HISTORICAL DEVELOPMENT OF CARDIOVASCULAR PHYSIOLOGY 



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conditions. We still have great difficulty estimating 

 the volume output of the heart. 



Toward the middle of the nineteenth century the 

 acceleration of scientific knowledge about the heart 

 and circulation increased markedly. The Webers 

 discovered the cardio-inhibitory function of the vagus, 

 and Etienne Marey (1830- 1904) showed a relationship 

 between blood pressure and cardiac action. Albert 

 Bezold (1836-1868) discovered the accelerator nerves 

 to the heart, and Johann Czermak (1828-1873) 

 slowed the heart by pressure near the carotid sinus. 

 Here then was the background for much recent and 

 current study on the balanced functions of the 

 autonomic nervous system and of the significance of 

 the carotid sinus in regulating the circulation. Chemi- 

 cal factors involved were not appreciated until the 

 twentieth century studies of Walter Cannon (1871- 

 1945) which opened the way for the concept of ad- 

 renergic factors, and of Otto Loewi (b. 1873) which 

 prepared the way for the idea of cholinergic influences. 



When the neck of a mammal is compressed around 

 the carotid arteries, the animal becomes drowsy. This 

 was known to the ancients. Indeed this procedure was 

 sometimes used in antiquity to produce a kind of 

 anesthesia, and the carotid arteries were known as the 

 "arteries of sleep" (the word '"carotid" is derived 

 from a Greek word ineaning "deep sleep"). It is 

 amazing that this important phenomenon was not 

 systematically studied until recently. Rufus of 

 Ephesus, a Greek physician at the beginning of our 

 era, believed the phenomenon was due to pressure on 

 nerves near the carotid arteries. No one commented 

 further until Heinrich Irenaeus Quincke (1842-1922) 

 showed that pressure on the carotids produces slowing 

 of the heart. He thought this was caused by stimula- 

 tion of the vagi. The baro-receptor reflex function of 

 the carotid sinus was described by H. E. Hering in 

 1924. Then the phenomenon was vigorously studied 

 by the great Nobel laureate Belgian physiologist, 

 Corncille Hevmans, and his pupils. They described 

 full details of chemo- and baro-receptor reflexes of the 

 cardiovascular system, and have beautifully sum- 

 marized their investigations.^ Many of these were 

 based on skillful cross-circulation experiments which 

 had been devised by Professor Heymans' father, 

 Jean-Frangois Heymans, who founded the renowned 

 pharmacological institute in Ghent, and the Archives 

 Inter nationales de PharmacoJynamie et de Therapie. 



* C. Heymans & E. Neil, Rejie xogenic Areas of the Cardio- 

 vascular System. London: Churchill, 1958, 279 pp. 



Meanwhile Adolph Fick (1829-1 901) had de- 

 scribed the basic principle for estimating cardiac out- 

 put, and John Scott Burdon-Sanderson had observed 

 electrical action currents in heart contractions and 

 had recorded them. This was developed by Augustus 

 Waller (1856-1922) and brought to the high pitch of 

 current electrocardiography by the string galva- 

 nometer of Willem Einthoven (1860-1927). The 

 clinical applications of these great advances were 

 promptly made by James Mackenzie (1853-1925) 

 and Thomas Lewis (1881-1945). The functional im- 

 portance of the capillaries was explored by August 

 Krogh (1874- 1 949) with prompt clinical application 

 again by Thomas Lewis. 



While quantitative analysis of blood gases had been 

 made in 1837 fc'V Heinrich Magnus (1802- 1870), it 

 was Eduard Pfliiger (1829-1910) who showed the 

 respiratory changes which occur between blood and 

 tissues as the blood circulates. The respiratory func- 

 tion of the blood in circulation was fully explored by 

 Joseph Barcroft (1872- 1947), with momentous con- 

 sequences for current studies on aviation and space 

 physiology. This field had been opened by the pioneer- 

 ing work of Paul Bert (1833-1886), although it took 

 a couple of generations to catch up with the 

 importance of what he showed. 



Both as a skilled comparative physiologist and as a 

 pioneering embryologist, Harvey had been fascinated 

 by the problem of the origin and conduction of the 

 heart beat. He had observed the beginning of the 

 beat in the embryonic chick, and he had carefully 

 analyzed, as well as he could with his naked eyes, the 

 spread of the contraction over the adult heart. It was 

 not until two centuries had passed, however, that 

 Hermann Stannius (1808- 1883) analyzed by means 

 of his famed ligatures the automaticity and rhyth- 

 inicity of the various parts of the heart, with the beat 

 apparently originating at the sinus node. Walter 

 Gaskell (1847-19 1 4) investigated the nerve supply to 

 the heart, while Wilhelm His, Jr. (i 863-1 934) and 

 Albert Kent (1863-1945) showed the function of the 

 auriculo-ventricular bundle in bridging contractions 

 from the auricle to the ventricle. The problem of the 

 origin and conduction of the heart beat was analyzed 

 in a classic paper in the first issue of Physiological 

 Reviews (1921), by my revered teachers, Walter J. 

 Meek and J. A. E. Eyster of Wisconsin. Certain as- 

 pects of this matter led to a realization of the im- 

 portance of venous pressvu'e in regard to filling the 

 heart. Harvey had indicated the existence of venous 

 pressure factors in cardiac filling. 



