Servoanalysis of carotid sinus reflex effects on peripheral resistance.

• The baroceptors of the carotid sinus (and arterj') and the aortic arch are the major sense organs which reflexly control the systemic blood pressure. Since the demonstration of the reflex function of these receptors, there has been much work on the responses of the blood pressure, heart, and peripheral vessels to changes in pressure in the carotid arteries and the aorta," on blood flow in particular organs, and on the responses of the sensorj' nerve fibers to alterations of blood pressure. Heymans and Neil have summarized present knowledge of the reflex. In recent years, techniques used to study physical control systems have been applied to the study of biological systems." Two aims of such investigations are to gain insight into the general nature of biological regulation and to see how particular regulations are accomplished. The approach is to state quantitatively the relationship between the stimulus (pressure, temperature, light, etc.) and the response (heart rate, vasomotor activity, pupillary diameter, etc.). A complete description requires analysis of the contributions of each unit: a) the receptor; b) the central nervous system; c) the motor nerves; d) the effector organ. Studies of this kind have been conducted on the pupillary response to light, respiration,' respiratory-circulatory interrelationships, and the stretch reflex, as well as on other systems. The carotid sinus reflex has been studied by techniques involving an electronic analog. In the medullary blood pressure control