CHAPTER 16 



Effects of nerve stimulation and hormones 

 on the heart; the role of the heart in 

 general circulatory regulation 



ROBERT F RUSHMER ! ^^P"''^'"*""' "f Phy^'dogy and Biophysics, University of Washington 



j School of Aledicine, Seattle, Washington 



CHAPTER CONTENTS 



Nature of Increased Contractility 

 Characteristics of Ventricular C'ontractility 



Methods of Analysis 



A Functional Description of "Increased Contractility" 



Contractility, a Generic or a Specific Term 

 The Nature of Spontaneous Cardio\ascular Adjustments 

 Postural Responses 



The Presentricular Sump 

 Relation of Heart Rate to Cardiac Output 

 Cardiovascular Responses to Exertion 



Ventricular Diinensions During Exertion 



Constancy of Stroke Volume During Exercise 

 Neural Mechanisms of Cardiac Control 



Integrated and Local Mechanisms of Cardiovascular Control 

 Summary 



A PRINCIPAL OBJECTIVE of cardios'ascular investigation 

 is tlie understanding of the function and control of 

 the heart in normal people and in patients with 

 various diseases. Analysis of the heart as a pump 

 requires simultaneous measurements of several vari- 

 ables including the effective pressures, the absolute 

 V'olumes of the cardiac chambers, and the velocity 

 and volume flow of blood in and out of the heart. 

 If these factors could be measured accurately, pain- 

 lessly, and safely, normal persons would be the obvious 

 choice for experimental subjects. Unfortunately, of 

 these variables, only pressure can be recorded directly 

 and continuously in human subjects under normal 



conditions. The changing volumes and flow of blood 

 must be estimated from intermittent, indirect deter- 

 minations involving procedures that can alter the 

 measured variables by arousing apprehension or 

 fear. Although volume and flow can be ascertained 

 fairly frequently, the accuracy of many of these 

 measurements depends upon the e.xistence of steady- 

 state conditions, so that the nature of tlie transition 

 from one level of activity to another cannot be readily 

 studied. Without continuous registration of the 

 essential variables, it is often difficult to evaluate the 

 steadiness of the control condition or the sequence of 

 events during the response to an experimental 

 procedure. 



In recent years techniques have been developed 

 for direct and continuous measurement of pressure, 

 dimensions and flow in healthy unanesthetized 

 animals during all manner of spontaneously and 

 experimentally induced cardiovascular reactions. The 

 cardiac responses observed under these conditions 

 have been consistent with available information on 

 cardiac responses in man, but have failed to conform 

 to predictions based on a wealth of experimental 

 data obtained from studies on the exposed heart of the 

 anesthetized dog. 



The nature of the cardiac adaptations observed in 

 heart-lung preparations or in exposed hearts has had 

 a dominant influence on the concepts of cardiac 

 control for a great many years. As early as 1884 

 Howell & Donaldson (ig) presented evidence that 



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