Intracranial pressure: cerebrospinal fluid dynamics and pressure-volume relations.

Continuous measurement of the intracranial pressure (ICP) is routine in todays evaluation of various intracranial diseases and increased ICP is a common therapeutical problem in neurosurgical patients. Still, very little is known about the patho-physiological and biomechanic events that lead to increased ICP. ICP is governed by 1) the resistance to absorption of cerebrospinal fluid (Rout), 2) the production rate of CSF (If) (taken together Rout and If are referred to as the "CSF dynamics"), and 3) the pressure in the Sagittal Sinus (Pss) in accordance with the equation: ICP = If X Rout + Pss. When an intracranial mass grows the cranio-spinal volume buffering capacity is exhausted and the ICP subsequently rises. This event has been imitated in experiments and is described by the classical exponential pressure-volume curve. In a semilogarithmic coordinate system the curve will be linear and if one exchanges the abscissa and ordinate (x = log ICP, y = volume) the slope is the pressure-volume index (PVI). In normal adults PVI = 25 ml and defines the volume that theoretically will increase the ICP tenfold when injected into the CSF space. The main goal of the present study was to analyse the ICP in accordance with the above mentioned principles by measurements of Rout and the PVI. Furthermore, to evaluate the PVI method (synonymous with the "bolus injection" method) described by Marmarou and coworkers. By this method a bolus of a few milliliters of fluid is injected into the ventricles via an intraventricular cannula. PVI is computed based on the immidate ICP rise. The following slowlier ICP decrement defines the Rout. Another goal was to analyse whether measurements of the ICP pulse amplitude, which cancels the need of manipulations of the CSF space, could replace PVI measurements. Finally, to evaluate whether or not CT of the brain depicts pressure-volume relations and Rout in adult patients with hydrocephalus. The study comprised 63 patients with subarachnoid haemorrhage, cranio-cerebral injury or so-called normal-pressure hydrocephalus. The following variables were measured: 1) ICP, 2) pulseamplitude, 3) PVI and 4) Rout. The latter was measured by means of the PVI method and in some instances for reasons of comparison with the constant rate infusion technique and "controlled withdrawal". The main conclusions of the studies were: 1) For estimates of PVI the bolus injection technique was applicable. For Rout measurements the method was only safe at relatively low ICP levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Surgery of arachnoid pouches.

An anecdotal presentation of some features of subarachnoid pouches stresses the variable clinical and morphological features. Hydrocephalus is commonly associated but is not always a cause nor a result of the pouches. The nature of the valvular action is unclear but most probably usually takes the form of plugs of nervous tissue, compression of perivascular spaces in the depths of sulci or else meningeal flaps forming slits in the CSF pathways. The nature of the filling force is almost certainly pulsatile and dependent upon venous impulses generated within the thoraco-abdominal cavities. Treatment may need to be directed against the pouch, or the hydrocephalus. Treatment of the valvular mechanism alone by dissection is frequently sufficient. Opening the pouch widely to the ventricular system may also be of value. Post-operative surveillance is necessary.

Pressure-volume conditions in patients with subarachnoid and/or intraventricular hemorrhage.

Pressure-volume conditions were studied in 17 patients with subarachnoid and/or intraventricular hemorrhage, who underwent continuous intracranial pressure (ICP) monitoring. The pressure-volume index (PVI) technique was used. The interrelationship between the ICP pulse amplitude and compliance was also examined. All patients were admitted in Hunt and Hess Grades II to V, and 11 had a proven aneurysm. The ICP was above 15 mm Hg in all patients during some part of the monitoring period. The pressure-volume conditions were abnormal in all patients. Median PVI was 12.7 ml (5.8 to 40.0 ml). The PVI did not correlate with ICP: the PVI based on bolus injection was significantly greater than PVI based on fluid withdrawal. The ICP pulse amplitude varied from 1.5 to 15 mm Hg and rose concomitantly with increasing ICP. Considering the pulsatile shift in intracranial blood volume as an endogenous bolus that increases ICP from the diastolic (Pdiast) to the systolic (Psyst) level, an equation was derived from the PVI model that describes the relationship between the Psyst:Pdiast ratio and the PVI.

