PROGRESSIVE BRAIN COMPRESSION - CHANGES IN VITAL PHYSIOLOGICAL VARIABLES, CORRELATED WITH BRAIN-TISSUE WATER-CONTENT AND BRAIN-TISSUE DISPLACEMENT - EXPERIMENTAL MR-IMAGING IN DOGS

Continuous recording of vital physiological variables and sequential M R imaging were performed simultaneously during continuous expansion of an epidural rubber balloon over the left hemisphere in anaesthetised dogs. Balloon expansion led to a progressive and slightly nonlinear ri se in intracranial CSF pressures and a fall in local perfusion pressur es. Changes in systemic arterial pressure, pulse rate, and respiration rate usually appeared at a balloon volume of 4% to 5% of the intracra nial volume (reaction volume), together with a marked transtentorial p ressure gradient and MR imaging changes consistent with tentorial hern iation. Respiratory arrest occurred at a balloon volume of approximate ly 10% of the intracranial volume (apnoea volume), which was associate d with occlusion of the cisterna magna, consistent with some degree of foramen magnum herniation. Increase in tissue water was observed begi nning at approximately the reaction volume, presumably due to ischaemi c oedema, due to the fall in perfusion pressures.