Intracranial Pressure Wave Amplitude Research Articles

A dynamic nonlinear relationship between the static and pulsatile components of intracranial pressure in patients with subarachnoid hemorrhage

In the search for optimal monitoring and predictive tools in neurocritical care, the relationship of the pulsatile component of intracranial pressure (ICP) and the pressure itself has long been of great interest. Higher pressure often correlates with a higher pulsatile response to the heartbeat, interpreted as a type of compliance curve. Various mathematical approaches have been used, but regardless of the formula used, it is implicitly assumed that a reproducible curve exists. The authors investigated the stability of the correlation between static and pulsatile ICPs in patients with subarachnoid hemorrhage (SAH) who were observed for several hours by using data sets large enough to allow such calculations to be made. The ICP recordings were obtained in 39 patients with SAH and were parsed into 6-second time windows (1,998,944 windows in 197 recordings). The ICP parameters were computed for each window as follows: static ICP was defined as the mean ICP, and pulsatile ICP was characterized by mean ICP wave amplitude, rise time, and rise time coefficient. The mean ICP and ICP wave amplitudes were simultaneously high or low (the expected correlation) in only approximately 60% of observations. Furthermore, static and pulsatile ICP correlated well only over short intervals; the degree of correlation weakened over periods of hours and was inconsistent across patients and within individual patients over time. Decorrelation originated with abrupt shifting and gradual drifting of mean ICP and ICP wave amplitude over several hours. The relationship between the static and pulsatile components of ICPs changes over time. It evolves, even in individual patients, over a number of hours. This can be one reason the observation of high pulsatile ICP (indicative of reduced intracranial compliance) despite normal mean ICP that is seen in some patients with SAH. The meaning and potential clinical usefulness of such changes in the curves is uncertain, but it implies that clinical events result not only from moving further out on a compliance curve; in practice, the curve, and the biological system that underlies the curve, may itself change.

Cerebrospinal fluid pulse pressure amplitude during lumbar infusion in idiopathic normal pressure hydrocephalus can predict response to shunting

BackgroundWe have previously seen that idiopathic normal pressure hydrocephalus (iNPH) patients having elevated intracranial pressure (ICP) pulse amplitude consistently respond to shunt surgery. In this study we explored how the cerebrospinal fluid pressure (CSFP) pulse amplitude determined during lumbar infusion testing, correlates with ICP pulse amplitude determined during over-night ICP monitoring and with response to shunt surgery. Our goal was to establish a more reliable screening procedure for selecting iNPH patients for shunt surgery using lumbar intrathecal infusion.MethodsThe study population consisted of all iNPH patients undergoing both diagnostic lumbar infusion testing and continuous over-night ICP monitoring during the period 2002-2007. The severity of iNPH was assessed using our NPH grading scale before surgery and 12 months after shunting. The CSFP pulse was characterized from the amplitude of single pressure waves.ResultsTotally 62 iNPH patients were included, 45 of them underwent shunt surgery, in whom 78% were shunt responders. Among the 45 shunted patients, resistance to CSF outflow (Rout) was elevated (≥ 12 mmHg/ml/min) in 44. The ICP pulse amplitude recorded over-night was elevated (i.e. mean ICP wave amplitude ≥ 4 mmHg) in 68% of patients; 92% of these were shunt responders. In those with elevated overnight ICP pulse amplitude, we found also elevated CSFP pulse amplitude recorded during lumbar infusion testing, both during the opening phase following lumbar puncture and during a standardized period of lumbar infusion (15 ml Ringer over 10 min). The clinical response to shunting after 1 year strongly associated with the over-night ICP pulse amplitude, and also with the pulsatile CSFP during the period of lumbar infusion. Elevated CSFP pulse amplitude during lumbar infusion thus predicted shunt response with sensitivity of 88 and specificity of 60 (positive and negative predictive values of 89 and 60, respectively).ConclusionsIn iNPH patients, shunt response can be anticipated in 9/10 patients with elevated overnight ICP pulse amplitude, while in only 1/10 with low ICP pulse amplitude. Additionally, the CSFP pulse amplitude during lumbar infusion testing was elevated in patients with elevated over-night ICP pulse amplitude. In particular, measurement of CSFP pulse amplitude during a standardized infusion of 15 ml Ringer over 10 min was useful in predicting response to shunt surgery and can be used as a screening procedure for selection of iNPH patients for shunting.

