I278 HANDBOOK OF PHYSIOLOGY --" CIRCULATION II 



OUTFLOW MEASUREMENTS 



Venous Outflow Collection 



the simplest and most reliable way to measure mean 

 blood flow of an organ consists in the collection of 

 blood from an opened vein into a graduated cylinder 

 over a measured period of time. Several venous out- 

 flow recorders with intermittent indication of flow 

 rate have been designed (44). In Gaddum's model 

 (34) blood from the opened vein runs into a cylinder, 

 the bottom of which is automatically opened after 

 known periods of time. The collected volume in the 

 cylinder may be recorded making use of Brodie 

 bellows, strain gauges, or other devices for measuring 

 volume or pressure. The Gaddum principle is in fact 

 a continuous recording of graduated cylinder and 

 stop watch readings. The dimensions of the apparatus 

 do not allow measurements lower than 10 ml per 

 min. Readings every 2 sec furnish reliable results. 

 The diameter of the cylinder must be adapted to the 

 amount of blood expected to leave the vein per unit 

 time. The reliability depends mainly on the rapidity 

 of emptying the cylinder between collection periods. 



Drop Recording 



Measurements of flow rates lower than 2 ml per 

 min can be obtained by recording every drop of blood 

 leaving the blood vessel. In most devices the drop 

 closes an electric circuit thereby giving an electro- 

 magnetic signal. Enumeration of drop signals, how- 

 ever, is inaccurate and troublesome. Therefore con- 

 struction of an instrument that records time elapsing 

 between two drops was a great improvement in the 

 method. In 1935 Fleisch (29) described an apparatus 

 in which a motor-driven lever is moved up on a 

 smoked drum until the drop falls. Closure of the 

 electric circuit by the drop initiates the interruption 

 of a coupling link between motor and lever so that the 

 lever returns to its original level. The next period of 

 measurement always begins after 0.12 sec regardless 

 of the height of the lever. It is obvious that such a 

 recorder is more complex than the simple marking 

 apparatus and its construction involves a high degree 

 of precision work. 



With the development of electronics a principle 

 was applied in which the time measurement was 

 performed by measuring the increase of voltage on a 

 condenser during the time between drops. The drop 

 initiates a sudden breakdown of the condenser charge. 



PERSPEX 

 OR POLY- 

 ETHYLENE 



BLOOD 

 SILICONE 



WATER 



fig. i. Schematic drawing of the drop chamber according 

 to Lindgren. A concentric water jacket maintains constant 

 temperature of the blood. [From Lindgren (62).] 



The voltmeter records deflections which are pro- 

 portional to the time between two drops (63a). 



Drop recording has been used mainly to measure 

 venous outflow. The drawback of all outflow measure- 

 ments is loss of blood and the necessity for prompt 

 reinfusion. A definite improvement therefore was the 

 introduction of a drop chamber that can be used in a 

 closed circulatory system (58). The blood from a vein 

 entering the drop chamber falls in drops between 

 electrodes to the bottom and returns to the distal part 

 of the dissected vessel. The air cushion does not seem 

 to introduce any disadvantage in the return of blood 

 to the vein. 



Since electrolysis at the electrode contacts and their 

 coating with coagulated blood often makes readings 

 unreliable, a photoelectric drop recording device has 

 been constructed. A combination of both improve- 

 ments — the enclosed drop chamber and the photo- 

 electric recording of drops — seems to be the best of the 

 fairly simple methods (fig. 1). Lingren"s device (62) 

 uses a drop chamber filled with silicone instead of 

 air, thereby avoiding elastic effects especially impor- 

 tant in arterial blood flow measurements. In recording 

 of pulsatile arterial flow, one should consider also 

 that the device may impair the transmission of pulse 

 waves to the peripheral arterial bed, thereby diminish- 

 ing original mean flow rate. 



