Supratentorial pressures. Part I: Differential intracranial pressures

Dynamic supratentorial pressure changes may differentially alter tissue pressure and intraventricular fluid pressure. To evaluate these pressures, we used a floppy cuff intracerebral catheter and an intraventricular catheter in the cat and rhesus monkey. Baseline intraventricular pressures exceeded intracerebral pressure in both species. Intraventricular pressure was 3-4 mmHg in cats and 6-14 mmHg in monkeys, while the intracerebral pressure was in the range 0-4 mmHg in both. Saline injection into the spinal or cranial subarachnoid space resulted in a greater increase in ventricular fluid pressure, and the time for return to baseline was one and a half times longer in the intraventricular compartment. Jugular venous and abdominal compression resulted in a greater rise in the ventricular pressure than intracerebral pressure. Inflation of subdural balloons and intracerebral injection of silicone caused a differential pressure across the brain with the pressure being greatest in the ipsilateral hemisphere and lowest in the contralateral hemisphere. Rapidly evolving epidural masses produced varied results. We did not evaluate compensatory pressure changes in these animals. Those pressures that involve cerebrospinal fluid (CSF) dynamics alter intraventricular pressure more than tissue pressure. Alternatively, rapidly forming masses tend to increase tissue pressure near the mass more than intraventricular pressure.