4 8 THE MECHANISM OF THE CIRCULATION. 



The Systolic Output of the Heart and the Arterial Pressure. 



The determination of the exact output of the heart has been a 

 matter of considerable difficulty. In the calculation of the energy of the 

 circulation, it is shown that the output can be arrived at approximately 

 by hydrodynamic formulae, if certain data are obtained experimentally. 

 To arrive at one of these data, namely, the velocity of flow in the 

 ascending aorta, has always been a formidable matter. 



Volkmann 1 and Vierordt 2 estimated the velocity of the blood-flow 

 in the carotid artery, and, by comparing the sectional area of this with 

 that of the aorta, reckoned the velocity of flow in the aorta, and thus 

 the output of the heart per second. Now, the flow in such a tube as 

 the carotid depends at any moment on the proportionate relation which 

 obtains between the resistances in the carotid vascular area and in 

 the remainder of the arterial system. It is therefore impossible, from the 

 velocity of flow in the carotid artery, to accurately reckon the velocity 

 of flow in the aorta. It is equally impossible to determine the diastolic 

 capacity of the ventricle in the dead animal — not only because of the 

 fallacies which arise from the inadequacy of any method to imitate the 

 conditions of the living heart, but from the fact that the ventricle does 

 not completely empty itself during systole. 



Stolnikow 3 attempted to measure the output in a different manner. 

 He tied all the aortic branches except the axillary, and the outflow from 

 that artery he drew off into a graduated vessel. Prom thence the blood 

 was sent back to the heart by way of the external jugular vein. Under 

 these conditions, with a low resistance to flow, with the arterial pressure 

 rising to 30 or 40 mm. Hg only, and with ample filling of the heart in 

 diastole, the systolic output was probably maximal. He found it from 

 •00032 to - 0016 of the body weight. Tigerstedt 4 attacked the problem 

 directly, and, by means of an improved form of stromuhr, measured the 

 flow in the aorta of the rabbit. In fourteen experiments, wherein the 

 blood pressure averaged 88 - 5 to 176 mm. Hg, and the heart frequency 

 193, the mean outflow was '00027 of the body weight, and the 

 output per sec. -00085 of the body weight. Other observers have 

 availed themselves of indirect methods of arriving at the same result. 

 Thus Zuntz 5 estimated the blood-gases in arterial and venous blood, 

 and the gases of the expired air. He found that a resting horse 

 consumed 2733 c.c. of oxygen per minute, while the arterial blood 

 contained 10"33 per cent, more oxygen than venous blood. It follows 

 from these data that every 100 c.c. of blood which traversed the 

 lungs took up 10 - 33 per cent, of oxygen ; but, as in one minute 

 2733 c.c. of oxygen was carried away by the blood passing through 



the lungs, therefore ______ — 26,457 c.c. of blood must have 



10'33 



passed in the given time. This, then, was the output per minute of the 



right ventricle. The output per second was "00122 of the body weight 



(this was about 360 kilos.). By a similar investigation, the output per 



1 "Die Hiimodynanrik," Leipzig, 1850, S. 204. 



2 " Die Erscheinungen und Gesetze der Stromgeschwindigkeiten des Blutes," 

 Frankfurt, 1858, S. 101. 



3 Arch. f. Physio!., Leipzig, 1886, S. 1. 



4 Skandin. Arch. f. Physiol., Leipzig, 1892-93, Bd. iii. S. 145. 



5 Dodsche med. IVchnwhr., Leipzig, ]S92, S. 109 ; cf. Grehant and Quinquand, Cornet, 

 rend. Hoc. dc hiol., Paris, 1886, p. 159. 



