MEASUREMENT OF THE CARDIAC OUTPUT 



553 



FIG. I. Chauveau's hemodromo- 

 graph. The arterial stream is 

 directed through the tube, T. 

 The lever, L, senses the force of 

 the stream by means of the vane, 

 r, and transmits the force to the 

 tambour which by air trans- 

 mission to another tambour 

 inscribes the flow (upper record 

 belowj. A simultaneous pressure 

 (lower record) is made by air 

 transmission through the pressure 

 reducer, S. The rubber mem- 

 brane {M) acts to prevent 

 escape of blood from the cannula 

 and as a fulcrum for the lever. 

 [From Luciani (92).] 



quantity the higher it is and the float rides higher as 

 the flow increases. Tlie rotameter gives a linear 

 calibration against flow. Readings may be taken of 

 the height of the float by eye or it may move the core 

 of an inductance transducer to give an electrical 

 signal of the height of the float (21). 



There are three difficulties that the users of rotam- 

 eters are apt to encounter. One is the fact that when 

 a small clot or strand of fibrin lodges on the float there 

 is a sudden and unpredictable change in the cali- 

 bration. This necessitates the use of large amounts of 

 heparin to prevent the formation of fibrin and this, 

 in turn, causes the animal to bleed. Another is the 

 rather high resistance of the instrument, particularly 

 when the flows are rapid. This precludes their 



placement in a vein because of the resulting venous 

 congestion. As a result of the fact that the working 

 pressure in the arteries is so much greater than in the 

 veins, the rotameter may be introduced into arteries. 

 Like the bristle meter described above to measure 

 the cardiac output, the rotameter must be placed in 

 the course of the pulmonary artery and firmly held 

 in a vertical position. Used in this manner it has been 

 shown to give the same values as the Fick (123) and 

 the dye injection methods, and results similar to 

 those with the pulse contour method (91). 



The Potter turbinometer has been used in industry. 

 SarnofT adapted a small model for placing in the 

 aorta (120). It consists of a little turbine which bears 

 a magnet that induces a current in a surrounding 



