Effect of intracranial hypotension on cerebral blood flow

Cerebral Blood Flow in Low Intracranial Pressure Headaches-What is Known?

Headaches attributed to low cerebrospinal fluid (CSF) pressure are described as orthostatic headaches caused by spontaneous or secondary low CSF pressure or CSF leakages. Regardless of the cause, CFS leaks may lead to intracranial hypotension (IH) and influence cerebral blood flow (CBF). When CSF volume decreases, a compensative increase in intracranial blood volume and cerebral vasodilatation occurs. Sinking of the brain and traction on pain-sensitive structures are thought to be the causes of orthostatic headaches. Although there are many studies concerning CBF during intracranial hypertension, little is known about CBF characteristics during low intracranial pressure. The aim of this review is to examine the relationship between CBF, CSF, and intracranial pressure in headaches assigned to low CSF pressure.

Two-photon fluorescence microscopy of cerebral hemodynamics

Under physiological conditions, neuronal activity is tightly coupled to hemodynamics of the surrounding microvessels. Conversely, most brain diseases are associated with a disturbance in neurovascular coupling. Measuring the hemodynamic response of the microvascular network to neuronal stimulation in vivo involves two major challenges: maintaining a stable systemic physiological state in the animal and imaging with sufficient temporal and spatial resolution to capture the hemodynamic changes across the three-dimensional cortical microvascular network. Two-photon fluorescence microscopy allows imaging of intact cortex in situ at micrometer spatial and microsecond temporal resolution. However, this modality necessitates focal opening of the skull because of its high scattering of light waves. This protocol describes in detail the requisite surgical preparation and physiological maintenance of an adolescent rat with a closed cranial window. Two-photon fluorescence laser scanning microscopy is then used to image the hemodynamic response of the microvasculature of the primary somatosensory cortex to electrical stimulation of the forepaw, with the end goal of quantitative analysis of brain hemodynamics.

Normal pressure hydrocephalus and cerebral blood flow: a review

Normal pressure hydrocephalus is a neurological disease which poses both diagnostic and therapeutic problems for the clinician. The measurement and characterisation of cerebral blood flow has been proposed as a tool for resolving such problems as well as elucidating its pathophysiology. We review the results of studies in which this tool has been applied to normal pressure hydrocephalus patients and consider the merits of the techniques that have been utilised. Finally, consideration is given to feasible future studies and the methods that could be employed in the study of cerebral blood flow and metabolism in patients with normal pressure hydrocephalus.

Cerebral hemodynamics in patients with normal pressure hydrocephalus: correlation between cerebral circulation time and dementia

Regional cerebral blood flow and regional cerebral circulation time were measured in 13 demented patients with chronic hydrocephalus, mostly normal pressure hydrocephalus. The average hemispheric, frontal, and temporal cerebral blood flows were significantly reduced. The average regional cerebral circulation time values were significantly prolonged in the frontal, temporal, and thalamic regions, most markedly in the frontal white matter, where periventricular lucency was observed on computed tomography. Clinical improvement was obtained in all patients after operation. While postoperative regional cerebral blood flow values did not change compared with preoperative ones, postoperative regional cerebral circulation time values were significantly reduced in all the regions measured, and most markedly in the frontal white matter. The present results suggest that microcirculation in the frontal lobe is closely correlated with dementia in association with pressure exerted on the nerve fibers in the frontal white matter in patients with normal pressure hydrocephalus.

Cerebral blood flow in normal pressure hydrocephalus

A xenon-133 method was used to measure cerebral blood flow (CBF) before and after cerebrospinal fluid (CSF) removal in patients with normal pressure hydrocephalus (NPH). Preliminary results suggested that shunting should be performed on patients whose CBF increased after CSF removal. There was a significant increase in CBF in patients with NPH, which was confirmed by the favorable outcome of 88% of patients shunted. The majority of patients with senile and presenile dementia showed a decrease or no change in CBF after CSF removal. It is suggested that although changes in CBF and clinical symptoms of NPH may have the same cause, i.e., changes in the cerebral intraparenchymal pressure, there is no simple direct relation between these two events. The mechanism underlying the loss of autoregulation observed in NPH is also discussed.

Cerebral blood flow in patients with normal-pressure hydrocephalus before and after shunting

Cerebral blood flow (CBF) was measured by xenon-133 inhalation and single photon emission tomography in 17 demented patients with normal-pressure hydrocephalus before and after shunt treatment. All patients had a decreased conductance to outflow (C out) of cerebrospinal fluid as measured by lumboventricular perfusion (C out less than 0.12 ml X mm Hg-1 X min-1). Computerized tomography (CT) scanning, clinical assessment, and neuropsychological grading were performed pre- and postoperatively. The preoperative CBF studies revealed abnormal flow patterns in all patients. Fourteen patients showed moderate-sized, large, or very large central low-flow areas, and four patients had reduced flow bilaterally in the occipital and contiguous temporoparietal regions. After shunting, six patients had a significant reduction in the size of the central low-flow area on the CBF map, agreeing well with the changes of ventricular size on the CT scan. All six patients showed an improvement in either clinical or neuropsychological grading. In 10 of the remaining 11 patients flow patterns were essentially unchanged; one patient deteriorated further. Four of these 11 patients improved on postoperative clinical or neuropsychological testing. Thus, a positive correlation was found between the changes in CBF and the reduction of the ventricular size on the CT scan, but changes in CBF as measured by the present technique did not accompany improvement in the functional state in all patients.

