PERIPHERAL VENOUS SYSTEM 



1089 



Innervated 

 Serotonin 



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150 t 



• Brachial Artery! 

 o Small Artery 

 x Small Vein |_ 

 Cephalic | 



Denervated 

 Serotonin 



i 



H 



T \ 



A o_o •— - — 



6 100-1 \ /> 



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50 



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25- 



£ 



6 



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• Total 

 "Small Vessels | 



* Arteries #— < 

 Veins /j 



20- 



1.5- 



10- 



0.5 J 



Time in Minutes 



fig. 9. Pressure gradients and resistance changes recorded 

 from the foreleg and paw of a dog that was artificially perfused 

 at a constant rate of flow, demonstrating the application of the 

 Haddy technique (45). 



constriction of the large arteries and veins, and only 

 a minor change in the smaller vessel segment. 



The fact that pressures in minute vessels show con- 

 siderable pulsatile variation (41, 55), presumably 

 associated with a type of venovasomotion (44), renders 

 such measurements of greater qualitative than quan- 

 titative value, since it is difficult to have faith that 

 the discrete vessel from which the peripheral pressure 

 was recorded is accurately representative of the mean 

 pressure in the peripheral venous bed as a whole. 

 This reservation is reinforced by the possibility that 

 the catheter might be wedged so that the recorded 

 pressure represents that of a collateral somewhat 

 remote from the catheter, and also the possibility 

 that the presence of the catheter itself might alter 

 pressure-flow dynamics. Nevertheless, if one keeps 

 these reservations in mind, and takes precautions to 

 be extremely critical of instrumental techniques and 

 record analysis so as to exclude the many possible 

 artifacts which may creep into a method of this type, 

 this appears to be one of the most valuable techniques 

 currently available for studying peripheral venous 



function. It should be appreciated that this method 

 also has the merits of being applicable to human 

 studies (88). 



Pressure Measurements in an 

 Occluded Venous Segment 



Doupe and associates (20) appear to have been 

 the first to have employed the method of isolating a 

 segment of a superficial vein between a pair of com- 

 pressing wedges. If the wedges are placed so that the 

 intervening segment is free of branches, this creates 

 a blind cul-de-sac with an entrapped volume. If a 

 needle is then carefully introduced into this segment, 

 it is possible to record pressures in a system of fixed 

 volume, hence any change in pressure must reflect a 

 change in the muscle tone. In actual practice, it ap- 

 pears to be necessary to distend the vein with a con- 

 siderable volume increment so as to yield basal pres- 

 sures of the order of 40 to 60 cm H 2 in order to 

 achieve significant pressure changes. This also serves 

 the purpose of elevating the recorded pressure out of 

 the range of confusion with extravascular pressure 

 effects. 



A recording from such a preparation is illustrated 

 in figure 10. This illustrates one feature that is con- 

 spicuously demonstrated by this technique: the 

 marked influence of psychic stimulation on venomotor 

 response as the experimental subject witnesses the 

 preparation of some experimental maneuver which 

 he is to undergo. Since responses of the type illu- 

 strated in figure 10 disappear after sympatholytic 

 drugs, there can be little doubt as to their venomotor 

 origin. This technique has been exploited with con- 

 siderable success (14, 68) and is the most direct quali- 

 tative method for studying the venous reactions of 

 the human subject. Because it concerns itself with a 

 unique venous segment, however, it does not appear 

 feasible to standardize the quantitation of pressure 

 responses observed in such studies. 



A variation of this technique is to introduce a small 

 cylindrical balloon into a vein segment and measure 

 pressure changes in this balloon. This obviates the 

 necessity of selecting a segment free of branches, and 

 gives greater confidence that the observations are 

 being obtained from a closed system. As with the 

 method previously described, it also seems essential 

 to distend the balloon to pressure of 30 cm H 2 or 

 higher in order to observe significant changes. Salz- 

 man (81) has successfully applied this technique to 

 the study of the venomotor response to pressoreceptor 

 reflexes. Connolly & Wood (18), on the other hand. 



