The Effects of Twenty Degree Head-Up Tilt Upon the Cerebral Circulation of Patients With Arterial Hypertension Before and After Sympathectomy 1

Abstract

The present study was undertaken in order to measure the effect of a slight elevation of the head and shoulders upon the, cerebral circulation of hypertensive patients following sympathectomy. Twenty degree tilt was chosen because it could be tolerated for 20 minutes, as early as two weeks after the Smithwick sympathectomy.Shenkin and coworkers in 1948 reported that 200 head-up tilt did not alter the cerebral blood flow, cerebral oxygen consumption, and oxygen content of the internal jugular blood in five normal subjects (1). They also reported that, following thoracolumbar sympathectomy, cerebral oxygen uptake and blood flow in hypertensive patients while in the supine position did not differ from the preoperative level (2).We have measured mean arterial pressure, blood flow, and oxygen uptake of the brain, before and after tilt in two groups of patients: (a) 15 patients who had been subjected to bilateral thoracolumbar (D6-L3) sympathectomy, and (b) 18 patients with essential hypertension. METHODSPatients with essential hypertension were selected from the medical and surgical wards of the Hospital of the 1 This study was supported in part by research grants from the National Heart Institute, U. S. grades II to IV (3), fluoroscopic and electrocardiographic evidences of left ventricular hypertrophy, and moderate impairment of renal function as measured by PSP excretion and urea clearance tests. At the time of the tilt study no patient showed either elevation of the blood urea nitrogen above 20 mgm. % or signs of congestive heart failure.The patients studied after sympathectomy were selected at random without regard to the severity of the postoperative postural hypotension. All were ambulatory.Sympathectomies had been completed from two weeks to seven years prior to testing. Ten of the 17 tilts followi'ng sympathectomy were made in the 12 months. immediately after operation, and of these ten, eight were studied within six months after operation.Control measurements of cerebral blood flow, oxygen consumption, and mean femoral arterial pressure (4) were made in the supine position in a room kept as cool as was consistent with the patient's comfort. Accurate control of the environmental temperature was not possible. The patient was then tilted to a 200 head-up position. After three minutes in this position, simultaneously drawn samples of blood from the femoral artery and the internal jugular vein were obtained for analyses of oxygen and carbon dioxide content and blood pH as previously reported (5). When the patient had been in the head-up position for 20 minutes the second cerebral blood flow and oxygen consumption measurement was made. The pressure in the femoral artery during tilt and the vertical distance from the position of the needle to the level of the patients' eyes were recorded. The cerebral arterial pressure was then calculated as reported by Scheinberg and Stead (6). The jugular venous pressure was then subtracted from the calculated cerebral arterial pressure to give "effective" cerebral arterial pres...

Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation

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Cerebral Blood Flow and Oxygen Consumption in Man

“…In moderate hypotension, adequate dilatation of the cerebral vessels occurs, maintaining cerebral blood flow at the normal level (I, 23, 49, 58, 124, 125, 130, I 79, 278 with abnormal values for cerebral perfusion and oxygen uptake (233). Acute hypertensive encephalopathy has already been discussed, and it was mentioned that the cerebral oxygen uptake was reduced in this condition (206,228 lished in numerous studies, demonstrating that this effect is independent of the agent used in producing the hypotension (23,24,29,31,49,54,55,57,80,81,125,128,130,168,179,213,223,224,228,232,332). Thus in hypertensive patients, just as in normotensive subjects, the fall in blood pressure induced by spinal anesthesia (168) was found to cause a similar reduction of cerebrovascular resistance, as, e.g., hexamethonium bromide (55,57,80,213,223,224,332 I 2, 337).…”

The Effects of 1-Hydrazinophthalazine on Cerebral Blood Flow, Vascular Resistance, Oxygen Uptake and Jugular Oxygen Tension in Hypertensive Subjects 1

“…A slight increase in mean oxygen uptake was observed during the head-up tilt. In several of these studies, a reduction in the mean oxygen content of the internal jugular venous blood was observed even though the cerebral oxygen uptake was unchanged (6,7,10).…”

“…For comparison, other patients were given a placebo. The effects of "Apresoline" have been compared with the changes observed after the placebo and during the hypotension induced by differential spinal sympathetic block (6), 20°head-up tilt (7), dihydroergocornine (8), protoveratrine (9), and sympathectomy (10). METHODS 1.…”