POWER AND WORK OF THE HEART 177 



Furthermore,, the heart in its own systole exercises a favorable influence 

 on the return flow of the blood. During systole the volume of the ventricles 

 is diminished by exactly the volume of the blood driven out. This blood is 

 partly taken up by the intrathoracic arteries and the pulmonary vessels, but 

 part of it leaves the thorax. The consequence is that the content of the 

 thorax is smaller. This in its turn produces a suction in the thoracic cavity 

 which acts either to draw air into the lungs through the open glottis (cardio- 

 pneumatic movement), or to produce a sinking of the chest wall, or finally 

 to expand the intrathoracic veins whereby blood is drawn into them. 



Finally, it has been demonstrated that the heart exercises a suction on the 

 blood in passing into diastole. By means of a minimum valve Goltz and 

 Gaule and others have observed in the open thorax of a dog a negative pressure 

 of 100-320 mm. of water in the left ventricle, 1025 mm. of water in the 

 right ventricle. Under the same circumstances (open thorax) a negative 

 pressure can be demonstrated in the auricles (De Jager et aL). 



One succeeds however in demonstrating such a suction only with a vigor- 

 ously active heart. If the heart movement is weak and if the heart does not 

 empty itself well when it contracts, the suction effect is considerably diminished. 

 What the forces are which bring about this suction is not fully explained. 



Excessive filling of the left ventricle is prevented by its thick wall. In 

 the right ventricle the wall is too thin to present sufficient resistance against 

 a very powerful flow of blood, but the danger of overdistention is prevented 

 in part at least by the fact that muscular cords are stretched across the cavity 

 of the right ventricle at different levels. ~. 



Moreover the pericardium plays an important role, as appears from the fol- 

 lowing among other observations : a cat's heart held 12 cc. when the pericardium 

 was uninjured, when the pericardium was punctured 11 cc. more could still be 

 driven into the heart (chiefly the right auricle and right ventricle) with the 

 same pressure. Even when beating normally the heart during diastole protrudes 

 through a slit made in the pericardium. Finally it should be remarked that a 

 relative insufficiency in the right atrio-ventricular valve appears after opening 

 of the pericardium. The closure of this valve is insured by the support which 

 the pericardium affords to the heart (Barnard). 



8. POWER AND WORK OF THE HEART 

 A. POWER 



We have already seen that the left ventricle in its systole may exert a 

 pressure of 200 mm. Hg. and more on the blood. A weight of this size might 

 then be said to press upon the inner wall of the ventricle. Nevertheless it is 

 able to contract, and its power must be everywhere sufficient to balance such a 

 maximal pressure. In other words, the power of every square centimeter of 

 the internal surface of the left ventricle is equal to the weight of a column 

 of Hg. 1 sq. cm. in section and as high as the maximal pressure expressed 

 in terms of Hg. If we assume that the maximal pressure amounts to 200 

 mm. Hg., the power of the left ventricle for every square centimeter of its 



