Changes in epidural pulse pressure in brain oedema following experimental focal ischaemia

This study was carried out to clarify the changes of pulse pressure of the intracranial pressure pulse wave in ischaemic brain oedema. Intracranial pressure and PP were measured in two groups of anaesthetized dogs; 1) increased volume of cerebrospinal fluid by cisternal saline injection (control group), 2) brain oedema caused by focal ischaemia (oedema group). Ischaemia was induced by 2 hours of occlusion of the anterior, middle cerebral and internal carotid arteries. The canine focal ischaemic model showed consistent ischaemic damage in the caudate nucleus and produced brain oedema successfully. PP increased linearly with rising ICP to 35 mm Hg, and PP in the oedema group was significantly smaller than that in the control group at the same ICP value. The slopes of the regression equation of ICP and PP were significantly different between the oedema and control group (oedema: 0.057 +/- 0.029, control: 0.106 +/- 0.009), mean +/- SD, P less than 0.005). These results suggest that PP is easily affected by ischaemic brain oedema, which indicates increase of the brain tissue in the cranium. We conclude that PP is affected even at the same ICP value when intracranial components have altered.