cardiac disease, wherein by back 

 pressure the general venous tension is raised, and the arterial tension 

 lowered, the veins which surround the artery must have an important share 

 in giving to the pulse the quality of breadth or fulness which is so com- 

 monly combined with that of low tension. When the quality of fulness 

 is estimated to be present between the pulse beats, this does not betoken 

 a high arterial tension, but rather an engorgement of the venous system. 



TRACING 2 



Fig. 72. — Two examples of the effect of occluding the brachial 

 artery. A, Artery compressed ; B, compression withdrawn. — 

 Hill, Barnard, and Sequeira. 



