[Regulation of cerebral circulation in an upright posture of the human trunk]

The functional mechanisms responsible for orthostatic tolerance of cerebral circulation in the normal man and in ambulatory and bedridden neurosurgical patients were investigated, using the following methods: cerebral blood flow by means of xenon-133 clearance, measurement of brain perfusion pressure, ventricular pressure, acid-base equilibrium in the blood flowing in and out of the brain, determination of cardiac output and stroke volume, electroencephalography, and rheography of cerebral and peripheral vessels. In the normal men and patients with compensated neurosurgical pathologies, the transfer into the head-up position induced small changes in the systemic and cerebral regional circulation. This was associated with complex reactions of the vascular system triggered by the receptors of the sinocarotid area. The normal response of the vascular system to the orthostatic load involved dilatation of cerebral and constriction of peripheral arteries, tachycardia, increased central venous pressure, moderate decrease of brain perfusion pressure and intraventricular pressure. In vascular pathological reactions constriction of peripheral arteries and veins was disturbed; cardiac output and stroke volume, cerebral blood flow velocity, central venous and intraventricular pressures were decreased.