Cerebrospinal fluid pulse pressure method: a possible substitute for the examination of B waves

OBJECT: The appearance of numerous B waves during intracranial pressure (ICP) registration in patients with idiopathic adult hydrocephalus syndrome (IAHS) is considered to predict good outcome after shunt surgery. The aim of this study was to describe which physical parameters of the cerebrospinal fluid (CSF) system B-waves reflect and to find a method that could replace long-term B-wave analysis. METHODS: Ten patients with IAHS were subjected to long-term registration of ICP and a lumbar constant-pressure infusion test. The B-wave presence, CSF outflow resistance (R(out)), and relative pulse pressure coefficient (RPPC) were assessed using computerized analysis. The RPPC was introduced as a parameter reflecting the joint effect of elastance and pulsatory volume changes on ICP and was determined by relating ICP pulse amplitudes to mean ICP. CONCLUSIONS: The B-wave presence on ICP registration correlates strongly with RPPC (r = 0.91, p < 0.001, 10 patients) but not with CSF R(out). This correlation indicates that B waves-like RPPC-primarily reflect the ability of the CSF system to reallocate and store liquid rather than absorb it. The RPPC-assessing lumbar short-term CSF pulse pressure method could replace the intracranial long-term B-wave analysis.     

Preoperative spinal hydrodynamics versus clinical change 1 year after shunt treatment in idiopathic normal pressure hydrocephalus patients

Nineteen consecutive cases treated for idiopathic normal pressure hydrocephalus (iNPH) with ventriculo-peritoneal shunts were clinically followed prospectively. Change in clinical state one year after shunt surgery was assessed as change on a 15-3 score NPH Grade Scale. Preoperative spinal hydrodynamics were assessed using a constant-rate lumbar infusion test. The pressure recordings were stored as raw data files and analysed retrospectively with regard to the mean cerebrospinal fluid pressure (CSFP), as well as mean CSFP wave amplitudes. Changes in NPH score 1 year after shunt surgery correlated significantly with the levels of single CSFP wave amplitudes, but not with the lumbar resistance to CSF outflow (R(out)). Mean CSFP wave amplitude was thus, in this cohort, a better predictor of clinical change one year after shunt treatment than R(out).     

Changes in intracranial pulse pressure amplitudes after shunt implantation and adjustment of shunt valve opening pressure in normal pressure hydrocephalus

Summary Background  We have previously reported that the intracranial pulse pressure amplitudes were elevated in idiopathic normal pressure hydrocephalus (NPH) patients responding to shunt surgery. Whether or not shunt implantation or adjustment of the shunt valve opening pressure modifies the intracranial pulse pressure amplitudes in NPH patients remains to be established. This report summarises our observations. Patients and methods  Thirteen patients with NPH (idiopathic in nine and secondary in four) are presented in whom continuous intracranial pressure (ICP) monitoring was done before and after shunt implantation. In two, ICP monitoring was also done during adjustment of shunt valve opening pressure. The mean ICP and mean ICP wave amplitude (i.e. pulse pressure amplitudes) were determined in 6-s time windows. Results  After shunt implantation there was a fall in both mean ICP and mean ICP wave amplitude; the reduction in the two ICP parameters correlated significantly. However, mean ICP in the supine position was normal (i.e. <15 mmHg) in 12 of 13 patients before shunt placement, and remained normal after shunting. According to our criteria, the mean ICP wave amplitudes were elevated before shunting in 12 of 13 patients and became “normalised” the day after shunting in nine patients. The reduction in mean ICP wave amplitude after shunt was highly significant at the group level. Moreover, adjustment of shunt valve opening pressure modified the levels of mean ICP wave amplitudes. Conclusions  The present observations in 13 NPH patients indicate that shunt implantation reduces mean ICP wave amplitudes. Moreover, the level of reduction can be tailored by adjustment of the shunt valve opening pressure.     