Diagnostic Intracranial Pressure Monitoring and Surgical Management in Idiopathic Normal Pressure Hydrocephalus

To review our experience of managing idiopathic normal pressure hydrocephalus (iNPH) during the 6-year period from 2002 to 2007, when intracranial pressure (ICP) monitoring was part of the diagnostic workup. The review includes all iNPH patients undergoing diagnostic ICP monitoring during the years 2002 to 2007. Clinical grading was done prospectively using a normal pressure hydrocephalus (NPH) grading scale (scores from 3 to 15). The selection of patients for surgery was based on clinical symptoms, enlarged cerebral ventricles, and findings on ICP monitoring. The median follow-up time was 2 years (range, 0.3-6 years). Both static ICP and pulsatile ICP were analyzed. A total of 214 patients underwent the diagnostic workup, of whom 131 went on to surgery. Although 1 patient died shortly after treatment, 103 of the 130 patients (79%) improved clinically. This improvement lasted throughout the observation period. The static ICP observed during ICP monitoring was a poor predictor of the response to surgery. In contrast, among 109 of 130 patients with increased ICP pulsatility (ie, ICP wave amplitude >4 mm Hg on average and >5 mm Hg in >10% of recording time), 101 (93%) were responders (ie, increase in the NPH score of >2). Correspondingly, only 2 of 21 (10%) without increased ICP pulsatility were responders. Superficial wound infection was the only complication of ICP monitoring and occurred in 4 (2%) patients. Surgical results in iNPH were good with almost 80% of patients improving after treatment. The data indicate that improvement after surgery can be anticipated in 9 of 10 iNPH patients with abnormal ICP pulsatility, but in only 1 of 10 with normal ICP pulsatility. Diagnostic ICP monitoring had a low complication rate.

Cerebral microdialysis and intracranial pressure monitoring in patients with idiopathic normal-pressure hydrocephalus: association with clinical response to extended lumbar drainage and shunt surgery

This study was performed in patients with idiopathic normal-pressure hydrocephalus (iNPH) to monitor cerebral metabolism with microdialysis (MD) and intracranial pressure (ICP) readings, and relate to the clinical responses to extended lumbar drainage (ELD) and shunt surgery. The baseline levels of MD metabolites and ICP were monitored overnight in 40 consecutive patients with iNPH. In a subset of 28 patients, monitoring was continued during 3 days of ELD. Thirty-one patients received a ventriculoperitoneal shunt. The clinical severity of iNPH was determined before and then 3 and 6-12 months after shunt surgery. Altered levels of MD markers (lactate, pyruvate, lactate/pyruvate ratio, glutamate, and/or glycerol) were seen in all patients at baseline; these improved during ELD. Despite normal static ICP (mean ICP), the pulsatile ICP (the ICP wave amplitude) was increased in 24 patients (60%). Only the level of the ICP wave amplitude differentiated the ELD and/or shunt responders from nonresponders. The MD monitoring indicated low-grade cerebral ischemia in patients with iNPH; during ELD, cerebral metabolism improved. The pulsatile ICP (the ICP wave amplitude) was the only variable differentiating the clinical responders from the nonresponders. The authors suggest that the pulsatile ICP reflects the intracranial compliance and that CSF diversion improves the biophysical milieu of the nerve cells, which subsequently may improve their biochemical milieu.

