SUMMARY This paper details the results of experimental studies, on 16 dogs with artificiallyinduced intracranial space-occupying lesions, of the systemic vascular responses and the intracranial pressure changes (both in the supratentorial and infratentorial compartments) induced by increasing intracranial pressure. The changes produced were divided into two phases such that phase 1 detailed the alterations observed from the start of the balloon inflation up to the initiation of the systemic pressor response. Phase 2 recorded those alterations which occurred durig, and immediately after, the period of systemic hypertension (see Fitch et al., 1977). The changes observed during phase 1, and presented in this communication, were those of increasing intracranial pressures and decreasing mean arterial pressure and heart rate. These alterations were associated with decreases in supratentorial perfusion pressure and increases in transtentorial pressure gradient and arrhythmia index.In the classical experiments in which systemic hypertension and bradycardia were related to increased intracranial pressure, the increase in intracranial pressure was produced by the infusion of fluid into the subarachnoid space (Naunyn and Schreiber, 1881;Cushing, 1901;Kocher, 1901). Under such conditions, the increase in intracranial pressure is uniformly distributed throughout the intracranial space. For example, when this method of increasing intracranial pressure is used, the pressure in the subarachnoid space overlying the anterolateral surface of one hemisphere has been found to be equal to the pressure in the cisterna magna over the range 0-100 mmHg (Coroneos et al., 1971). In clinical practice, however, this is a rare form of increased intracranial pressure, although conditions pertaining during pneumoencephalography may approximate closely to it. Much more commonly, the clinician is concerned with alterations in intracranial pressure produced by space-occupying pathology such as tumour or haematoma. Thus, the question of the greatest interest to the clinician is that regarding the re-1 Address for correspondence and reprint requests: Dr William Fitch, University Department of Anaesthesia, Glasgow Royal Infirmary, Castle Street, Glasgow,G4 OSF, Scotland. Accepted 29 March 1977 lationship between the systemic circulatory changes and intracranial pressure when the latter is abnormal due to the effects of intracranial space-occupying pathology with concomitant distortion of intracranial structures.The following experiments were performed in order to obtain further information on the relationships existing between the systemic vascular changes noted with increasing intracranial pressure and the intracranial pressure changes found in different intracranial compartments in the presence of an intracranial mass lesion.
MethodsTwo groups of investigations were carried out on anaesthetised dogs. In each animal an artificial space-occupying lesion was created by the placement of a small balloon in the extradural space. Volume changes of this...