Association between intracranial pulse pressure levels and brain energy metabolism in a patient with an aneurysmal subarachnoid haemorrhage

This report addresses whether intracranial pulse pressure amplitudes are associated with brain energy metabolism, examined by intracerebral microdialysis. We present a 65-year-old female with an aneurysmal subarachnoid haemorrhage (SAH) from a left posterior communicating artery (PCOM) aneurysm. She underwent simultaneous intracranial pressure (ICP) monitoring and microdialysis (MD) as part of a diagnostic workout because of a lack of clinical improvement after long-term intensive care management. Over a 4-day period, a total of 128 samples of metabolites (glutamate, glycerol, lactate and pyruvate) were gathered, allowing retrospective comparisons with the levels of intracranial pulse pressure amplitudes (the mean ICP wave amplitude). During this 4-day period, mean ICP was normal (<15 mmHg), while mean ICP wave amplitude was high (>/=5 mmHg) in 47% of the recording time. There was a highly significant relationship between the levels of the mean ICP wave amplitude and the levels of glutamate, glycerol and lactate/pyruvate ratio. The levels of metabolites were increased when the mean ICP wave amplitude was >/=5 mmHg as compared with mean ICP wave amplitude levels <5 mmHg. We tentatively suggest that increased mean ICP wave amplitudes indicative of reduced intracranial compliance can be associated with brain ischaemia.     

Changes in the cerebrospinal fluid pulse wave spectrum associated with raised intracranial pressure

The frequency spectrum of the cerebrospinal fluid (CSF) pulse and the amplitude transfer function between arterial and CSF pressures were measured from the cisterna magna of anesthetized, artificially ventilated cats when the intracranial pressure (ICP) was raised by saline infusion. The spectrum of CSF pulsation was composed of a fundamental and three higher harmonic waves. The amplitude and the amplitude transfer function of each spectral component revealed significant positive correlation with ICP and negative correlation with cerebral perfusion pressure (CPP). Both the amplitude and the transfer function of the fundamental CSF pulse wave showed an exponential correlation with ICP and CPP. A distortion factor of the CSF pulse wave, a measure of its difference from a simple sine wave, was calculated from the spectral components. This showed that distortion of the CSF pulse wave was rapidly and progressively reduced as the ICP rose to 50 mm Hg and then was reduced less thereafter.     

The relationship of blood flow velocity fluctuations to intracranial pressure B waves.

Intracranial pressure (ICP) and continuous transcranial Doppler ultrasound signals were monitored in 20 head-injured patients and simultaneous synchronous fluctuations of middle cerebral artery (MCA) velocity and B waves of the ICP were observed. Continuous simultaneous monitoring of MCA velocity, ICP, arterial blood pressure, and expired CO2 revealed that both velocity waves and B waves occurred despite a constant CO2 concentration in ventilated patients and were usually not accompanied by fluctuations in the arterial blood pressure. Additional recordings from the extracranial carotid artery during the ICP B waves revealed similar synchronous fluctuations in the velocity of this artery, strongly supporting the hypothesis that blood flow fluctuations produce the velocity waves. The ratio between ICP wave amplitude and velocity wave amplitude was highly correlated to the ICP (r = 0.81, p less than 0.001). Velocity waves of similar characteristics and frequency, but usually of shorter duration, were observed in seven of 10 normal subjects in whom MCA velocity was recorded for 1 hour. The findings in this report strongly suggest that B waves in the ICP are a secondary effect of vasomotor waves, producing cerebral blood flow fluctuations that become amplified in the ICP tracing, in states of reduced intracranial compliance.     

