頭蓋内圧亢進時の脳灌流圧と脳循環障害 : 特にテント上・下加圧による差異について

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Disturbance of cerebral circulation during intracranial hypertension is not only caused by vasoparalytic effect of the cerbral vessel, but also caused by alteration of the perfusion pressure. The perfusion pressure, which is the difference between mean arterial pressure and cerebrospinal fluid pressure (Miller), does not always indicate real perfusion pressure during intracranial hypertension. Appearance of intercompartment pressure gradient during intracranial hypertension might be important to control perfusion pressure as reported by Symon et al. In the mechanism of alteration of cerebral circulation during intracranial hypertension, the change of the real perfusion perssure, vasopressor response and vasoparalysis have to be observed. In 40 mongrel dogs under pentobarbital anesthesia with artificial respiration (PaCO_2 35-38 mmHg), pressures at the epidural space, the cisterna magna, the sagittal sinus, the femoral artery, the cerebral pial artery, the vein and cerebral tissue fluid were continuously recorded during intracranial hypertension induced by incremental inflation of the extradural balloon placed at the right frontal region or at the posterior fossa. The perfusion pressure was analysed by means of two factors: One is upstream perfusion pressure (mean arterial pressure - pial arterial pressure) and the other is downstream perfusion pressure (pial arterial pressure - pial venous pressure). Each perfusion pressure was divided by mean arterial pressure as indicated by the formula in Fig. 2. In several dogs, cerebral circulation was studied by the method of single dye passage reported by Brock. Main results of the experiment are as follows: (1) The intracranial pressure is not markedly changed by the inflation of the balloon until the tissue fluid pressure reaches to 40-50 mmHg. It is due to a buffering effect of the cerebrospinal cavity. At this stage, the epidural pressure is about 50-70 mmHg and the perfusion pressure is kept at 40 mmHg. When tissue fluid pressure rises over 50 mmHg, even small amount inflation of the balloon produces marked elevation of intracranial pressure and decrease of the perfusion pressure. At this pressure point, inter-compartmental pressure difference is observed; the pressure difference between supratentorial and infratentorial cavities appears and then the right-left hemispheric intercompartment pressure difference is observed. When the tissue fluid pressure is over 70 mmHg which is higher than pial venous pressure, the perfusion pressure is decreased, the upstream perfusion index is 46 and the downstream perfusion index becomes 10. The difference between the upstream perfusion index and the downstream perfusion index indicates blood stasis in cerebral circulation. Following these phenomena, marked change of cerebrovascular tone into vasoparalytic state is observed. (2) By the inflation of infratentorial balloon, the buffering effect of the cerebrospinal cavity disappears at a lower tissue fluid pressure level (less than 40 mmHg) and vasopressor response appears at an early stage in order to keep the upstream perfusion pressure. Acute vasoparalysis occurrs at 60 mmHg of the tissue fluid pressure. According to these results, it might be concluded that (1) disturbance of the cerebral circulation during intracranial hypertension is not only induced by total intracranial pressure, but also by intercompartment pressure gradient and the balance between upstream and downstream perfusion pressures, (2) under the intracranial hypertension induced by infratentorial balloon inflation, buffering effect of the cerebrospinal cavity is smaller, intercompartment pressure gradient is larger, vasopressor response appears in earlier stage and vasoparalytic state is observed at lower point of tissue fluid pressure compared with the results of the supratentorial balloon inflation group. (3) the alteration of cerebral blood flow during intracranial hypertension is induced by unbalance between upstream and dow
日本脳神経外科学会の論文

頭蓋内圧亢進時の脳灌流圧と脳循環障害 : 特にテント上・下加圧による差異について

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