1282 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



TO FLOAT RECORDER 



THERMOMETER 



COLLECTING 

 CUFF 



HIGGINSON S SYRINGE 



fig. 5. Plethysmograph for the hand according to H. 

 Barcroft. The hand is enclosed in a loose-fitting surgical rubber 

 glove. [From Barcroft & Swan (10).] 



during this time the volume of the hand increases 

 uniformly, indicating that the venous reservoir is not 

 filled to an extent which would impair capillary flow. 



The recording system used in Barcroft's experiments 

 consists of a small spirometer writing on a smoked 

 drum. The rubber tubing connection between the 

 plethvsmograph and spirometer is filled with air. The 

 use of a spirometer makes it necessary to have air in 

 the rubber tubing connections between spirometer 

 and plethysmograph. A small cylinder on top of the 

 plethysmograph allows control of the water level of 

 the apparatus. An electrically recorded tracing of 

 spirometer movements is used in our laboratory mak- 

 ing use of the electromagnetic principles applied in 

 the rotameter recording technique (see below). 



The use of small rubber cuffs as plethysmography 

 lias been recommended recently by Dohm. Models 

 suitable for measurements on forearm and calf, with 

 which it is possible to secure good venous-occlusion 

 records and to measure blood flow during muscular 

 exercise, are especially useful on moving subjects (41). 

 The plethysmographic cuffs are made of thin-walled 

 rubber 5 cm wide. The filling pressure can best be 

 about +40 mm H.,0 and increase with 1 per cent 

 volume changes of the extremity segment up to about 

 50 mm H a O. The pressure was measured by a con- 

 denser manometer. 



Avoiding any plethysmographic devices, Whitney 

 (86) proposes the use of a strain gauge mounted di- 

 rectly on the limb. It records the changes of tension 



due to changes in blood volume. This occlusion tech- 

 nique furnishes results not remarkably different from 

 those obtained by using water or air plethysmography. 

 Assuming that the limb is distended only in the dia- 

 metrical direction, changes of circumference can be 

 converted directly into volume changes. However, 

 corrections for compression of the limb by increases 

 in blood volume are deemed to be necessary. 



A serious objection to the venous-occlusion method 

 is discussed by Gaskell & Burton (35), who observed 

 a decrease of blood flow in the dependent leg. These 

 authors believe in a venovasomotor reflex elicited 

 by distension of veins. Since the venous-occlusion 

 method relies on the fact that blood entering the 

 region of measurement is collected in the veins, 

 thereby distending them, it is important to the valid- 

 ity of the method to study the influence of venous 

 distension upon vascular reflexes. 



Greenfield & Patterson (45) showed in experiments 

 on the forearm at different states of venous distention 

 that the blood flow, as measured with their venous- 



Phase 1 



Phase 2 



Phase 3 



fig. 6. Events during venous occlusion plethysmography. 

 Actual inflow = actual outflow + apparent inflow. Each divi- 

 sion on vertical scale for inflow and outflow represents 1 ml/ 100 

 ml of forearm per min. Total duration of collection: 130 sec. 

 [From Greenfield & Patterson (45).] 