Evaluation of treatment of normal-pressure hydrocephalus

Ten patients with dementia due to normal-pressure hydrocephalus were evaluated prospectively according to a planned, longitudinal protocol for 4 to 12 months. Information recorded at each visit included clinical history, medical and neurological examination, psychometric scoring by Mini-Mental Status Questionnaire, measurement of ventricular size and local cerebral blood flow, and partition coefficients (local lambda changes) (1 lambda) by xenon contrast computerized tomography scanning. Cerebrospinal fluid shunting was carried out in eight cases. Serial evaluations were repeated at intervals up to 8 months after shunting, and demonstrated that the ventricles decreased in size and periventricular hypodensities decreased. White matter 1 lambda values and blood flows and cortical gray matter flows progressively increased for 3 months after shunting, and remained increased except for one case complicated by chronic alcoholism. Clinical recovery correlated with improved cerebral perfusion. There were returns of urinary continence and improvements in gait and usually in activities of daily living. Mentation was the last factor to improve. Factors negatively influencing cerebral perfusion and clinical recovery were shunt failures and various contributing causes of dementia.

Pathogenesis of normal-pressure hydrocephalus--preliminary observations

Eight cases with well-documented normal-pressure hydrocephalus were studied prospectively for 6 months by history, neurological examinations, Mini-Mental Status tests, xenon-contrast computed tomography measurements of local cerebral blood flow, and cerebral xenon solubility expressed as partition coefficients. Local cerebral blood flow and local partition coefficients were reduced throughout frontal and temporal lobes, basal ganglia, and thalamus. Cerebrospinal fluid shunting procedures were carried out in seven cases. As a result, local cerebral blood flow and local partition coefficients increased toward normal, particularly in frontal white matter, frontotemporal cortex, and basal ganglia. Ventricular size became reduced and mental status improved. Local partition coefficient values were reduced by increased tissue water because low values confirmed cerebrospinal fluid diffusion into white matter, which resolved after shunting. Patients likely to benefit from shunting, including shunt failures requiring revision, were detected.

The clinical effect of lumbar puncture in normal pressure hydrocephalus

Owing to all the difficulties involved in selecting patients with normal pressure hydrocephalus for shunt-operation, a cerebrospinal fluid-tap-test (CSF-TT) is introduced. Psychometric and motor capacities of the patients are measured before and after lumbar puncture and removal of 40-50 ml CSF. Patients fulfilling criteria for normal pressure hydrocephalus were compared to patients with dementia and atrophy shown by computed tomography. Normal pressure hydrocephalus patients showed temporary improvement after lumbar puncture. The extent of the temporary improvement appeared to be well correlated with the improvement after shunt operation. Accordingly, the CSF-TT seems to be of value when selecting those patients who will probably benefit from a shunt operation.

Noninvasive measurement of cerebral vasopasm in patients with subarachnoid hemorrhage

Regional cerebral blood flow (rCBF) was measured as fast flow clearance (F1) and the initial slope index (ISI2) after inhalation of 133Xe in 30 patients with subarachnoid hemorrhage (SAH). Vasomotor responsiveness to reduction in end-tibal PECO2 was examined in those patients who could carry out this procedure satisfactorily as a test for the presence or absence of vasospasm. F1 and ISI2 were significantly reduced in patients with recent SAH compared to 35 age-matched normal volunteers. The degree of reduction of F1 and ISI2 correlated directly with severity of the neurological deficit graded according to the Hunt and Hess rating scale. Topographic reductions of rCBF correlated with angiographically demonstrated vasospasm or intracerebral hematoma. The degree of impairment of cerebral vasomotor responsiveness to reduction of PECO2 by hyperventilation also correlated with the severity of vasospasm demonstrated angiographically in 16 patients. The reductions of rCBF values were maximal during the first week after SAH but returned gradually toward normal by the 5th week. Individual patients with SAH whose lowest F1 values were above 50 ml/100 g brain/min tolerated surgical intervention best. Non-invasive measurements of rCBF after SAH appear to be helpful in estimating the presence and time course of vasospasm, in recognizing the development of normal pressure hydrocephalus, and in planning medical and surgical management.