Increase in the chronically monitored cerebrospinal fluid pressure after experimental brain injury in rats

The early effects of experimental brain injury with diffuse axonal lesions on intracranial pressure (ICP), mean arterial pressure (MAP) and cerebral perfusion pressure (CPP) in rats have been already studied. The aim of this experiment was to examine the effects of brain injury on ICP, MAP and CPP during the first few days post-injury. In order to do that, an accurate technique of ICP measurement had to be developed. In a series of eight rats, a translumbar intrathecal catheter (TIC) was surgically introduced allowing repeated measurements of cerebrospinal fluid pressure (CSFP). Under anaesthesia, a second series of nine rats were equipped simultaneously with TIC and an intracranial fiberoptic device to measure ICP. Simultaneous measurements of CSFP and ICP were recorded for baseline values, than during and after jugular compression which was intended to induce an acute and significant increase in ICP. A third series of 53 rats having TIC received an experimental severe brain injury. MAP was measured non-invasively and CPP was calculated as CPP MAP. CSFP, MAP and CPP were intermittently measured during 5-6 post-traumatic days and compared to the values obtained during ten control rats (SHAM). A clinical score was used to compare clinical condition. The results showed that the translumbar CSFP accurately measured ICP in rats having normal or acutely increased ICP. The experimental brain injury induced increased CSFP lasting up to 5-6 days, with increased MAP during the first 6hours. CPP values were compromised at 24-48hours. The clinical performance was reduced in the brain injured rats. The translumbar technique of CSFP measurement reflected exact ICP in normal and acutely increased ICP in rats. Experimental brain injury with diffuse axonal lesions can increase lumbar CSFP in rats for many days.     

Cerebral blood flow during plateau waves in a patient with benign intracranial hypertension--case report

A 50-year-old male presented with benign intracranial hypertension (BIH). He was admitted to our hospital for headache and papilledema. The diagnosis was BIH as continuous monitoring of lumbar cerebrospinal fluid pressure (CSFP) showed high basal pressure with intermittent plateau waves. Ten months after successful ventriculoperitoneal shunting, he presented with headache again due to shunt malfunction. CSFP monitoring showed the same findings as before. Regional cerebral blood flow (rCBF) was measured by positron emission tomography (PET) using the 15O-labeled water autoradiographic method with simultaneous recording of lumbar CSFP. The rCBF values of the cerebral cortex, white matter, thalamus, cerebellar cortex, and pons were evaluated during both the plateau waves and the intervals. In spite of severely reduced cerebral perfusion pressure, rCBF during the plateau waves was not reduced when compared with the rCBF of normal volunteers in all regions. This result might explain why patients with BIH show no impairment of consciousness or focal signs during the plateau waves.     

Intracranial pulse pressure amplitude levels determined during preoperative assessment of subjects with possible idiopathic normal pressure hydrocephalus

Summary Background. It was previously reported that the intracranial pulse pressure amplitudes were elevated in idiopathic normal pressure hydrocephalus (iNPH) patients responding to shunt surgery. In this study, pulse pressure amplitudes were determined in all patients referred for tentative iNPH, and patients were selected for shunt surgery based on the determination of their threshold levels of intracranial pulse pressure amplitudes. Patients and methods. All patients referred to our department for tentative iNPH during a 12 months time period were included. Using intracranial pressure (ICP) monitoring the intracranial pulse pressure amplitudes were determined as the mean wave amplitude in consecutive 6-seconds time windows. Intracranial pulse pressure amplitudes were defined as being elevated when the mean wave amplitudes were either ≥4 mmHg in ≥70%, ≥5 mmHg in ≥40% or ≥6 mmHg in ≥10% of the ICP recording time. Shunt treatment was offered to those with elevated mean wave amplitudes. Clinical state was assessed by using a NPH Grading Scale and the Stein-Langfitt scale before ICP monitoring, and then repeated after 12 months. Results. Among the 40 iNPH patients included during the 12 months period, the mean wave amplitudes were elevated in 24 patients (60%), while not being elevated in 16 (40%). Neither pre-operative clinical state, radiological ventricular size nor co-morbidity differed between patient groups with elevated or non-elevated mean wave amplitudes. In the shunted patients who had pre-operatively elevated mean wave amplitudes, 91% had very significant clinical change after 12 months (median change in NPH score +4). In those with non-elevated amplitudes and no shunt, clinical state was somewhat worse after 12 months (median change in NPH score −1). Conclusions. In this one-year material, mean wave amplitudes were elevated in 60% of iNPH patients. In those with elevated mean wave amplitudes who were treated with shunt, 91% had a significant clinical response.     

