194 



PHYSIOLOGY 



CHAP. 



The synchronous contraction of the ventriculo- valvular fibres 

 augments their expulsive efficiency. 



In this complex theory of the mechanism of the auriculo- 

 ventricular valves (which we have insisted on for thirty years), 

 the fact which is usually less generally accepted is that of 

 the presystolic closure of the venous orifices, which we hold to 

 be an indispensable condition of the normal exclusion from the 

 systole of all trace of reflux from ventricles to auricles. Chauveau, 

 while maintaining the theory of Klirschner, says expressly that 

 " les valvules auriculo-ventriculaires sont pendantes a la fin de la 

 systole auriculaire " (1876) ; without considering that if this pheno- 

 menon (which in his experiments is obviously the result of 

 weakened functions in the exposed heart of the horse, injured, 



moreover, by the introduction of the 

 finger into the auricle) were normal, 

 there would, under physiological 

 conditions, be a pronounced reflux 

 of blood into the auricle at the be- 

 ginning of systole, synchronously 

 with the sharp rise of the valves. 

 For it is clear that at systole the 

 pressure increases not only in the 

 blood that is beneath the valves, but 

 also in that which lies along the axis 

 of the ostium, and which can flow 

 back freely so long as the valves are 

 not closed. 



The mechanism of valvular 

 closure at the systolic dead point 



ig demonstrated 1)V the following 

 . , -11 



experiment upon the excised heart 

 of man, pig, or other large mammal. 

 The cardiac cavity must be washed free of clot, and corks 

 fixed in the aorta and pulmonary artery, which are cut off short ; 

 the two auricular cavities are then opened freely from above, 

 and the margins of the openings attached to an iron ring upon 

 a support (Fig. 60) without tearing or deforming the base of 

 the ventricles. When the valves are normal, and rigor mortis 

 has passed off, it is only necessary to fill the two ventricles and 

 the funnel-shaped cavity formed by the walls of the auricles 

 with water, in order to see how the valves float up and assume 

 the half-open position. If presystole be now imitated, by 

 injecting a few c.c. of water with a powerful syringe, the nozzle 

 of which is directed towards the centre of the (right or left) 

 auriculo-ventricular ostiuui, a marked rise of the valvular flaps 

 will be seen, with such approximation of the borders that the 

 orifice is converted into a narrow slit, in consequence of the 



FIG. 5 P.-Diagram showing position of 



auriculo-ventricular flaps of valves at 

 commencement of systole, owing to 



of chordae tendmae. (Krehi.) 