Tracer study on a paracellular route in experimental hydrocephalus.

Considering the possibility of a paracellular pathway for edema resolution, we studied the intracerebral movement of proteins and ionic lanthanum in rats with experimental hydrocephalus. Hydrocephalus was induced by injection of kaolin suspension into the cisterna magna. After induction of hydrocephalus, horseradish peroxidase (HRP), microperoxidase (MP), or lanthanum chloride (LaCl3) were perfused into the ventricle system. HRP and MP were localized mainly in the intercellular spaces between ependymal cells, glial cells, and in perivascular spaces and were restricted by endothelial tight junctions. Ionic lanthanum (La3+), however, penetrated these tight junctions and moved between the blood and CSF cavities by paracellular pathways. These findings indicate that in obstructive hydrocephalus, the tight junctions may constitute part of a paracellular pathway for the transendothelial movement of small solutes, although they prevent the movement of larger molecules.

[Intracranial pressure recording. Principles, technics, results and possibilities]. / Die Registrierung des intrakraniellen Druckes. Grundlagen, Techniken, Ergebnisse und Möglichkeiten.

Methods for continuous ICP recording were further developed. Intraventricular pressure measurement requires puncture of the brain, and is susceptible to infection. For routine applications, therefore, preferential use is made of miniaturized pressure transducers which, without the need to open the dura, are simply implanted epidurally. In the absence of disorders of blood clotting, no complications, in particular no infections, were observed in more than 900 measurements. In the case of rapidly growing intracranial space-consuming processes, considerable intracranial pressure differences giving rise to intracranial mass shifts and even incarceration occur. These pressure gradients can also be measured and treated clinically. The pathological intracranial pressure curve shows typical wave dynamics with A, B, C and D waves, and pulsation changes. In intensive care, measurement permits rapid detection of complications, selective treatment and prognostic information, including the temporal definition of brain death. In neurological and neuropediatric diagnosis, ICP measurement differentiates between active hydrocephalus and cerebral atrophy/dystrophy, and here, as also in cystic cerebral changes, subdural effusions, etc., helps clarify the indication for surgery. In the case of "pseudo tumour cerebri", too, ICP measurement permits objectivation. In addition, it is also possible to determine directly the intracranial reserve space and the CSF dynamics (bolus/infusion test, pulse wave analysis).

Cerebrospinal fluid flow abnormalities in patients with neoplastic meningitis. An evaluation using 111indium-DTPA ventriculography.

Cerebrospinal fluid flow dynamics were evaluated by 111Indium-diethylenetriamine pentaacetic acid (111In-DTPA) ventriculography in 27 patients with neoplastic meningitis. Nineteen patients (70 percent) had evidence of cerebrospinal fluid flow disturbances. These occurred as ventricular outlet obstructions, abnormalities of flow in the spinal canal, or flow distrubances over the cortical convexities. Tumor histology, physical examination, cerebrospinal fluid analysis, myelograms, and computerized axial tomographic scans were not sufficient to predict cerebrospinal fluid flow patterns. These data indicate that cerebrospinal fluid flow abnormalities are common in patients with neoplastic meningitis and that 111In-DTPA cerebrospinal fluid flow imaging is useful in characterizing these abnormalities. This technique provides insight into the distribution of intraventricularly administered chemotherapy and may provide explanations for treatment failure and drug-induced neurotoxicity in patients with neoplastic meningitis.

Evidence of active regulation of cerebrospinal fluid acid-base balance.

To test the passive transport hypothesis of cerebrospinal fluid (CSF) [H+] regulation, we altered the relationship between plasma [H+] and the electrical potential difference between CSF and blood (PD) by elevating plasma [K+] during 6-h systemic acid-base disturbances. In five groups of pentobarbital-anesthetized dogs, we increased plasma [K+] from 3.5 to an average of 7.8 meq/l. Hyperkalemia produced an increase in the PD of 6.3 mV by 6 h with normal plasma acid-base status (pHa 7.4), of 8.3 mV with isocapnic metabolic acidosis (pHa 7.2), of 5.3 mV with isocapnic metabolic alkalosis (pHa 7.6), of 9.2 mV with isobicarbonate respiratory acidosis (PaCO2 61 Torr) and of 5.7 mV with isobicarbonate respiratory alkalosis (PaCO2 25 Torr). The change in CSF [H+] at 6 h in each group was the same as that observed in normokalemic animals (Am. J. Physiol. 228: 1134-1154, 1975). This result is not consistent with the passive transport hypothesis. The CSF-blood PD is therefore not an important determinant of CSF [H+] CSF [H+] homeostasis must result from some form of active transport control.

