HANDBOOK OF PHYSIOLOGY '^ CIRCULATION 



its quantitation. He measured blood pressure for the 

 first time and showed its variation with heart beat 

 and respiration in the arteries, and its relatively low 

 level in veins. He estimated the rate of circulation, 

 and the slow velocity of venous blood. Further, by 

 using wax injections, he estimated the volume of 

 cardiac chambers and of the aorta. By his direct 

 method of measurement, he estimated systolic blood 

 pressure in humans to be around 7} 2 f^ct of blood, 

 which is a reasonable approximation as balanced 

 against atmospheric pressure only. Practical applica- 

 tion of these observations had to wait a century until 

 Scipione Riva-Rocci (1863-1937) developed the 

 mercury sphygmomanometer (1896) which is the 

 principle for our current clinical instruments. It is 

 interesting that Hales's "haemastaticks" probably 

 developed from his earlier studies on "vegetable 

 staticks" in which he ingeniously measured sap pres- 

 sure in plants. To minds that are intelligent and 

 imaginatively curious, all living things can be found 

 to yield associative concepts. 



Steadily accelerating progress now came in our 

 knowledge of the functional activity of the cardio- 

 vascular system. Much was sparked by the realization 

 of the work of Antoine Lavoisier (i 743-1 794) who 

 before his death as a martyr of the French Revolu- 

 tion had founded modern chemistry by his quantita- 

 tive studies on the significance of oxygen, and who 

 showed the real relation between respiration, the 

 oxygen transport of the blood, and bodily heat forma- 

 tion. This came more than a century after Robert 

 Boyle (162 7- 1691) studied the function of air in 

 respiration and combustion, and after Lower and 

 Mayow showed that the change from venous to 

 arterial blood in the lung is due to something ab- 

 sorbed from air. 



The great and handsome teacher Franjois 

 Magendie (i 783-1 855) showed the importance of the 

 blood in transport of nutriments, and his pupil James 

 Blake (1815-1893), the brilliant Englishman who 

 migrated in the gold rush to California, measured 

 circulation time. Magendie's greatest pupil was 

 Claude Bernard (18 13-1878) who discovered vascular 

 nerves and the functions of vasoconstriction and 

 vasodilation in regulating blood supply to the various 

 parts of the body. 



German precision studies on the cardiovascular 

 system began with Ernst Weber (i 795-1878) and 

 his brother Eduard (i 806-1 871) who measured the 

 pulse wave in 1825. Carl Ludwig (i 816- 1895), the 

 superb .self-effacing teacher, promoted rapid progress 

 i)y his invention of the kymograph for recording 



blood pressure changes under varying conditions. 

 Karl Vierordt (1818-1884) introduced sphygmo- 

 graphic methods for indirectly measuring blood 

 pressure, thus laying the basis for practical clinical 

 applications. He showed the influence of blood vol- 

 ume, pulse rate, and respiration on the rate of blood 

 flow, while Ludwig followed up an observation of 

 Harvey's in devising methods for perfusing organs, 

 including the heart. 



The practical applications of Harvey's work to 

 medicine began with the recognition of pathological 

 details involving the cardiovascular system. Giovanni 

 Lancisi (1654-1720) laid the basis for cardiac pathol- 

 ogy with his observation of valvular lesions and of 

 cardiac dilatation in correlation with symptoms of 

 disease. This was extended by Giovanni Morgagni 

 ( 1682-177 1 ) in describing mitral stenosis and heart 

 block. In France, Raymond Vieussens (1641-1715) 

 had already noted the circulatory effects of aneurisms 

 and the symptoms of aortic regurgitation. 



When William Withering (i 741-1799) introduced 

 digitalis for cardiac dropsy in 1785, he greatly ad- 

 vanced the practical applications of Harvey's work 

 on the heart and circulation by showing that some- 

 thing could be done when the cardiovascular system 

 is not functioning properly. But he did not differen- 

 tiate between cardiac and renal dropsy. This was done 

 by Richard Bright (i 789-1858) in 1827, and further 

 ramifications of the applications of Harsey's work 

 began. These led to the realization of the effects of 

 "hardening of the arteries," and later to various 

 aspects of hypertension which we are still vigorously 

 exploring. 



The clinical significance of blood pressure, as a 

 ready guide to diagnosing disturbances of the cardio- 

 vascular system, led to systematic efforts to analyze 

 the factors involved. This was best done by J. R. 

 McLeod (1876-1935) in the first edition of his famed 

 text on physiology, which appeared in 1920. Here he 

 well surveyed the five factors which control blood 

 pressure: /) the pumping action of the heart, as de- 

 pendent on its rate and output per beat; 2) the pe- 

 ripheral resistance offered to blood by the various 

 parts of the circulation, with its balanced nervous 

 and chemical control; j) blood volume, and its varia- 

 tions under varying conditions; 4) blood viscosity 

 and its variations, and 5) the elasticity of blood vessel 

 walls, with their variations especially with age. Harvey 

 had vaguely anticipated many of these factors, and 

 it is remarkable how slowly they were studied in rela- 

 tion to the practical significance they have in clinical 