Impact of sampling rate for time domain analysis of continuous intracranial pressure (ICP) signals

Time domain analysis of the intracranial pressure (ICP) waveform is critically dependent on the exact reproduction of the ICP waveform. This study explored how the sampling rate of the ICP signal affects the time domain analysis. It was also assessed through this study how upsampling (interpolation) improves the time domain analysis. From the hospital database, a set of 55 ICP waveforms were retrieved from 48 patients (28 children and 20 adults). First, the ICP signals originally sampled at 200 or 100 Hz were compared with the ICP signals downsampled to 5, 10, 20, 25, 50 Hz (and 100 Hz). Second, the original ICP signals were compared with ICP signals upsampled (i.e. interpolated) to 100 Hz (from 5, 10, 20, 25 or 50 Hz). For each ICP recording the output of time domain analysis was the average value and the quantitative distribution of mean ICP wave amplitudes determined every six second (6 s) time window. The total material incorporated a total of 373,371 6 s time windows. Downsampling revealed that the time domain analysis could be most faithfully applied to ICP signals sampled at 50 Hz or above, while ICP signals sampled at 25 Hz deviated more from the original signal than we would accept from a clinical perspective. The use of interpolation gave better representation of the peaks, and should be applied to all ICP signals sampled at lower rate than 100 Hz.

Demonstration of uneven distribution of intracranial pulsatility in hydrocephalus patients

Data from intracranial pressure (ICP) recordings in patients with hydrocephalus were reviewed to determine whether intracranial pulsatility within the cerebrospinal fluid (CSF) of cerebral ventricles (ICP(LV)) may differ from that within the brain parenchyma (ICP(PAR)), and whether pulsatility may differ between noncommunicating ventricles. The authors retrieved data from recordings previously obtained in 7 patients with hydrocephalus (noncommunicating in 4 and communicating in 3) and shunt failure who received both an external ventricular drainage (EVD) and an ICP sensor as part of surveillance during intensive care. Simultaneous ICP(LV) and ICP(PAR) signals were available in 6 cases, and simultaneous signals from the lateral and fourth ventricles (ICP(LV) and ICP4V, respectively) were recorded in 1 case. The recordings with both signals were parsed into 6-second time windows. Pulsatility was characterized by the wave amplitude and rise time coefficient, and differences in pulsatility between the ICP(LV) and ICP(PAR) signals (6 cases) or ICP(LV) and ICP4V signals (1 case) were determined. There was uneven distribution of intracranial pulsatility in all 7 patients, shown as significantly elevated pulsatility (that is, higher wave amplitudes and rise time coefficients) within the ventricles (ICP(LV)) than within brain parenchyma (ICP(PAR)) in 6 patients, and significantly higher pulsatility in the fourth (ICP4V) than in the lateral (ICP(LV)) ventricles in 1 patient. Differences > or = 1 mm Hg in ICP wave amplitude were found in 0.5-100% (median 9.4%) of observations in the 7 patients (total number of 6-second time windows, 68,242). The present observations demonstrate uneven distribution of intracranial pulsatility in patients with hydrocephalus, higher pulse pressure amplitudes within the ventricular CSF (ICP(LV)) than within the brain parenchyma (ICP(PAR)). This may be one mechanism behind ventricular enlargement in hydrocephalus.

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

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. 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. 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. 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.

Rapid and severe rise in static and pulsatile intracranial pressures during a generalized epileptic seizure

In a patient with no prior history of seizures we were able to record static (mean) intracranial pressure (ICP) and pulsatile ICP (mean ICP wave amplitude) continuously during a first-time generalized epileptic seizure. The patient experienced episodic headache five months after a subarachnoid haemorrhage. In order to rule out low-pressure hydrocephalus she was admitted for a 24-hour intracranial pressure registration. ICP parameters were normal prior to the seizure. We observed an immediate and enormous rise in both static (mean) ICP and pulsatile ICP (mean ICP wave amplitude). Mean ICP and ICP wave amplitude peaked at 93 mmHg and 22 mmHg, respectively. Pulsatile ICP remained elevated after normalization of static ICP and may indicate impairment of intracranial compliance even after the static ICP was normalized.

