The Control of the Blood-pressure: (Section of Therapeutics and Pharmacology).

Present conceptions of the control of the general blood-pressure are based on the view that the sympathetic nerves are only constrictor in action and the circulating hormones, adrenaline and vasopressin, only pressor in effect. Surgical treatment of high blood-pressure and allied conditions has been directed accordingly to the removal of portions of the sympathetic system and to the removal of the suprarenal glands or tumours connected with them. Removal of portions of the sympathetic has been successful in relieving attacks of angina pectoris and removal of suprarenal tumours has relieved paroxysmal hypertension. Neither removal of portions of the sympathetic systems nor removal of the suprarenal glands has been successful in reducing continuous hypertension. It is suggested that our conceptions of the control of the blood-pressure need revision.The normal variation in blood-pressure is not sufficiently realized. It may be as low as 85 mm. or as high as 190 mm. About one in every 40 men has a blood-pressure higher than 160 mm. It is suggested that the diagnosis of essential hypertension should never be made unless it is known that the blood-pressure has been rising. A single observation of a high pressure is not enough for the diagnosis.Evidence is described that adrenaline and vasopressin may lower the blood-pressure as well as cause it to rise; similarly there is evidence that the sympathetic nerve supply to the skeletal muscles is dilator rather than constrictor in effect. Hence, all three mechanisms commonly thought of as pressor may also be depressor, and it seems more accurate to think of them as controlling the blood-pressure by raising or lowering it than simply as factors which raise it.