CHAPTER 31 



The peripheral venous system 



ROBERT S. ALEXANDER 



Department of Physiology, Albany Medical College, 

 Union University, Albany, New York 



CHAPTER CONTENTS 



Anatomical Considerations 



Structure 



Vasa Venarum 



Innervation 



Venous Valves 



Venous Capacity 

 Physiological Characteristics of Veins 



Principles of Venous Hemodynamics 



Venous Distensibility 



Nature of Venous Constriction 

 Assessment of Venomotor Activity 



In Vitro Studies 



Direct Observation 



Inferences from Venous Pressure 



Measurements of Pressure Gradients 



Pressure Measurements in an Occluded Venous Segment 



Pulse Methods 



Venous Distensibility Patterns 



Distensibility by Venous Increment 

 Summary of Venomotor Responses 



insight which anyone may gain into the function of 

 the arterial system by the simple registration of arte- 

 rial blood pressure. As a consequence, very few 

 physiologists or students of physiology have had any 

 personal opportunity to make observations, other 

 than the experiments of Harvey, which could be 

 interpreted with confidence as manifestations of 

 venous function. A major effort of this presentation, 

 therefore, will be to stress the technical problems of 

 obtaining reliable information concerning venous 

 function and to review the degree to which presently- 

 imperfect methods have yielded interpretations that 

 are in substantial agreement. This will lead us to 

 some positive convictions about the functional role 

 of the venous system in spite of many unresolved prob- 

 lems of methodology. 



ANATOMICAL CONSIDERATIONS 



if one were to consult textbooks for information 

 on venous physiology, the impression would be gained 

 that knowledge of this subject has not progressed 

 since the classical observations of William Harvey. 

 The error of this misconception should have been 

 laid to rest by the excellent review of Gollwitzer-Meier 

 (36), in 1932 and the comprehensive monograph of 

 Franklin (32) published in 1937. The bibliography of 

 this monograph, containing well over 1 000 references, 

 is scarcely compatible with the ignorance of the subject 

 which is often reported. It is our impression that a 

 major deterrent to appreciation of our knowledge of 

 venous function stems from a failure to develop valid 

 techniques that can be applied to the venous system 

 with ease and technical accuracy, comparable to the 



Structure 



In general structural pattern, veins are composed of 

 the same elements as are the arteries, but with some 

 important quantitative differences. Surrounding the 

 endothelial lining of the lumen is a network of elastic 

 and collagenous fibers which form a clearly defined 

 intima only in the larger veins; in the smaller veins 

 there is very poor differentiation of the intimal layer. 

 Encircling these intimal fibers is the muscular media, 

 which remains essentially a layer of spirally arranged 

 smooth muscle fibers without any major contribution 

 of elastic fibers. This lack of a heavy elastic investment 

 of the media constitutes the major structural differ- 

 ence between veins and arteries. Externally, the vessel 

 is surrounded bv the meshwork of elastic and col- 



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