

THE HEART 43 



valves opening, so that for this brief period no blood is entering 

 the ventricles, which are screened off from all parts of the 

 circulatory system. This period is known as the postsphygmic. 

 Meanwhile the ventricular walls are relaxing, and as. the cavity 

 of the ventricle expands the pressure falls sufficiently to allow 

 the auriculo- ventricular valves to open, and blood pours in from 

 the auricle. 



This is now the period of heart pause, during which both 

 auricles and ventricles are filling simultaneously ; it is succeeded 

 by the contraction of the auricles, by which the ventricles are still 

 further distended, and under the steadily increasing pressure in 

 the ventricles the auriculo-ventricular valves are closed. This 

 point occurs in Fig. 18 shortly after the beginning of the up- 

 stroke on the ventricular curve. The closure of the auriculo- 

 ventricular valves is referred to as the third standard movement 

 The ventricles are now full of blood shut off from the auricles 

 by the auriculo-ventricular valves, and shut off from the general 

 circulation by the closed aortic and pulmonary valves. This 

 period, which is extremely brief, is known as the presphygmic, 

 the period of rising pressure, or, as Stewart graphically puts it, 

 the period during which the ventricles are ' getting up steam.' 

 No blood can leave the ventricles until the pressure in their 

 cavities rises above the aortic and pulmonary pressures. 

 With the opening of the semilunar valves the blood is leaving the 

 heart, and it continues to leave it during the period shown on 

 the tracing as the systolic plateau. 



If Fig. 18 be again referred to, and the curve given by the 

 auricles examined, three well-marked waves will be seen ; the 

 first and largest, known as 'A,' we have previously referred to 

 as corresponding with the contraction of the auricle ; the second 

 positive wave, known as ' C/ occurs during the rising pressure in 

 the ventricles, and is probably due to the bulging of the auriculo- 

 ventricular valves into the interior of the auricle. Chauveau, 

 with a finger in the contracting auricle of the horse, says this 

 upward bulging does occur. The cause of the third wave, known 

 as 'V,' is not yet agreed upon. The interest in these auricular 

 curves is mainly clinical ; similar waves may be observed in 

 veins near the heart, and the venous pulse thus obtained may be 

 employed to indicate irregularities in auricular contraction. We 

 shall see presently that the contraction of the heart is initiated 

 in the right auricle, so that a clinical examination of the behaviour 

 of this cavity through the medium of the jugular pulse is a 

 method of diagnosis of the utmost importance. In modern 

 investigations of heart irregularities the most valuable infor- 

 mation is being afforded by the A to C interval, or the time 

 distance between the waves representing auricular and ventricular 