Association among intracranial compliance, intracranial pulse pressure amplitude and intracranial pressure in patients with intracranial bleeds

Objective: To investigate the association among intracranial compliance (ICC), intracranial pulse pressure amplitude and intracranial pressure (ICP) in patients with intracranial bleeds.Methods: Five patients with intracranial bleeds had their ICC and ICP monitored during days 1–8 after ictus. The recordings were stored as raw data files and analysed retrospectively. The parameters mean ICC, mean ICP wave amplitude and mean ICP were determined and average values were calculated in 1 hour time periods.Results: A total of 2621 hour recordings were analysed. There was a significant correlation between mean ICC and mean ICP wave amplitude and between mean ICC and mean ICP. The mean ICP wave amplitude was significantly higher during the 1 hour periods with mean ICC<0.5 ml/mmHg and significantly lower during 1 hour periods with mean ICC 1.5–3.0 ml/mmHg. Correspondingly, in the 1591 hour recordings with mean ICP wave amplitude≥5.0 mmHg, mean ICC was significantly lower than in the 103 recordings with mean ICP wave amplitude<5.0 mmHg. Mean ICP was normal (i.e. <20 mmHg) in 260 of 262 (99.2%) of the 1 hour recordings; in the 491 hour recordings with mean ICP>15 mmHg, mean ICC was significantly lower than in the 213 recordings with mean ICP<15.0 mmHg.Conclusion: In this cohort of pressure recordings, there was a strong association between ICC and intracranial pulse pressure amplitude. There also was a strong association between ICC and mean ICP, but mean ICP was normal in 260 of 2621 hour recordings (99.2%).

Is Intracranial Pressure Waveform Analysis Useful in the Management of Pediatric Neurosurgical Patients?

Background: We have reported casuistic observations that intracranial pressure (ICP) waveform analysis may be useful in the management of pediatric patients. Method: We here report our whole patient material of 65 children undergoing ICP monitoring with storage of their ICP raw data files during the years 2002–2005. We retrospectively explored the clinical symptoms/findings and radiological cerebral ventricular size before ICP monitoring. Mean ICP was the actively treated ICP parameter. Using an algorithm for identification of cardiac-beat-induced pressure waves we retrospectively determined the mean ICP wave amplitude and latency, in addition to mean ICP. Outcome with regard to change in symptoms/findings during a 1-year period was determined in 55 children. Results: The material includes children with hydrocephalus, craniosynostosis, shunt failure, benign intracranial hypertension and others. The ICP recordings gave wrong diagnostic information due to bad signal quality in 5 of 65 patients (7.7%). The mean ICP wave amplitude was increased in those with papilledema, lethargy and nausea. The main observations were that the mean ICP wave amplitude (not mean ICP) was increased in those that improved from clinical symptoms/findings after treatment and in those that were unchanged/worse after not being treated. Conclusions: Waveform analysis with computation of the mean ICP wave amplitude was more useful by providing information about the quality of the ICP recording, by comparing better with the symptoms/findings at the time of ICP monitoring and by best predicting outcome. Most significantly, 14 of 55 patients (25%) with high amplitudes and left untreated did not recover spontaneously.

Association between intracranial, arterial pulse pressure amplitudes and cerebral autoregulation in head injury patients