Effect of subarachnoid hemorrhage on intracranial pulse waves in cats

The influence of vasoconstrictors of intracranial arteries on the amplitude and configuration of the intracranial pulse wave (ICPW) was investigated. Continuous pressure recordings from the descending aorta (systemic arterial pressure) and the third cerebral ventricle (intracranial pressure) were obtained from anesthetized cats. Computerized analysis of the configuration, amplitude, and frequency spectrum of ventricular wave (ICPW) and aortic pulse wave (SAPW) was performed. Artificial cerebrospinal fluid (CSF), blood, or 5-hydroxytryptamine (5-HT) was injected intracisternally. In 24 control cats, 2 ml artificial CSF was injected into the cisterna magna. This produced a significant increase in amplitude of the ICPW but no change in the SAPW. Ten animals received 14 intracisternal injections of 2 ml autologous blood which caused narrowing of the amplitude of the ICPW as well as of all its components (P1, P2, and P3), with no significant change in the SAPW's. Eight animals were also subjected to cisternal injection of 2 ml of a 10(-4)-M solution of 5-HT, resulting in findings similar to those produced by autologous blood. Frequency spectrum of the intracranial and aortic pulse waves showed a high degree of correlation between wave amplitudes and height of the fundamental wave in the FFT record. These results suggest that the cerebral vasospasm that follows cisternal injections of blood and 5-HT in cats can be diagnosed by analysis of the ICPW. This method may allow early diagnosis and continuous monitoring of cerebral vasospasm in humans.     

The relation of intracranial pressure B-waves to different sleep stages in patients with suspected normal pressure hydrocephalus

Summary The interpretation of data from continuous monitoring of intra-cranial pressure (ICP) in patients with suspected normal pressure hydrocephalus (NPH) is the subject of controversy. Despite the fact that overnight ICP monitoring is widely used for the diagnosis of NPH, normative criteria are poorly defined. The present study demonstrates that there is a relationship between the relative frequency, the absolute amplitude, the wavelength and the morphology of B-waves and different sleep stages.Intraventricular intracranial pressure was recorded continuously overnight in 16 patients with suspected normal pressure hydrocephalus. Simultaneous polysomnography was performed to investigate the relation of spontaneous ICP oscillations to different sleep stages. A correlative analysis was done with the data of 13 patients. Three patients were excluded, one who was awake throughout the night and two in whom polysomnography was incomplete due to technicai reasons. The mean resting cerebrospinal fluid (CSF) pressure was 12.87 cm CSF. B-waves were observed in the ICP recordings of all patients. They were present for a mean of 72% of the total recording time. The relative frequency of B-waves was higher during REM sleep and sleep stage 2 as compared to wakefulness (87.8% and 83.2% vs. 56, p < 0.05). The absolute amplitude was higher during REM sleep than in wakefulness (9.56 vs. 3.44 cm CSF, p < 0.05). Wavelengths were longer in REM sleep than in wakefulness and stages 1 and 2 (62.4 vs. 42, 40.7 and 44.8 sec, p < 0.05). The morphology of B-waves was also related to different sleep stages. Ramp-type B-waves were associated with REM sleep in six patients, however, were also present in sleep stage 2 in three of them.Knowledge of the relation of spontaneous ICP oscillations to different sleep stages may help to establish physiological foundations and alterations. Furthermore, polysomnography may be useful to avoid erroneous interpretation of ICP recordings due to sleep stage related variability.     

