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The observation that a state of elevated blood pressure develops in animals after denervation of the carotid sinus and aortic arch (1) has suggested that certain forms of hypertension in man might similarly be due to a failure of the depres-sor mechanism. Several studies have lent some support to this hypothesis (2, 3, 4). The evidence may be summarized briefly as follows: direct stimulation of the carotid sinus endings in hypertensive patients by digital pressure over the walls of the sinus causes a marked fall in blood pressure; however, alteration of pressure within the carotid sinus by digital compression and release of the common carotid artery below the sinus produces only minimal or negligible changes in blood pressure or heart rate. The conclusion has therefore been drawn that in hypertension there exists a certain degree of insensitiveness of the carotid sinus endings to their physiologic stimulus, namely changes in intravascular pressure within the sinus. The suggestion, furthermore, has been made that in these patients this defect is, in part at least, responsible for the development of the elevation of blood pressure (4, 5). The desirability of reexamining the observations which are the basis of these claims concerning the etiology of hypertension in man is apparent. METHODS AND MATERIAL On a number of patients with elevated blood pressure the carotid sinus test was performed essentially in the manner described by Mandelstamm and Lifschitz (3). The procedures may be briefly described as follows: with the individual prone, the carotid sinus is compressed against the transverse processes of the vertebrae for. a period of 30 to 60 seconds. The common carotid artery is compressed as low in the neck as is possible, attempting to avoid traction on the sinus. The carotid artery was obstructed for periods up to 2 1 Godey and Seegar Fellow in Medicine. minutes. Control observations were made by pressure on an indifferent part of the neck. Simultaneous determinations of blood pressure and pulse rate were made before, during and after such procedures. A sufficient number of observations were made to determine the typical reaction of the individual. Bilateral compression was never employed. Blood pressure was estimated by the auscultatory method; pulse rate, either by counting at the wrist or by plethysmographic recording. Thirty-one patients are included in the present series. Rejections were made of those in whom, for anatomical reasons, it was impossible adequately to compress the sinus or …

THE CAROTID SINUS REFLEX IN PATIENTS WITH HYPERTENSION