Objective: To explore whether intracranial pulse pressure amplitudes relate to arterial pulse pressure amplitudes and whether correlations between time-related changes in intracranial and arterial pulse pressure amplitudes associate with indices of cerebral autoregulation.Methods: A total of 257 continuous and simultaneous intracranial pressure (ICP), arterial blood pressure (ABP) and middle cerebral artery (MCA) blood velocity recordings were obtained 1–14 days after ictus in 76 traumatic head injury patients and analysed retrospectively. Clinical outcome was assessed using the Glasgow outcome scale (GOS). Pulse pressure amplitudes of corresponding single ICP and ABP waves were correlated in consecutive 200 wave pairs. Mean ICP, mean ABP and mean ICP wave amplitudes, and mean and systolic MCA blood flow velocities, were computed in consecutive 6 second time windows. The indices of cerebral autoregulation PRx (moving correlation between mean ICP and mean ABP), and Mx and Sx (moving correlation between mean and systolic MCA blood velocity and cerebral perfusion pressure) were calculated over 4 minute periods and averaged over each recording.Results: Intracranial pulse pressure amplitudes were not related to arterial pulse pressure amplitudes (mean of Pearson's correlations coefficients: 0.04). Outcome was related to mean ICP, PRx and Sx (p ≤ 0.04, multiple regression analysis). Correlations between intracranial and arterial pulse pressure amplitudes were weakly related to PRx (Pearson's correlation coefficient: 0.16; p=0.01), but were not related to the indices of cerebral autoregulation Mx (Pearson's correlation coefficient: 0.07) and Sx (Pearson's correlation coefficient: 0.04).Conclusions: In this cohort of pressure recordings, we found no evidence of a correlation between intracranial and arterial blood pressure amplitudes. The correlation appeared not to be related to the state of cerebral autoregulation, although a weak correlation was found with pressure reactivity index PRx.

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.

From intracranial pressure to intracranial pressure wave‐guided intensive care management of a patient with an aneurysmal subarachnoid haemorrhage

We report on a 65-year-old female with an aneurysmal subarachnoid hemorrhage (SAH) that was followed clinically, radiologically and electrophysiologically before and after converting from intracranial pressure (ICP)-guided to ICP wave-guided intensive care management. Intracranial pressure-guided management is aimed at keeping mean ICP < 15-20 mmHg, while ICP wave-guided management is aimed at keeping mean ICP wave amplitude < 5 mmHg. The aims of management were obtained by adjusting cerebrospinal fluid (CSF) draining volume from her external ventricular drain. No improvement was seen clinically or in cerebral magnetic resonance imaging (MRI) scans during the ICP-guided management. Clinical, MRI and neurophysiologic (electroencephalography and auditory evoked responses) improvements were obvious within 2 days after converting from ICP- to ICP wave-guided management. This case report describes how we used various ICP parameters to guide intensive care management of an aneurysmal SAH patient.

Comparison of simultaneous continuous intracranial pressure (ICP) signals from ICP sensors placed within the brain parenchyma and the epidural space

Simultaneous continuous intracranial pressure (ICP) signals from two different ICP sensors (Codman ICP MicroSensor; Johnson & Johnson, Raynham, MA) placed within the brain parenchyma and the epidural space were compared in ten patients with idiopathic normal pressure hydrocephalus (iNPH). Comparisons were made at the single ICP wave level by determining differences in mean pressure, and pulse pressure amplitude (dP) and latency (dT, i.e. rise time). Differences for the parameters mean ICP, mean ICP wave amplitude and mean ICP wave latency were also determined during consecutive 6-s time windows. The ICP sensors located within the brain parenchyma and epidural space showed marked differences in mean pressure. On the contrary, there were minor differences between sensors in 8 of 10 patients regarding single wave pulse pressure amplitude (dP) and single wave latency (dT, i.e. rise time), and also with regard to the parameters mean ICP wave amplitude and mean ICP wave latency. The levels of mean ICP wave amplitude s used for predicting shunt response in iNPH patients were independent of sensor location in 9 of 10 patients. These results extend previous data that epidural ICP monitoring cannot be used to reliably determine mean ICP, however, epidural ICP monitoring is very useful for determining ICP waveform parameters such as pulse pressure amplitude (dP) and mean ICP wave amplitude. It is suggested that epidural ICP monitoring with determination of mean ICP wave amplitude can be used to predict shunt response in iNPH, though an ICP sensor designed for epidural ICP monitoring would be preferable.

