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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



RISE IN PRESSURE 

 ^-^ mm Hg 



/ 



TIME IN MINUTES 



PNEUMOGRAM 



^.x*s/Wv/Wv-s->M^ •*?} 



fig. io. Pressure changes recorded from a segment of a superficial vein of the forearm that had 

 been isolated between wedges and kept at constant volume. [From Duggan et al. (21).] 



were unable to record temperature reactions in 

 superficial veins in man by this technique, even 

 though veins adjacent to that containing the balloon 

 exhibited obvious caliber changes. The author has 

 similarly been unsuccessful in attempting to get suffi- 

 cient response for accurate analysis in a variety of 

 applications of this technique to various dog prepa- 

 rations. Further studies are in order to determine the 

 full potentialities and limitations of this method. 



Another type of method which is based on the 

 same principle was introduced by Hooker (54) and 

 has been adapted to human studies by Wallace (87, 

 88). By use of a pressure cuff on the arm, pressure 

 is first developed to occlude venous drainage and 

 produce venous congestion, and then further elevated 

 to stop all blood flow to the arm. Venous pressures 

 measured between 2 and 8 min after obstruction to 

 blood flow show a slow decline, presumably due to 

 capillary transudation. Yenomotor stimulation pro- 

 duces pressure changes superimposed on this slow 

 decline. Although this method has yielded clear quali- 

 tative evidence of venomotor reactions (64), and 

 possibly has some merits of simplicity, it introduces 

 a number of complicating features, such as prolonged 

 ischemia, which would vitiate precise quantitation 

 and therefore place it in an unfavorable position as 

 compared with other methods that are available. 



Pulse Methods 



Pulsatile changes in the volume contained within 

 a vascular segment will produce pulsatile pressure 

 changes, the magnitude and rate of transmission of 



which are determined by the elastic properties of the 

 vessel wall. Since muscle tone is one of the factors 

 influencing elasticity of the venous wall, this suggests 

 another possible approach to an assessment of ven- 

 omotor tone. Unfortunately, the pulsations which 

 occur normally in the venous system are too small 

 in magnitude and too complex in etiology to be sus- 

 ceptible to this type of analysis. 



Peterson (72, 73) has overcome this limitation by 

 generating pulses artificially with a high speed in- 

 jection system. There results a momentary peak of 

 pressure which increases in magnitude as venous tone 

 increases. As yet, limited applications of this type of 

 method have been reported. The author has had 

 extensive experience with a related phenomenon that 

 he has referred to as the ""acceleration transient" 

 which appears at the moment of initiating a constant 

 speed injection into a vein. It is clear that many de- 

 tails at the tip of the injection cannula can influence 

 the pressure peak produced. The exact dimensions 

 and orientation of the injection orifice in relation to 

 the vessel lumen are of critical importance in deter- 

 mining the exact pattern of pressure development, 

 and this problem can be gravely augmented by the 

 tendency for some veins to develop a segment of local 

 constriction in the area of cannulation. Extending 

 the orifice to a site somewhat remote from the point 

 of cannulation introduces problems of proper orien- 

 tation of the injection tip, and also requires pressure 

 recording through a separate channel in order to 

 prevent the flow resistance of an elongated injection 

 cannula from dominating the pressure recording. 

 Although the potentialities of such a pulse method 