The effect of increased intracranial pressure during the appearance of pressure waves on the brainstem.

The effects of increased intracranial pressure (ICP) during the appearance of plateau waves or B-waves to the brainstem functions were investigated by evaluation of evoked potentials. The ICP and systemic blood pressure were continuously recorded in nine cases of intracranial hypertension. In the four cases demonstrating plateau waves in ICP recording, the latencies of the auditory brainstem evoked potentials (ABEP) measured during the appearance of plateau waves showed no significant differences compared to those measured during the interval phase between two plateau waves. In the five cases demonstrating B-waves in ICP recording, four cases showed significant (p less than 0.05) prolongation of the V wave of ABEP and three showed significant (p less than 0.05) prolongation of the P15 of somatosensory evoked potentials during the phase of increased ICP level with B-waves compared to those measured during the phase of decreased ICP level without B-waves, produced by external drainage of the cerebrospinal fluid or mannitol administration. The results indicated that during the appearance of plateau waves there were no significant changes of electrical activity in the brainstem, even though there was a significant reduction in cerebral perfusion pressure. It is suggested that in cases with the appearance of B-waves, an increase in ICP frequently affects the electrical activity in the brainstem.     

A computer system for the identification of the cerebrospinal compensatory model

Summary A computer system, based on IBM PC, was designed for the cerebrospinal compensatory model identification. The intracranial pressure (ICP) signal, registered during the lumbo-lumbar infusion test is analyzed by means of the spectral analysis algorithm in order to measure precisely the pulse wave amplitude. The amplitude and the mean ICP level, calculated repetetively within the period of about 8 seconds, are stored on the disk and form the basis for further model identification. Three different methods of identification were applied. They enable one to estimate the fundamental model parameters, such as: resistance to the cerebrospinal fluid resorption, pressure-volume index, baseline pressure, rate of formation of the cerebrospinal fluid.Statistical evaluation of the results of the infusion test analysis obtained by means of the system described in two groups of hydrocephalic patients (children and adults) is presented.     

Monitoring of cerebrospinal dynamics using continuous analysis of intracranial pressure and cerebral perfusion pressure in head injury

Summary Cerebrospinal dynamics has been investigated by statistical analysis of results of computerised monitoring of 80 head injured patients admitted to the Intensive Care Unit at Pinderfields General Hospital. One minute average values of intracranial pressure (ICP), systemic arterial pressure (ABP), cerebral perfusion pressure (CPP), amplitude of the fundamental component of the intracranial pressure pulse wave and the short-term moving correlation coefficient between that amplitude and mean ICP (RAP) were recorded. It was found that reduction of CPP down to 40mmHg was more often caused by decrease in ABP than increase in ICP. Further falls in CPP below 40mmHg were caused by substantial increases in ICP above 25 mmHg. The relationship between the ICP pulse wave amplitude and CPP showed a significant gradual increase in amplitude with CPP decreasing from 75 to 30 mmHg. For CPP below 30 mmHg there is a sharp decrease in amplitude followed by a change in the coefficient RAP from positive to negative values. This was interpreted as a sign of critical disturbance in cerebral circulation.     

Two computerized methods used to analyze intracranial pressure B waves: comparison with traditional visual interpretation

OBJECT: Slow and rhythmic oscillations in intracranial pressure (ICP), also known as B waves, have been claimed to be one of the best preoperative predictive factors in idiopathic adult hydrocephalus syndrome (IAHS). Definitions of B waves vary widely, and previously reported results must be treated with caution. The aims of the present study were to develop a definition of B waves, to develop a method to estimate the B-wave content in an ICP recording by using computer algorithms, and to validate these procedures by comparison with the traditional visual interpretation. METHODS: In eight patients with IAHS, ICP was continuously monitored for approximately 20 hours. The ICP B-wave activity as a percentage of total monitoring time (B%) was estimated by using visual estimation according to the definition given by Lundberg, and also by using two computer algorithms (Methods I and II). In Method I each individual wave was classified as a B wave or not, whereas Method II was used to estimate the B-wave content by evaluating the B-wave power in 10-minute blocks of ICP recordings. CONCLUSIONS: The two computerized algorithms produced similar results. However, with the amplitude set to 1 mm Hg, Method I yielded the highest correlation with the visual analysis (r = 0.74). At least 5 hours of monitoring time was needed for an acceptable approximation of the B% in an overnight ICP recording. The advantages of using modern technology in the analysis of B-wave content of ICP are obvious and these methods should be used in future studies.     

