THE MECHANISM OF THE HEART PUMP 



955 



METHODS OF DETERMINING OUTPUT. In a method devised by the author 

 it is possible to determine the output of the left ventricle under all manner of conditions 

 and to vary at will the arterial resistance, the venous pressure, the filling of the heart, 

 or the temperature of the blood supply to -the heart. The arrangement of the apparatus 

 is shown in Fig. 415. Artificial respiration being maintained, the chest is opened under 

 an anaesthetic. The arteries coming from the arch of the aorta in the cat, the innomi- 

 nate and the left subclavian are then ligatured, thus cutting off the whole blood supply 

 to the brain, so that the anaesthetic can be discontinued. Cannulae are placed in the inno- 

 minate artery and the superior vena cava. The cannulae are filled beforehand with a solu- 

 tion of hirudin in normal salt solution so as to prevent clotting of the blood during 

 the experiment. The descending aorta is closed by a ligature. The only path left for 



FIG. 415. Arrangement of apparatus for working on the isolated mammalian 

 heart. ('Heart-lung preparation.') The different parts are not drawn to 

 scale, and the lungs are not shown. (STARLING.) 



the blood is by the ascending aorta and the cannula CA in the innominate artery. 

 The arterial cannula communicates by a T-tube with a mercurial manometer M ' to 

 record the mean arterial pressure, and passes to another T-tube, v, one limb of which 

 projects into a test-tube B. The air in this test-tube will be compressed with a rise 

 of pressure and will serve as a driving force for the blood through the resistance. It 

 thus takes the part of the resilient arterial wall. The other limb of the T-tube passes 

 to the resistance R. This consists of a thin-walled rubber tube (e. g. a rubber finger- 

 stall) which passes through a wide glass tube provided with two lateral tubulures w, w. 

 One of these is connected with a mercurial manometer M 2 and the other with an air 

 reservoir into which air can be pumped. When air is injected into the outer tube, the tube 

 R collapses, and will remain collapsed until the pressure of the blood within it is equal 

 or superior to the pressure in the air surrounding it. It is thus possible to vary at will 

 the resistance to the outflow of the blood from the arterial side. From the peripheral 

 end of R the blood passes at a low pressure through a spiral immersed in warm water 

 into a large glass reservoir. From the reservoir a wide india-rubber tube leads to a 

 cannula, which is placed in the superior vena cavajSTC, all the^ branches of which 