Simultaneous cerebral and spinal fluid pressure recordings. 2. Cerebrospinal dissociation with lesions at the foramen magnum.

Simultaneous intraventricular and intraspinal pressure recordings in erect patients with obstructive lesions of th CSF pathways reveal differences in pressure which are frequently transitory and produced by pulsation. In non-acute cases without papilloedema but with suspected hindbrain hernia delay in equalization after pressure pulses may be demonstrated, and after Valsalva's manoeuvre differences between the head and the spine may be generated transiently and be responsible for clinical symptomatology. The particular clinical features related to hindbrain hernia are syringomyelia, cough headache, cough syncope, and lower cranial nerve signs with oscillopsia and cerebellar ataxia. Correction of the pressure dissociation is often associated with marked clinical improvement. It is suggested that this form of testing may be of relevance as an indication for operation and also for monitoring the progress of post-operative patients.

Computed tomography and pneumoencephalography compared to conductance to outflow of CSF in normal pressure hydrocephalus.

The conductance to outflow of CSF (Cout) was measured in 66 patients with normal pressure hydrocephalus (NPH). All patients were investigated with computed tomography (CT); 34 of the patients also had pneumoencephalography (PEG). Periventricular hypodensity on CT indicates a low Cout. Cortical sulci smaller than 1.9 mm on CT indicate a low Cout, while wide cortical sulci do not exclude a low Cout. There was a good correlation between ventricular size on CT and PEG, but the ventricular size is unrelated to Cout. No findings on PEG indicate a low Cout.

New aspects of cerebrospinal fluid dynamics in humans investigated by sequential gamma camera cisternography, with data evaluation by the digital multichannel analyzer. 2nd part: pathology of cerebrospinal fluid flow in the subarachnoid space of the brain convexity.

The use of the sequential gamma camera technique with evaluation of the stored information in the digital analyzing system to investigate CSF dynamics quantitatively has given interesting new information about the circulation in the epicortical SA space. The streaming of I131HSA-labelled CSF in a protracted bolus or bulk was submitted to quantitative and temporal analysis by defining the activity maxima and their amounts as well as their times of appearance. Different modalities of activity evolution in various regions make it possible to define three main types of circulatory disturbance, which are: 1. Global epicortical inhibition, 2. circumscribed epicortical inhibition by a) restriction of the SA space, b) dilatation of the SA space, and 3. gamma cisternographic asymmetry, apparently due to restriction, with a fully functioning but dilated SA space and no real inhibition. The pathological conditions in the SA space leading to these different flow disturbance modalities are presented, and the necessity to perform quantitative and temporal analysis for definition of the functional flow conditions is emphasized.

Effect of chronic hypovitaminosis A on water metabolism in the weanling rat.

To study water imbalance reported to occur in vitamin A deficiency, chronic hypovitaminosis A was produced in 7-week old rats by feeding deficient or adequate vitamin A (12 or 256 mug/kg body weight/day, respectively) for a comparison period of 6 weeks. In the case of the deficient rats, these were partially depleted of their vitamin A stores prior to feeding the 12 mug intake. At the termination of the comparison period, the deficient rats exhibited elevated cerebrospinal fluid pressure and lower plasma and liver vitamin A concentrations. Based upon kinetics of a single intrajugular injection of 3H2O and 14C-inulin, total body water, extracellular water and renal clearances were lower in vitamin A deficient rats. However, when these criteria were expressed on a body weight basis, there were no significant differences. The turnover of total body water was reduced in the hypovitaminotic A rats. The results are discussed in terms of an inhibitory effect of vitamin A deficiency on growth.