Amnestic-confabulatory syndrome in hydrocephalic dementia and Korsakoff's psychosis in alcoholism

The clinical course of six alcoholics with Korsakoff's psyter shunt operation. The initial clinical state as well as the symptom improvement showed important similarities between the Korsakoff group and the hydrocephalic dementia group, who improved after shunt operation. Fantastic confabulation and appraxia were only observed in the hydrocephalic dementia group. Psychometrically, both groups showed a similar degree of improvement of the initially impaired verbal memory while only the hydrocephalic dementia group showed impairment of spatial abilities indicating a constructional apraxia. It is suggested that the similarities of the two conditions are related to dysfunction of diencephalic and temporal-limbic structures. The constructional and general apraxia as well as the fantastic confabulation in hydrocephalic dementia indicate a cortical, especially frontal cortical, dysfunction in this disorder.

Syndrome of normal pressure hydrocephalus: possible relation to hypertensive and arteriosclerotic vasculopathy

A patient with clinical features of idiopathic normal pressure hydrocephalus, who responded dramatically to shunting, was found a necropsy to have a severe hypertensive and arteriosclerotic vasculopathy with multiple lacunar infarcts. There was no pathological evidence of thickened leptomeninges, fibrosis of the arachnoid villi, or Alzheimer's disease. An abnormal absorption mechanism was demonstrated with cisternography and by an increase in the concentration of homovanillic acid in the cerebrospinal fluid. It is suggested that vascular changes may play an important role in the pathophysiology in some cases of normal pressure hydrocephalus.

The effects of increased intracranial pressure on flow through major cerebral arteries in vitro

The effect of transmural pressure (TMP) (intraluminal minus extraluminal pressure) on flow was measured for 26 isolated major cerebral arteries from human autopsies. The maximum flow rate through an artery was determined by the perfusion pressure (PP), the maximum vessel caliber, and the presence and magnitude of external resistances. Assuming a diastolic PP of 85 mm Hg, intracranial pressure increases above 33±2 SEM mm Hg (45±3 cm H 2 O) resulted in a reduction of flow through these arteries. For atherosclerotic arteries, flow was reduced by 50% at a TMP of 12±1 mm Hg; for nonatherosclerotic arteries, the critical TMP for 50% flow reduction was 20±1 mm Hg. Flow ceased at a TMP of +3 mm Hg for small (cerebellar) arteries to -7 mm Hg for large (posterior cerebral) arteries. For grossly atherosclerotic arteries, this closing pressure was as low as -15 mm Hg. When two arteries were cannulated and perfused in parallel, preferential flow reductions of up to 50% were noted in one of the arteries with no flow change in the other at the same TMP. This preferential narrowing depended on the relative sizes and degree of atherosclerosis of the two arteries.

Wall thickness to lumen diameter ratios were obtained for all arteries and their relevance to the possibility of active closure was discussed.

Effect of cerebrospinal fluid shunts on intracranial pressure and on cerebrospinal fluid dynamics. 2. A new technique of pressure measurements: results and concepts. 3. A concept of hydrocephalus

Part 2 describes measurements of intracranial cerebrospinal fluid (CSF) pressure in 18 adult patients with CSF shunts, all pressure measurements being referred to a horizontal plane close to the foramina of Monro. All 18 patients had normal CSF pressure by lumbar puncture; however, in one patient an intracranial pressure of +280 mm was subsequently measured after pneumoencephalography. Twelve patients had pre-shunt CSF pressures measured intracranially: 11 ranged from +20 to +180 mm H(2)O and one was +280 mm H(2)O in the supine position. In the upright posture nine patients had values of -10 to -140 mm H(2)O, while three others were +60, +70, and +280 mm H(2)O. After CSF shunting in these 18 patients the pressures were -30 to +30 mm H(2)O in the supine position and -210 to -370 mm in the upright position. The effect of posture on the siphoning action of these longer shunts in the erect, adult patient is a major uncontrollable variable in maintenance of intracranial pressure after shunting. Other significant variables are reviewed. In Part 3 a concept of the hydrocephalus phenomenon is described. Emphasis is placed on the pressure differential (P(d)) and force differential (F(d)) causing pre-shunt ventricular enlargement and post-shunt ventricular size reduction. The site of P(d), which must be very small and not to be confused with measured ventricular pressure, P, must be at the ventricular wall.

Adult hydrocephalus. Evaluation of shunt therapy in 80 patients

✓ Eighty adults with hydrocephalus were treated with a shunt operation. Twenty-four had nonabsorptive hydrocephalus with obstruction at the level of the basal cisterns and 56 had hydrocephalus plus cerebral atrophy without apparent obstruction to the flow of cerebrospinal fluid. Thirty-four patients improved but in only 16 (20%) was the improvement dramatic. The material was analyzed to identify criteria for future case selection. History, evidence of tissue damage, and thickness of cerebral mantle were considered important. Antibiotics reduced infection rate from 19% to 3%.