THE AURICULO- VENTRICULAR VALVES. 



1 1 



levers. The first two observers found that the contraction of the 

 papillary muscles occurred very shortly after that of the ventricular 

 wall ; by Haycraft and Paterson the contraction in vigorous hearts was 

 found to be synchronous with that of the ventricular wall, while it 

 subsequently became later when the rhythm of the heart began to 

 fail. 



Roy and Adami's method is not free from fallacy. The movements of 

 the hook and lever connected with the valve cannot correspond exactly to the 

 contraction and relaxation of the papillary muscles. For until the pull of 

 these muscles on the auriculo- ventricular valve becomes of such a strength that 

 it surpasses the difference in pressure between the auricle and ventricle, the 

 flaps will not move in either direction. Eoy and Adami found that the first 

 effect of the contraction of the ventricle is to push the valvular diaphragm 

 towards the auricle. The reverse movement does not necessarily mark the 

 beginning of the contraction of the papillary muscles, but marks the moment 

 when the pull of these muscles becomes greater than the intraventricular 

 pressure. Likewise, the fall of Roy and Adami's curve does not mark the end 

 of the contraction of the papillary muscles, but the time when the intra- 

 ventricular pressure has become higher than the tension exerted by those 

 muscles. The variations, then, in Roy and Adami's curves must be referred 

 not only to the contraction of the papillary muscles, but also to the changes in 

 intracardiac pressure. 



The most reasonable view to hold is that the papillary muscles 

 contract synchronously with the ventricular wall, for the rate of 

 propagation of the contraction wave in the heart is so fast, reaching 

 5 metres a second or more, that, for all practical purposes, we may 

 say that the contraction of the whole ventricle is synchronous. Thus, 

 in the rabbit's heart, beating 180 times in a minute, each complete 

 cardiac cycle occupies \ second. The ventricular systole occupies about 

 \ of that time, that is \ second. The length of the ventricle is some 

 20 mm., the rate of propagation of the contraction wave can be taken as 

 5000 mm. a second. The whole ventricle would therefore have passed 

 into systole in T i F second, while it continues in systole for \ second. 

 Considering that the papillary muscles are in direct continuity with 

 the general musculature of the heart, it is difficult to conceive how the 

 wave of contractility could be delayed from reaching these muscles, 

 even for so long as ^ru second in the rabbit. The records of the action 

 current of the heart, obtained with the capillary electrometer, suggest 

 no such delay as is found by Roy and Adami. 



It has been stated that the mitral valve closes much more perfectly 

 than the tricuspid valve, and that, therefore, considerable regurgitation can 

 take place through the latter when the right heart is over-distended. 1 



The normal heart must be greatly distended before actual regurgita- 

 tion takes place past any of the valves. The perfect structure of the valves 

 effectually prevents this. A back effect, causing a congestion of the blood 

 in the venous system, can be brought about quite simply and without tin- 

 aid of systolic regurgitation. The heart fails to empty its cavities at each 

 systole, and thus the diastolic pressure is increased at a time when the 

 valves are naturally open. The blood does not regurgitate during systole, 

 but at each diastole the veins are unable to empty their full quota of 

 blood into the ventricle, for the ventricular cavity is already partially filled. 

 On asphyxiating a curarised animal, regurgitation from the right ventricle is 



1 Flint, "Physiology," 1866, p. 201. 



