PATHOLOGICAL DISTURBANCES OF CARDIAC ACTION. 79 



(3.) Opening of the Semi-lunar Valves. When the pressure within 

 the ventricle exceeds that in the arteries, the semi-lunar valves are 

 forced open and stretched like a sail across the pocket-like sinus, 

 without, however, being firmly or directly applied to the wall of the 

 arteries (pulmonary and aorta), and thus the blood enters the arteries. 



Negative Pressure in the Ventricle. Goltz and Gaule found that there was 

 a negative pressure of 23 "5 mm. Hg. (dog) in the interior of the ventricle during a 

 certain phase of the heart's action. They surmised that that phase coincided with 

 the diastolic dilatation, for which they assumed a considerable power of aspiration. 

 Marey observed a similar condition and called it " vacuite postsystolique," but 

 thought that it coincided with the end of the systole; while Moens is of opinion that 

 this negative pressure within the ventricle obtains shortly lie/ore the. systole has 

 reached its height, i.e., just before the inner surface of the ventricles and the 

 valves, after the blood is expelled, are nearly in apposition. He explains this 

 aspiration as being due to the formation of an empty space in the ventricle caused 

 by the energetic expulsion of the blood through the aorta and pulmonary artery. 



(D.) Pause. As soon as the ventricular contraction ends, and the 

 ventricles begin to relax, the semi-lunar valves close. The diastole of 

 the ventricles is followed by the PAUSE. Under normal circumstances 

 the right and left halves of the heart always contract or relax uni- 

 formly and simultaneously. 



49. Pathological Disturbances of Cardiac Action. 



Cardiac Hypertrophy. All RESISTANCES to the movement of the blood 

 through the various compartments of the heart, and through the vessels com- 

 municating with it, cause a greater amount of work to be thrown upon the 

 portion of the heart specially related to this part of the circulatory system ; con- 

 sequently, there is produced an increase in the thickness of the muscular walls 

 and dilatation of the heart. If the resistance or obstacle does not act upon 

 one part of the heart alone, but on parts lying in the onward direction of the 

 blood-stream, these parts also subsequently undergo hypertrophy. If in addi- 

 tion to the muscular thickening of a part of the heart the cavity is simultaneously 

 dilated, it is spoken of as eccentric hypertrophy or hypertrophy with dilatation. 



The obstacles most likely to occur in the blood-vessels are narrowing of the 

 lumen or want of elasticity in their walls ; in the heart, narrowing of the arterial 

 or venous orifices or insufficiency or incompeteucy of the valves. Incompetency 

 of the valves forms an obstruction to the movement of the blood, by allowing 

 part of the blood to flow back or regurgitate, thus throwing extra work upon 

 the heart. 



Thus arise (1.) Hypertrophy of the left ventricle, owing to resistance in the area 

 of the systemic circulation, especially in the arteries and capillaries not in the 

 veins. Amongst the causes are, constriction of the orifice or other parts of the 

 aorta, calcification, atheroma, and want of elasticity of the large arteries and 

 irregular dilatations in their course (Aneurisms) ; insufficiency of the aortic 

 valves, in which case the same pressure always obtain within the ventricle and in 

 the aorta ; and lastly, contraction of the kidneys, so that the excretion of water by 

 these organs is diminished. Even in mitral insufficiency compensatory hyper- 

 trophy of the left ventricle must occur, owing to the hypertrophy of the left atrium 

 in consequence of the increased blood-pressure in the pulmonary circuit. 



