[Pressure in the jugular vein and right atrium and the cerebral hemodynamics of the healthy human being exposed to postural effects].

Ten test subjects were catheterized and exposed to head-up and head-down tilts at 10, 30 and 75% for 5 min each to measure blood pressure in the upper bulb of the internal jugular vein and right atrium. Blood acid-base equilibrium, hemoglobin content and oxygen saturation were also determined. In the head-up position at 75 degrees the jugular pressure decreased, remaining positive (2.8 mm Hg) in most cases, whereas the atrial pressure fell down to reach the subatmospheric level. In the hea-down position the jugular pressure increased in proportion to the tilt angle, amounting to 32,2 mm Hg at 75 degrees; the atrial pressure changed in a different fashion: in 7 cases it increased and in 3 cases decreased. Throughout the test the oxygen arteriovenous difference in the brain and the acid-base equilibrium in the outflowing blood remained essentially unchanged. This reflects autoregulation of the cerebral blood flow and its adequacy to metabolic requirements.