282 TEXT-BOOK OF PHYSIOLOGY. 



nected by its free extremity with a Hiirthle tambour. The curve of pressure 

 thus obtained, shown in Fig. 129,* is characterized by three positive and three 

 negative waves. Among the more important of the indirect determinations 

 of the auricular pressure variations are those of Bachmann, carried out with 

 highly sensitive recording tambours. The curve of pressure variations in 

 the jugular vein thus obtained, by Bachmann, Fig. 130, is placed in juxta- 

 position for purposes of comparison. 



The first positive wave, a, is caused by the systole of the auricle and 

 amounts to about 9 millimeters of mercury. The first negative wave is due 

 to the relaxation of the auricle. 



V 



\J if 



af 



FIG. 129. CURVE OF PRESSURE VARIATIONS FIG. 130. CURVE OF PRESSURE VARIATIONS IN 

 IN THE AURICLE. (Enlarged). (Porter.} THE JUGULAR VEIN. (Enlarged.) (Bachmann.} 



The second positive wave, 2 s, is not of auricular origin, but is due to 

 the systole of the ventricle in its early stage corresponding to the period 

 between the closure of the auriculo-ventricular valve, and the opening of 

 the semilunar valves, the period of rising tension, and amounts to about 

 5 mm. of Hg. It is probably due to the bulging of the auriculo-ventricular 

 valve into the auricular cavity, by the still higher ventricular pressure, thus 

 diminishing its size and raising the pressure. 



The second negative wave, a/, begins with the opening of the semi- 

 lunar valves, determined by comparison with a simultaneously recorded 

 curve of intra-ventricular pressure, and is due in part to the relaxation of 

 the auricular walls, but more especially to a descent of the more central 

 portions of the auriculo-ventricular septum, into the ventricular cavity, 

 due to the contraction of the papillary muscles during the ventricular 

 systole. The hollow cone thus formed enlarges the auricular cavity, 

 withdraws some of its contained blood, and hence lowers the pressure, 

 thus contributing materially to the filling of the auricle. This negative 

 pressure amounts to about 10 mm. of Hg. 



The third positive wave, v, occurs toward the end of the ventricular 

 systole and is probably caused by an inflow of blood from the veins as 



4f.f l The original tracing obtained by Porter is shown in the ac- 



companying Fig. 131. The letters designating the waves have 

 *. tne following significance. A, systolic rise; AB, first diastolic 



A \, J, fall; BC, first diastolic rise; CD, second diastolic fall; E, second 



diastolic rise; F, third diastolic fall; G, pause. In Fig. 129 

 the tracing has been enlarged and the waves relettered and named 

 m * accordance with the terminology in vogue in the literature of 



Chnical medlcme ' 



*The corresponding wave on the curve of the pressure variations in the jugular vein is 

 believed by Mackenzie to be due to the impact of the expanding carotid artery, and hence calls it 

 the carotid, c, wave; inasmuch as it occurs in point of time with the beginning of the ventric- 

 ular systole, it is also called the systolic, s, wave. 



