The intracranial volume-pressure response was measured in 61 patients undergoing continous monitoring of intraventicular pressure. This test, which determlnes the increase in intracranial pressure induced by an addition of 1 ml in ventricular CSF volume in 1 sencond, yields information concerning spatial compensation in patients with intracranial space-occupying processes. On the basis of variability tests, a change in volume-pressure response of 2 mm Hg/ml was accepted as significant. Pronounced enlargement of the ventricles interferes with the test. In patients with intracranial hypertension, intravenous mannitol (0.5gm/kg) and intramuscular betamethasone (26 mg) both reduce the volume-pressure response significantly more than they reduce intracranial pressure. This suggests that these agents favorably alter the configuration of the volume-pressure curve.

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SYNOPSIS Twenty patients with aneurysms of the internal carotid artery underwent temporary clamping, in turn, of the internal and then the common carotid artery. Cerebral blood flow, internal carotid artery pressure, and the EEG were recorded to assess the probability of cerebral ischaemia after permanent ligation. With this method of monitoring the cerebral circulation, 17 of the 20 patients had a permanent carotid ligation without neurological deficit; in the other three ligation was contraindicated. Although a correlation was observed between the reduction of cerebral blood flow and the fall in internal carotid artery pressure caused by temporary clamping (P < 0 01), the scatter of data was too wide to predict cerebral blood flow from the change in carotid artery pressure. Similarly, EEG slowing was usually associated with low cerebral blood flow but exceptions occurred. Ligation was safe when, during temporary clamping, cerebral blood flow exceeded 40 ml/100 g/min, but was deemed unsafe when flow was less than 20 ml/100 g/min. In the range 20-40 ml/100 g/min, consideration of the internal carotid artery pressure permitted more patients to be safely ligated than if the decision had rested on changes in cerebral blood flow alone.Permanent ligation of a carotid vessel in the neck is a widely used method of treating certain intracranial aneurysms and recent studies have confirmed its efficacy in providing lasting protection from recurrent subarachnoid haemorrhage (German and Black, 1965;Sahs et al., 1973). Although a more simple operation than intracranial clipping of an aneurysm, it carries the risk of producing ischaemia of the ipsilateral cerebral hemisphere, reported to occur in 3000 of the aggregate series of 785 carotid ligation operations in the Co-operative Aneurysm Study (Nishioka, 1966). In 21% of these cases the signs ofischaemia were delayed for more than 48 hours after ligation, and recent evidence suggests that deficits of delayed onset are more likely to be permanent than are ischaemic complications occurring in the first few hours after ligation (Landolt and Millikan, 1970 . Although such patients are spared the risk of hemiplegia, their original condition remains untreated, and they face the hazard of this and of an alternative

SYNOPSIS Intermittent additions of 0 05 ml saline were made into the lateral ventricle of anaesthetized, ventilated baboons at regular intervals during continuous inflation of a supratentorial extradural balloon. Close correlation was observed both between the increase in ventricular fluid pressure (VFP) immediately after the injection and the volume in the balloon (P < 0001); and between the increase in ventricular pressure and the pressure immediately before the injection (P < 0001). This change in ventricular fluid pressure, which is termed the volume-pressure response (VPR), helps to delineate the stage reached on the intracranial volume-pressure curve, and is therefore a measure of the capacity of the intracranial contents to compensate for the volume changes produced by an expanding intracranial lesion. The VPR is currently being used in patients and the clinical implications of confirming its validity experimentally are therefore discussed.