Hemodynamic characterization of intracranial pressure plateau waves in head-injury patients.

OBJECT: Plateau waves of intracranial pressure (ICP) are often recorded during intensive care monitoring of severely head injured patients. They are traditionally interpreted as meaningful secondary brain insults because of the dramatic decrease in cerebral perfusion pressure (CPP). The aim of this study was to investigate both the hemodynamic profile and the clinical consequences of plateau waves. METHODS: One hundred sixty head-injured patients were studied using continuous monitoring of ICP; almost 20% of these patients exhibited plateau waves. In 96 patients arterial pressure, ICP, and transcranial Doppler (TCD) blood flow velocity were studied daily for 20 minutes to 3 hours. Sixteen episodes of plateau waves in eight patients were recorded and analyzed. The dramatic increase in ICP was followed by a profound fall in CPP (by 45%). In contrast, flow velocity fell by only 20%. Autoregulation was documented to be intact both before and after plateau but was disturbed during the wave (p < 0.05). Pressure-volume compensatory reserve was always depleted before the wave. Cerebrovascular resistance decreased during the wave by 60% (p < 0.05) and TCD pulsatility increased (p < 0.05). Plateau waves did not increase the probability of an unfavorable outcome following injury. CONCLUSIONS: The authors have confirmed that the plateau waves are a hemodynamic phenomenon associated with cerebrovascular vasodilation. They are observed in patients with preserved cerebral autoregulation but reduced pressure-volume compensatory reserve.     

Cerebrospinal fluid pressure in patients with brain tumors: impact of fentanyl versus alfentanil during nitrous oxide-oxygen anesthesia

The effects on the cerebrospinal fluid pressure (CSFP) of alfentanil and fentanyl were compared during nitrous oxide-oxygen (N2O-O2) anesthesia in 24 patients who had brain tumors. Monitored variables included CSFP (lumbar subarachnoid catheter), heart rate from electrocardiographic lead II, mean radial arterial blood pressure, and arterial blood gas tensions. General anesthesia was induced with thiopental, 5 mg/kg IV in divided doses, and maintained with 70% N2O in O2; ventilation was held constant (PaCO2 = 37.4 +/- 1.6 mm Hg [mean +/- SEM]). After baseline data were recorded, 16 subjects were randomly assigned to receive either 5 micrograms/kg fentanyl as an intravenous bolus or 50 micrograms/kg alfentanil as an intravenous bolus, followed by an infusion of alfentanil at 1 micrograms.kg-1.min-1. Monitored variables were continuously recorded for 15 min after opioid injection. A third group of 8 patients was studied subsequently; they received only N2O-O2 during a 15-min observation period and served as controls. Blood pressure was held constant with an intravenous infusion of 0.1% phenylephrine, as needed; noxious stimulation was carefully avoided. Cerebrospinal fluid pressure remained unchanged both in patients who received N2O-O2 alone and in those who received fentanyl-N2O-O2. By contrast, those who received alfentanil-N2O-O2 had a gradual increase in CSFP, reaching 30% above baseline values after 10 min and stabilizing thereafter. Although the absolute increase in CSFP during normocarbic alfentanil-N2O anesthesia was relatively small (9.5 +/- 1.3 mm Hg to 13.0 +/- 1.3 mm Hg [mean +/- SE], P less than 0.05), the absence of a similar effect after fentanyl administration suggests that precautionary measures such as hyperventilation are advisable if alfentanil is used for potentiating normocarbic N2O-O2 anesthesia in neurosurgical patients with intracranial mass lesions.     

