Reflexogenic Areas of the Cardiovascular System

REFLEXOGENIC AREAS OF THE CARDIOVASCULAR SYSTEM C. HEYMANS* After the discovery ofthe pulmonary circulation by Ibn-an-Nafis in the thirteenth century and by Servetus in the sixteenth century and the discovery ofthe systemic circulation ofthe blood by Harvey in 1628, arterial pressure was first measured by Stephen Hales in 1733 and then by Poiseuille in 1828 and Ludwig in 1847, wno recorded arterial blood pressure by means ofa glass tube or a mercury manometer connected with an artery. As a result ofnumerous observations, the physiologists concluded that the arterial pressure was subject to regulation and tried to clarify the mechanisms. In 1836 Astley Cooper observed that compression of both common carotid arteries, which induced a fall ofarterial pressure in the head and brain, provoked acceleration ofthe heart rate and a rise in the systemic arterial pressure (1). This observation was confirmed by Magendie in 1838 (2). Experiments done between 1877 and 1926 by several workers (3-10) showed that a rise ofblood pressure in the carotid-cephalic circulation induces bradycardia and a fall ofthe systemic arterial pressure, while a drop in the carotid-cephalic pressure provokes acceleration ofthe heart rate and a rise ofsystemic arterialpressure. Allthese experimentalobservationswere considered to be a demonstration ofa direct sensitivity ofthe cardiovascular centers to blood pressure variations. The direct central regulation and homeostasis ofarterial pressure by means ofthe action ofblood pressure variations on the cardiovascular centers was thus generally accepted. But as early as 1900 Pagano (11) and Siciliano (12), ofthe laboratory of Spallitta in Palermo, published an interesting series of experiments. Siciliano showed that while clamping of both common carotid arteries induced tachycardia and a rise in the systemic arterial pressure, clamping of * Professor, Department ofPharmacology, University ofGhent, Belgium. 409 the branches ofthe common carotids, the external and internal carotid, and the occipital arteries did not provoke the same responses. Siciliano also pointed out that while clamping ofthe common carotid arteries induced tachycardia and a rise in the systemic arterial pressure, clamping of the internal carotid artery had the opposite effects. Pagano stated that increase ofpressure in the common carotid artery circulation induces cardiac slowing and a fall in the systemic arterial pressure by means ofa common carotid reflex mechanism and not by a directaction ofpressure on the cardio-vascular centers. Siciliano and Pagano concluded that these reflex actions on the cardiovascular centers occur by means ofthe influence ofblood pressure variations on receptors located in the common carotid artery. Pagano also stated that the most sensitive reflexogenic area ofthe common carotidarterytopressurevariations was located close to the common carotid bifurcation. These interesting observations and conclusions were, however, not considered by the physiologists and were contradicted by Kaufmann in 1912 (13), who ligated a common carotid artery in situ under its bifurcation and inserted a cannula in the lower end ofthis carotid artery. Kaufmann observed that rise or fall ofpressure did not affect the systemic arterial pressure reflexly, and thus he rejected the statements ofSiciliano and Pagano. In 1923 Kisch and Sakai, working in the laboratory ofH. E. Hering, reconsidered the experiments of Siciliano and Pagano and also contradicted their observations and conclusions (14). In 1866 Czermak had observed that mechanical stimulation of an area in the neck ofhuman beings induces a fall ofheart rate and blood pressure and concluded that this was due to compression ofthe vagus nerve (15). His now well-known Vagusdruckversuch was thus introduced as a clinical test. But in 1870 Concato stated that it isnot stimulation ofthe vagus nerve in the neck, but mechanical compression ofthe carotid artery, which provokes this effect (16). This statement was supported in 1900 by Pagano and by Winterberg (11, 17). In 1912 Sollmann and Brown observed that traction on the cephalic end of the common carotid artery provokes a reflex bradycardia and fall of systemic arterial pressure (18). These investigators tried without success to locate the origin and pathways ofthese reflex mechanisms. Experiments performed in different laboratories between 1924 and 1955 have shown that the blood pressure is regulated by the reflex action ofthe 410 C. Heymans · Cardiovascular Reflexes Perspectives in Biology and Medicine · Spring i960 arterial pressure itselfon pressure-sensitive receptors located in the vascular walls ofthe aortic arch and carotid sinus areas...