6 4 



CAUSE OF THE CARDIAC IMPULSE. 



blood is discharged into the aorta and pulmonary artery, whereby the apex goes in 

 the opposite direction, i.e., downwards and slightly outwards. Landois however 

 has shown that the mass of blood is discharged into the vessels 0'08 of a second 

 after the beginning of the systole, while the cardiac impulse occurs with the first 



(5) When the blood is discharged into the aorta and pulmonary artery, these 

 vessels are slightly elongated, owing to the increased blood-pressure. As the heart 

 }s suspended from above by these vessels, 

 the apex is pressed slightly downwards and 

 forwards towards the intercostal space (1). 



As the cardiac impulse is observed in the empty 

 hearts of dead animals, (4) and (5) are certainly 

 of only second-rate importance. Filehne and 

 Pentzoldt maintain that the apex during systole 

 does not move to the left and downwards, as must 



Fig. 40. 

 I. Schematic horizontal section through the heart, lungs, and thorax, to show the change of 

 shape which the base of* the heart undergoes during contraction of the ventricle F, G, 

 transverse diameter of the ventricle during diastole ; c, position of the thoracic wall ; a, b, 

 transverse diameter of the heart during systole, with e, position of the anterior thoracic 

 wall during systole. II. Side-view of the heart i, apex during diastole ; p y during 

 systole. 



be the case in (4) and (5), but that it moves upward and to the right a result corroborated by 

 v. Ziemssen. [Barr attributes the cause of the impulse to the rigidity or hardening of the ven- 

 tricle during systole, to the rotatory movement and lengthening downwards of the blood- 

 column in the aorta and pulmonary artery, while towards the end of the systole the maximum 

 of recoil takes place and also contributes to cause it.] 



It is to be remembered that as the apex is always applied to the chest-wall, separated from it 

 merely by the thin margin of the lung, it only presses against the intercostal space during 

 systole (Kiwisch). 



After the apex of the curve, c, has been reached at the end of the systole, the 

 curve falls rapidly, as the ventricles quickly become relaxed. In the descending 

 part of the curve, at d and e, are two elevations, which occur simultaneously 

 with the second sound. These are caused by the sudden closure of the semi-lunar 

 valves, whereby an impulse is propagated through the axis of the ventricle to its 

 apex, and thus causes a vibration of the intercostal space ; d corresponds to the 

 closure of the aortic valves, and e to the closure of the pulmonary valves. The 

 closure of the valves in these two vessels is not simultaneous, but is separated by 

 an interval of 0*05 to 0*09 sec. The aortic valves close sooner on account of the 



