METHODS OF MEASURING BLOOD FLOW 



'3°9 



FLOW 



Y-< 



w < 



fig. 21. Diagram of the standard transducer-tube bristle 

 flowmeter of Brecher. a: Flowmeter cannula similar to that of 

 Brecher & Praglin (12), with improved socket, b: The same 

 model with "zeroing" cylinder. Total length, 50 mm. For 

 further description see text. [From Brecher (9, 10).] 



equation 10 is preponderant. The streamlined ob- 

 stacle, however, offers much lower resistance to the 

 flow; its sensitivity is therefore smaller, and its calibra- 

 tion curve approaches linearity in that the deflection 

 is proportional to v l -\ thus indicating that it is chiefly 

 due to viscous drag. It may be noteworthy that the 

 authors found the output voltage of the transducer 

 tube to respond to cooling by the streaming blood so 

 that the base line of the records was not sufficiently 

 stable. 



The most extended use of the 5734 tube-bristle 

 flowmeter in arteries and veins was made by Brecher 

 et al. Their "standard model" was published by 

 Brecher & Praglin (12) and is shown in figure 21 with 

 two additional improvements described by Brecher 

 (10). The system consists of four parts A', Y, W, '/., 

 which are screwed together. The transducer tube is 

 held by the parts X and W which form a metal screw 

 socket pressing the two lead washers R\ and R< 

 against the lower rim and shoulder of the tube's 

 metal shell. In this way, the tube is fixed, and perm- 

 anent electrical contact is established between tube 

 plate and grounded cannula. Also seepage of fluid 

 from part Z to the lead wires M is prevented. Part 

 Z, as "head" of the assembly, is ligated into the blood 

 vessel and connected with A' by part Y. Heads of 

 various dimensions are available for use in blood 

 vessels of different diameters. The small bristle B is 



20 to 35 mm long; it can be made of glass, nylon, or 

 metal. The natural frequency of the transducer 

 system with the bristle amounts to about 200 cps. 

 The side tube A' is used for the removal of air bubbles 

 and for attaching a manometer for pressure record- 

 ing. Temperature changes of the transducer tube 

 caused by the streaming blood are prevented by the 

 long stationary fluid column in the parts Y and Z. 

 When the meter is inserted into the blood vessel, zero 

 flow can be determined at any time by means of the 

 "zeroing" cylinder G (fig. 216) without stopping the 

 blood flow. The cylinder position is controlled by the 

 handle (?; it can be moved forward beyond the 

 bristle tip in order to protect the bristle from de- 

 flection by the flow. 



For blood-flow recordings in large arteries, 

 especially in the trunk of the pulmonary artery, 

 Brecher & Hubay (11) developed a modification 

 of the standard bristle flowmeter which can be in- 

 serted without clamping the vessel (fig. 22). The 

 device consists of three main parts A, B, C. The 

 transducer tube is fixed in C by cement. The most 

 characteristic part of the device is the lip D which is 

 introduced into the vessel through a "buttonhole" 

 opening with little loss of blood. The vessel wall is 

 then firmly held between D and plate E, the latter 

 being pressed by screw nut F. In order to protect 

 the bristle against damage during the insertion of lip 

 D into the vessel, the tip of the bristle U is withdrawn 

 behind lip D by screwing part C backward. The 



fig. 22. Brecher's bristle flowmeter modified by Brecher & 

 Hubay (11) for use in large arteries, especially in pulmonary 

 artery trunk. Total length, 75 mm. a: Diagram of longitudinal 

 section, b: Application to pulmonary artery. For description 

 see text. [From Brecher (10).] 



