The cerebrospinal fluid pressure response to certain acute vascular changes

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.

Caval long‐circuit in the dog

“…Seven experiments were performed by the open-chest technique described by Howarth (1962). Data for three experiments and the mean and range CA VAL LONG-CIRCUIT IN THE DOG for the series are given in Table 1.…”

“…The method of caval long-circuit used successfully for the cat (Grundy & Howarth, 1957;Howarth, 1962) proved unsatisfactory for the dog. The reasons for this are uncertain.…”

“…In the first series of experiments the technique was substantially that described for the cat (Howarth, 1962). After each experiment the apparatus was dismantled and carefully washed, first in detergent (dilute Teepol), then in running water followed by distilled water.…”

“…It should be noted that in the second of these three groups of experiments the azygos vein was intact, while in the other two it was tied. In the cat the superior vena cava carried 25 %, of the combined caval flow excluding azygos flow and 29-30 % when the flow through the azygos vein was included (Grundy & Howarth, 1957;Howarth, 1962).…”

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In order to further studies on the relations between the vascular and cerebrospinal fluid pressures begun in the cat (Grundy & Howarth, 1957;Howarth, 1962), it was found necessary, because of its more suitable intracranial vascular architecture, to perfuse the dog. In addition, it was felt that if a satisfactory preparation of this type could be devised, it would greatly facilitate physiological and pharmacological study of the vascular system of the whole animal, since with but little modification such a preparation would allow simultaneous study of blood flows through selected vascular beds.

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