Intracranial pressure levels and single wave amplitudes, Glasgow Coma Score and Glasgow Outcome Score after subarachnoid haemorrhage

To relate intracranial pressure (ICP) levels and single ICP wave amplitudes to the acute clinical state (Glasgow Coma Score, GCS) and final clinical outcome (Glasgow Outcome Score, GOS) in patients with subarachnoid haemorrhage (SAH). Twenty-seven consecutive patients with severe SAH had their ICP and arterial blood pressure (ABP) continuously monitored during days 1-6 after SAH. The acute clinical state could be assessed in 11 non-sedated cases using the Glasgow Coma Scale, while outcome was assessed in all cases after 6 months using the Glasgow Outcome Scale. The ICP/ABP recordings were stored as raw data files and analyzed retrospectively. For every consecutive 6 seconds time window, mean ICP, mean cerebral perfusion pressure (CPP) and the mean ICP wave amplitude were computed. The GCS during days 1-6 after SAH was significantly related to the mean ICP wave amplitude, but not to the mean ICP or mean CPP. There was also a strong relationship between the mean ICP wave amplitude and GOS 6 months after SAH, with mean ICP wave amplitudes being significantly lower in those with moderate disability/good recovery, as compared with those with severe disability and death. Mean ICP was significantly higher in those who died than in the group with moderate disability/good recovery whereas mean CPP was not different between outcome groups. In this small patient group the mean ICP wave amplitude during days 1-6 after SAH was related to the acute clinical state (GCS) as well as to the clinical outcome (GOS) 6 months after SAH. Similar relationships were not found for mean ICP or the mean CPP, except for a higher mean ICP in those who died than in those with moderate disability/good recovery.

Intracranial Pressure Parameters in Idiopathic Normal Pressure Hydrocephalus Patients with or without Improvement of Cognitive Function after Shunt Treatment

Background/Aims: Previous research has shown improvements in the clinical triad (gait, incontinence and cognitive dysfunction) after shunt surgery in idiopathic normal pressure hydrocephalus (iNPH) patients with intracranial pulse pressure amplitudes >4–5 mm Hg, the pulse amplitudes being <4 mm Hg in the nonresponders. However, it is unknown whether similar differences exist regarding change in cognitive functioning after shunt surgery. The aim of this study was to compare preoperative intracranial pressure (ICP) parameters between iNPH that either improved or not improved in cognitive function after shunt treatment. Methods: Neuropsychological testing was performed before and after surgery in 27 consecutive iNPH patients treated with ventriculoperitoneal shunts. The ICP recordings were performed as part of routine preoperative assessment, stored as raw data files, and analyzed retrospectively. The mean ICP as well as single ICP wave amplitudes were computed and analyzed in consecutive 6-second time windows. Results: Significant improvement in neuropsychological tests, defined as a 4-point improvement in Folstein Mini-Mental State Examination or improvement by one standard deviation in 50% of subtests of Dementia Rating Scale, was found in 12 patients (44%; shunt responders). In these patients, mean ICP was similar though the mean ICP wave amplitude was significantly higher than in the shunt nonresponders. Conclusions: While preoperative mean ICP was similar, the mean ICP wave amplitudes were considerably higher in iNPH patients with significant change in cognitive function following shunt surgery.

Lumbar cerebrospinal fluid pressure waves versus intracranial pressure waves in idiopathic normal pressure hydrocephalus