Mivacurium in patients with intracranial pathology

BACKGROUND: The aim of this study was to evaluate the effects of mivacurium on the cerebrospinal fluid pressure (CSFP) in patients requiring muscle relaxation to facilitate mechanical ventilation and on the intracranial pressure (ICP) in patients undergoing neurosurgery. METHODS: Experimental design: prospective study. Setting: ICU in a hospital and operating room in a neurosurgery department at University. PATIENTS: 12 patients, GCS 6-7, with a mean age of 62.6 +/- 6.2 were studied in ICU and 10 patients, ASA I-II, with a mean age of 58.6 +/- 6.4 were studied in the operating room. INTERVENTIONS: all patients received mivacurium as single bolus dose of 0.2 mg/kg i.v. MEASUREMENTS: Heart rate, SAP, DAP and MAP were recorded at different times. In ICU CSFP was measured via a catheter in lumbar subarachnoid space and in operating room ICP was measured via an intraventricular catheter. CPP was evaluated as the difference between MAP and ICP. Statistical analysis was carried out using ANOVA for repeated measures and Bonferroni "t"-test and a value of p < 0.05 was considered to be significant. RESULTS: Mivacurium was found not to influence or to increase ICP or CSFP. No significant changes in cardiocirculatory parameters were recorded in all patients. CONCLUSIONS: In conclusion, mivacurium can be considered a suitable and manageable neuromuscular blocking drug in the management of patients with intracranial pathology.     

Analysis of intracranial pressure waveform during infusion test

Summary An analysis of intracranial pressure (ICP), based on an examination of the temporary correlation between the changes in amplitude of the pulse wave and the mean ICP level, is presented. The paper contains a discussion of the preliminary results of the method when applied to the analysis of ICP as monitored during infusion tests in a group of 24 children. Infusion of a certain volume of CSF is a good example of an uncompensated volume process, introduced externally into the intracranial space. Results allow an interpretation of the short term correlation coefficient RAP (correlation coefficient between ICP and variations of the amplitude of fundamental component of the pulse wave AMP), as a steady state index. According to this interpretation, the presented analysis enables the observation of a loss of equilibrium during the test. Other phenomena can also be observed, for instance a recovery to equilibrium after the test, nonlinearities of amplitude-pressure relationship, vasomotor reflexes etc.     

Analysis of the cerebrospinal fluid pulse wave in intracranial pressure

The configuration of the intracranial pressure (ICP) pulse wave represents a complex sum of various components. Amplitude variations of an isolated component might reflect changes in a specific intracranial structure. Fifteen awake patients suffering from hydrocephalus, benign intracranial hypertension, or head injury underwent ICP monitoring through a ventricular catheter and were subjected to three standardized maneuvers to alter the intracranial dynamics: head elevation, voluntary hyperventilation, and cerebrospinal fluid (CSF) withdrawal. A 12 degrees head elevation and fractionated CSF withdrawal caused a mild ICP drop and a proportionate amplitude reduction of all the wave components. Voluntary hyperventilation caused a comparable fall in ICP, and a disproportionate reduction in the amplitude of the wave components, especially the P2 component. It is postulated that the decrease in amplitude of the P2 component reflects the reduction of the cerebral bulk caused by hyperventilation. Head elevation and CSF withdrawal caused a decrease of global ICP but no specific changes in any intracranial structure, and consequently the configuration of the pulse wave remained unchanged. The establishment of relationships between anatomical substrate and particular wave components is promising since potentially it could be useful for monitoring conditions such as vasoparalysis, impaired cerebrovascular reactivity, and cerebral edema.