148 INFLUENCE OF RESPIRATORY MOVEMENTS ON PULSE-CURVE. 



into the left ventricle when the venti'icle relaxes; (3) not unfrequently a pro- 

 jection occurs at the apex, due to the elastic vibration of the tense arterial wall ; 

 (4) the dicrotic wave (R) is small compared with the size of the curve itself, 

 because the pulse-wave, owing to the lesion of the aortic valves, has not a suffi- 

 ciently large surface to be reflected from. The great height of the curve is 

 explained by the large amount of blood projected into the aortic system by the 

 greatly hypertrophied and dilated ventricle. 



74. Influence of the Respiratory Movements on 



the Pulse-Curve. 



The respiratory movements influence the pulse in two ways : (1) 

 in a purely physical way, by diminishing the arterial pressure during 

 each inspiration and increasing it during expiration; (2) the respir- 

 atory movements are accompanied by stimulation of the vasomotor 

 centre, which produces variation of the blood-pressure. 



(a.) Normal Respiration. During inspiration, owing to the dilatation 

 of the thorax, more arterial blood is retained within the chest, while at 

 the same time, venous blood is sucked into the right auricle by 

 aspiration; as a consequence of this, the tension in the arteries during 

 inspiration must be less. The diminution of the chest during expiration 

 favours the flow in the arteries, while it retards the flow of the venous 

 blood in the venae cavse two factors which raise the tension in the 

 arterial system. The difference of pressure explains the difference in 

 the form of the pulse-curve obtained during inspiration and expiration, 

 as in Fig. 63 and Fig. 58, I., III., IV., in which J indicates the part of 

 the curve which occurred during inspiration, and E the expiratory por- 

 tion. The following are the points of difference: (1.) The greater dis- 

 tension of the arteries during expiration causes all the parts of the 



Fig. 63. 



Influence of the respiration upon the sphygmogram, after Riegel J, during in- 

 spiration; E, during expiration. 



curve occurring during this phase to be higher; (2.) the line of 

 ascent is lengthened during expiration, because the expiratory thoracic 

 movement helps to increase the force of the expiratory wave; (3.) 



