The Effects of an Acute Reduction in Blood Pressure by Means of Differential Spinal Sympathetic Block on the Cerebral Circulation of Hypertensive Patients 1

Abstract

Recent observations by this group on the cerebral circulation in hypertension (1) have yielded normal values for cerebral blood flow and cerebral oxygen consumption but a marked increase in cerebrovascular resistance. Since the nature of this excessive vascular tone is obscure, it was felt that studies of its behavior during an acute fall in blood pressure might be of interest. Such studies, furthermore, should be pertinent to the rationale of therapy designed to lower the blood pressure in hypertension, since a fall in blood pressure must necessarily be accompanied by a comparable embarrassment of the cerebral circulation except insofar as the high cerebrovascular tone were capable of compensatory relaxation.Differential spinal sympathetic block, achieved by the injection of dilute procaine solution into the lumbar subarachnoid space (2), produces a considerable fall in the blood pressure of many hypertensive patients, presumably by blocking the sympathetic outflow to the abdomen and lower extremities without loss of skeletal muscle tone. This procedure, therefore, offers a means of studying the response of the cerebral circulation to a drop in blood pressure mediated by dilatation in vascular beds remote from the brain. The use of differential spinal block as a possible screening test in selecting patients for surgical sympathectomy provided an opportunity for undertaking these studies on the cerebral circulation. METHODSMeasurements were made in 17 patients with essential hypertension who were being studied on the medical and surgical services as candidates for surgical sympathectomy. Cerebral blood flow (CBF) was determined by means of the nitrous oxide method, and with this value cerebral metabolism in terms of oxygen consumption (CMRo2) and cerebrovascular resistance (CVR) were calculated as previously described (3, 4). Mean arterial blood pressure (MABP) was read from a damped mercury manometer attached to a needle in the femoral artery. Blood gas analyses were made in the Van Slyke-Neill manometric apparatus (5) and pH was measured at 370anaerobically by means of a glass electrode. Values for plasma C02 tension were calculated by means of a nomogram (5).A fine plastic catheter was introduced into the lumbar subarachnoid space. Needles were then placed in the superior bulb of an internal jugular vein and a femoral artery. The patients rested supine for 30 minutes after which control observations were made. Twenty cc. of procaine hydrochloride (0.2% in physiological saline solution) were then introduced intrathecally, usually resulting in diminution of pain sensibility over the lower extremities and well into the intercostal region. This level of anesthesia was kept relatively constant by the instillation of more procaine as needed. The blood pressure usually fell promptly and sometimes markedly, then showed a tendency to remain at a level somewhat above the lowest point reached. When this stabilization had occurred a second determination of cerebral blood flow was made. In some cases the lowest point was...

Cerebral Blood Flow and Cerebral Metabolic Rate of Oxygen Requirements for Cerebral Function and Viability in Humans

“…Two patients with nonfunctional, but viable, brain (group III) also had rCMR02 values> 1.3 mll 100 g-min. This is consistent with studies by Kety et al (1950) and Finnerty et al (1954) demonstrating that reductions in CBF caused neurological symp- toms prior to any change in whole brain oxygen metabolism. Few studies are available concerning the critical value of rCMR02 necessary to maintain cerebral viability in man.…”

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

“…The symptoms experienced by hypertensive patients during tilt were similar to those observed during a sudden fall in arterial pressure from differential spinal sympathetic block (7). These data are further evidence suggesting that such symptoms were the result of cerebral anoxia associated with an inadequate circulation while in this position.…”

The Effects of Carbon Dioxide Inhalation Upon the Cerebral Blood Flow and Cerebral Oxygen Consumption in Vascular Disease 1

“…Various measures which reduce the increased cerebrovascular resistance have been studied. Sympathectomy has been found to result in an 18 per cent decrease (7), high spinal anesthesia, in a 16 per cent decrease (8), and dihydroergocornine, in a 32 per cent decrease (9) in the cerebrovascular resistance in essential hypertension. In the present study, the inhalation of 5 per cent CO2 produced a mean decrease in the cerebrovascular resistance of 35 per cent, revealing CO2 to be as powerful a cerebral vasodilator in essential hypertension as any of the previously studied methods.…”