CHAPTER 28 



Resistance (conductance) and capacitance 

 phenomena in terminal vascular beds 1 



HAROLD D. GREEN 



CARLOS E. RAPELA 



MARGARET C. CONRAD 2 



Department of Physiology and Pharmacology, Bowman Gray 



School of Medicine, Wake Forest College, Winston-Salem, North Carolina 



CHAPTER CONTENTS 



Resistance Vessels 



Pressure-Flow Relations in Vascular Beds 

 Methods 



Passive curvilinear relationship of pressure-flow plots 

 Mathematical relationships 

 Effects of Viscosity on Pressure-Flow Relationships 

 Effects of Extravascular Pressure on Pressure-Flow Relation- 

 ships 

 Effects of Alterations of Venous Pressure 

 Autoregulatory Control of Resistance Vessels 



Modification of passive pressure-flow relationship by 



autoregulation 

 Artifacts induced in autoregulation studies by pump per- 

 fusion schemas 

 Autoregulation in different vascular beds 

 Reactive hyperemia 



Mechanisms responsible for autoregulation 

 Interpretation of change of vasomotor tone induced by 

 constrictor and dilator agents in vascular beds which 

 demonstrate autoregulation 

 Chemical Effects on Resistance Vessels 

 Extrinsic Control of Resistance Vessels 



Effects of vasomotive agents on total resistance in a 

 vascular bed 

 Segmental Resistances in Vascular Beds 

 Methods 



Effects of Changes of Perfusion Pressure and Venous Pressure 

 on Large Artery and Vein, and Distal Small Vessel 

 Pressures 

 Effects of Extrinsic Agents on Segmental Resistance 



1 Preparation of this chapter and most of the original work 

 reported herein were aided by Grant H-487, National Heart 

 Institute, United States Public Health Service. 



2 Formerly trainee, Cardiovascular Graduate Training 

 Program (HTS-539.2) National Heart Institute, United States 

 Public Health Service; currently Fellow of the American 

 Heart Association. 



Blood Volume in Vascular Beds (Vascular Capacity) 

 Methods 



Effects of Various Factors on Vascular Volume 

 Estimation of Change of Vascular Volume Due to Extrinsic 



Influences 

 Pulsatile Changes in Vascular Volume 



Interpretation of Vascular Behavior from Measurements of 

 Flow, Pressure, and Vascular Volume 



since most vascular beds do not permit direct 

 microscopic study, indirect methods have to be used 

 to evaluate them. In this chapter, the behavior of 

 vascular beds is deduced from recordings of the rate 

 of blood flow, the accompanying small vessel pressures, 

 and the changes in vascular volume that occur as the 

 result of varying the artery to vein pressure difference 

 across the bed and as a result of other intrinsic and 

 extrinsic influences. 



Using the above measurements, the role of the 

 terminal vascular beds is analyzed in terms of the 

 behavior of those segments which determine the 

 resistance to flow through the bed, i.e., the resistance 

 vessels, and those segments which are related to the 

 volume of blood contained in a terminal bed at any 

 moment, i.e., the capacitance vessels. These functions 

 of the terminal vascular beds are shown to be in- 

 fluenced by such physical factors as arterial perfusion 

 pressure, presence of communication with collateral 

 vascular beds, viscosity of the blood, extravascular 

 pressure, venous pressure, by local autoregulation, 

 and by extrinsic factors such as vasoactive agents and 

 the autonomic nerves. 



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