THE CIRCULATION OF THE BLOOD. 279 



the jugular vein or into the left ventricle through the carotid artery. Both 

 cannula and tambour are filled with an alkaline solution to prevent coagula- 

 tion of the blood, and then made air-tight. The pressure of the blood in the 

 ventricle is thus transmitted by a liquid column to the tambour and to its 

 attached lever. With such a manometer a curve is registered similar to that 

 shown in Fig. 128. To obtain the absolute value of this curve in millimeters 

 of mercury it is necessary to graduate the instrument previously. An 

 examination of the curve shows that previous to the ventricular contraction 

 there is a very slight rise of pressure above that of the atmosphere, repre- 

 sented by the line a b. This may be due to the inflow of blood from the 

 auricle during the diastole. At o the pressure suddenly rises, passes quickly 

 to its maximum value, (2), which is maintained with slight variations for 

 some time, and then suddenly (3) begins to fall, and rapidly reaches the 

 line of atmospheric pressure, or even passes below it, becoming negative in 

 fact for a short period. The curve may also be taken as a record of the 

 ventricular contraction, for there are reasons to believe that the two closely 

 coincide throughout their entire course. A characteristic feature of this 

 curve is the more or less horizontal portion comprised between the points 

 2 and 3, marked by several elevations and depressions, which has been 

 termed the systolic plateau. 



With other forms of elastic manometers, especially those in which the 

 transmission of the intra-ventricular pressure is effected by air or by a com- 

 bination of air and liquid, this portion of the curve is represented by a single 

 peak, which is taken as an indication that the maximal pressure once reached 

 is not maintained, but immediately begins to fall to its original level, not- 

 withstanding the continued contraction of the ventricle. Those who adhere 

 to this view attribute the plateau to the closure of the orifice of the catheter 

 by the contracting and approximating walls of the ventricle. There are 

 reasons for believing, however, that the former curve is the more correct repre- 

 sentation of the course of the intra-ventricular pressure. Bayliss and Star- 

 ling photographed on a moving surface the oscillations of a fluid, a solution 

 of sodium sulphate, in a capillary glass tube one end of which was closed, 

 the other end placed in connection with an intra-cardiac catheter, the oscil- 

 lations representing the variations in pressure. The photogram thus 

 obtained resembles the curve obtained by Hlirthle's membrane manometer. 



The Relation of the Intra-ventricular Pressure Curve to the Intra- 

 cardiac Mechanisms. By itself the curve of the intra-ventricular pressure 

 affords no indication as to events occurring within the heart: i.e., as to the 

 times during the systole, of the closure of the auriculo- ventricular valves and 

 the opening of the semilunar valves, or the times during the diastole, of the 

 closure of the semilunar valves and the opening of the auriculo-ventricular 

 valves. 



By registering the curve of pressure in the aorta simultaneously with the 

 pressure in the left ventricle (Fig. 128), and by comparing these with the 

 curve of the successive differences of pressure in these two cavities as deter- 

 mined by the "differential manometer," it becomes possible to mark on the 

 ventricular pressure curve the points at which the foregoing events take 

 place. As the outcome of many observations and determinations, the 

 following statements may be made: As a point of departure for a considera- 