The aim of this study was to explore how the lumbar cerebrospinal fluid pressure (CSFP) waves recorded during lumbar infusion compared with the intracranial pressure (ICP) waves recorded, either during lumbar infusion or during long-term, overnight monitoring. For this purpose, we assessed 27 simultaneous lumbar CSFP/ICP recordings made during lumbar infusion and 27 long-term, overnight ICP recordings in 27 consecutive idiopathic normal pressure hydrocephalus (iNPH) patients. Pressure waves during lumbar infusion were explored by computing pulse pressure amplitude and mean single wave pressure of every corresponding CSFP/ICP wave pair; among our 27 lumbar CSFP/ICP recordings a total of 35,532 CSFP/ICP wave pairs were available for analysis. We as well computed mean values of pulse pressure amplitude (i.e. mean CSFP wave amplitude or mean ICP wave amplitude) and mean values of mean single wave pressure (i.e. mean CSFP or mean ICP) during consecutive 6-s time windows, as well as average values for the individual recordings. During lumbar infusion, the cerebrospinal fluid pulse pressure amplitudes were about 2 mmHg smaller than the corresponding intracranial pulse pressure amplitudes. The mean CSFP wave amplitudes recorded during lumbar infusion correlated significantly with the mean ICP wave amplitudes recorded either during lumbar infusion or during long-term, overnight ICP monitoring. In 21 of 27 lumbar infusion tests (78%), the presence of elevated lumbar mean CSFP waves was related to presence of elevated mean ICP wave amplitudes during long-term, overnight ICP monitoring. Hence, the lumbar cerebrospinal fluid pulse pressure amplitudes recorded during lumbar infusion could be used to predict the intracranial pulse pressure amplitudes recorded during long-term, overnight ICP monitoring.

Intracranial pressure parameters in idiopathic normal pressure hydrocephalus patients treated with ventriculo-peritoneal shunts

Although the mean intracranial pressure (ICP) is normal in patients with idiopathic normal pressure hydrocephalus (iNPH), there could possibly be alterations in their single ICP waves. Thirty-nine consecutive patients treated for iNPH with ventriculo-peritoneal shunts were followed prospectively with regard to clinical and radiological findings. Changes in clinical state 12 months after shunt surgery were assessed as change on a 15-3 score NPH Grading Scale, while the changes in ventricular size were assessed by linear measures. The ICP recordings were performed as part of routine pre-operative assessment, stored as raw data files, and analyzed retrospectively. The mean ICP as well as single ICP wave amplitudes were computed and analysed in consecutive 6 second time windows. Twelve months after shunt surgery, changes in NPH score of 5 or more (very significant improvement) were observed in 12 patients (31%), of 3 to 4 (significant improvement) in 6 patients (15%), of 1 to 2 (slight improvement) in 9 patients (23%) and of -4 to 0 (non-responders) in 12 patients (31%). The ventricular size did not change in any of the outcome categories. While the pre-operative mean ICP was similar between outcome groups, the mean ICP wave amplitude was significantly higher in patients improving clinically as compared to the non-responders. While pre-operative mean ICP was similar, the mean ICP wave amplitudes were significantly higher in iNPH patients improving clinically after shunt treatment as compared to the non-responders.

A new method for processing of continuous intracranial pressure signals

This paper describes a new method for processing of continuous pressure signals. Continuous intracranial pressure (ICP) signals were sampled at 100 Hz, converted into digital data and processed during 6 s time windows. According to a new algorithm, cardiac beat-induced single ICP waves were identified; pressure waves caused by noise in the signal were rejected for further analysis. The amplitude and latency values of the accepted single ICP waves were determined. For accepted 6 s time windows, the mean ICP wave was computed as mean ICP wave amplitude and mean ICP wave latency. Mean ICP for every time window was computed according to current practice as sum of pressure levels divided by number of samples. The mean ICP wave parameters provide information about the single ICP waves that is not given by mean ICP. The method has been implemented in software to be used during online ICP monitoring, revealing mean ICP wave amplitude, mean ICP wave latency and mean ICP as numerical values every 6 s. The values are presented in trend plots. Verification of correct single ICP wave identification can be done during online ICP monitoring. The clinical significance of the method was illustrated in four patients by observations that mean wave amplitudes corresponded better to the acute clinical state than the mean ICP; mean wave amplitudes could be elevated despite a normal mean ICP. In one patient with ICP and arterial blood pressure (ABP) signals monitored simultaneously with identical time reference, there was a weak correlation between mean ICP and ABP wave amplitudes. It is tentatively suggested that the mean ICP wave parameters are related to intracranial pressure–volume compensatory reserve capacity (compliance).

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.