No abstract

No abstract

No abstract

A perfused cat preparation is described which permits controlled and independent alterations of certain major vascular variables. The effects of such alterations upon the cerebrospinal fluid pressure are examined. The information obtained together with that derived from experiments on non-perfused animals is used to explain the cerebrospinal fluid pressure response to temporary obstruction of a vena cava. An increase in a caval pressure produces a sustained rise of cerebrospinal fluid pressure which resists lowering, and the rise of the latter pressure accompanying an increase in cardiac input is due mainly to the increase of central venous pressures. A decrease of cardiac input produces first a fall followed by a rise of cerebrospinal fluid pressure. When the input is restored the pressure rises steeply, ex­ceeding the resting level. None of these effects is due to changes in central venous pressures. In the non-perfused animal a caval obstruction produces a rise of distal caval pressure and a fall of cardiac input and the result of these two opposing influences is usually an increase of cerebrospinal fluid pressure. The rise of caval pressure raises the cerebrospinal fluid pressure by increasing the regional intracraniovertebral venous sinus pressure. On releasing an obstructed inferior vena cava a supernormal rise of cerebrospinal fluid pressure is observed, as after restoration of a reduced cardiac input. This response is dependent upon a mechanism restricted to the cranial end of the neuraxis and appears to be caused by a brief increase of cerebral blood flow. On releasing an obstructed superior vena cava a supernormal rise of cerebrospinal fluid pressure is not seen.

No abstract