Intracranial Pressure Waveform Research Articles

An active learning framework for enhancing identification of non-artifactual intracranial pressure waveforms

Objective: Intracranial pressure (ICP) is an important and established clinical measurement that is used in the management of severe acute brain injury. ICP waveforms are usually triphasic and are susceptible to artifact because of transient catheter malfunction or routine patient care. Existing methods for artifact detection include threshold-based, stability-based, or template matching, and result in higher false positives (when there is variability in the ICP waveforms) or higher false negatives (when the ICP waveforms lack complete triphasic components but are valid). Approach: We hypothesized that artifact labeling of ICP waveforms can be optimized by an active learning approach which includes interactive querying of domain experts to identify a manageable number of informative training examples. Main results: The resulting active learning based framework identified non-artifactual ICP pulses with a superior AUC of 0.96 + 0.012, compared to existing methods: template matching (AUC: 0.71 + 0.04), ICP stability (AUC: 0.51 + 0.036) and threshold-based (AUC: 0.5 + 0.02). Significance: The proposed active learning framework will support real-time ICP-derived analytics by improving precision of artifact-labelling.

Cerebral Vascular Changes During Acute Intracranial Pressure Drop.

This study applied a new external ventricular catheter, which allows intracranial pressure (ICP) monitoring and cerebral spinal fluid (CSF) drainage simultaneously, to study cerebral vascular responses during acute CSF drainage. Six patients with 34 external ventricular drain (EVD) opening sessions were retrospectively analyzed. A published algorithm was used to extract morphological features of ICP recordings, and a template-matching algorithm was applied to calculate the likelihood of cerebral vasodilation index (VDI) and cerebral vasoconstriction index (VCI) based on the changes of ICP waveforms during CSF drainage. Power change (∆P) of ICP B-waves after EVD opening was also calculated. Cerebral autoregulation (CA) was assessed through phase difference between arterial blood pressure (ABP) and ICP using a previously published wavelet-based algorithm. The result showed that acute CSF drainage reduced mean ICP (P = 0.016) increased VCI (P = 0.02) and reduced ICP B-wave power (P = 0.016) significantly. VCI reacted to ICP changes negatively when ICP was between 10 and 25mmHg, and VCI remained unchanged when ICP was outside the 10-25mmHg range. VCI negatively (r = - 0.44) and VDI positively (r = 0.82) correlated with ∆P of ICP B-waves, indicating that stronger vasoconstriction resulted in bigger power drop in ICP B-waves. Better CA prior to EVD opening triggered bigger drop in the power of ICP B-waves (r = - 0.612). This study demonstrates that acute CSF drainage reduces mean ICP, and results in vasoconstriction which can be detected through an index, VCI. Cerebral vessels actively respond to ICP changes or cerebral perfusion pressure (CPP) changes in a certain range; beyond which, the vessels are insensitive to the changes in ICP and CPP.

Systemic cardiovascular inputs in models estimating intracranial pressure magnitude and waveform

BackgroundMonitoring Intracranial Pressure (ICP) is key for appropriate clinical treatment of patients with conditions potentially causing raised ICP. The adequacy of using Heart Rate (HR), aortic Blood Pressure (aBP) and carotid Blood Flow (cBF) to estimate ICP magnitude (pulse and mean) and waveform is investigated as an alternative means to invasive ICP measurement.MethodsICP (sequentially raised from resting ICP to 30–40 mmHg with infusions of artificial intracranial fluid), aBP (lowered with sodium nitroprus-side and raised with phenylephrine, 30 µg/kg/min, across a physiological range), HR (paced at 400 and 500 bpm), and cBF were measured in 11 anaesthetised Sprague Dawley rats. Potential cardiovascular predictors of ICP magnitude were assessed by stepwise mixed-model regression. Two transfer function models were constructed to estimate the ICP waveform from aBP or cBF waveforms.ResultsSystolic, mean and diastolic aBP as well as peak and minimum cBF had significant predictive value for mean ICP (p< 0.001, R2 = 0.25). HR (p< 0.05), systolic and mean aBP (p < 0.001), peak (p < 0.001), mean (p < 0.05) and minimum (p < 0.01) cBF had significant value for pulse ICP (R2 = 0.35). The transfer function models showed potential to reproduce the ICP waveform (Root Mean Square Error (RMSE) ≤4 mmHg), being more accurate for mean aBP above 100 mmHg and mean ICP below 20 mmHg (RMSE ≤ 0.5 mmHg).ConclusionsThe models developed from the comprehensive rat experiment demonstrated that systemic cardiovascular measures have predictive value in estimating the ICP magnitude and waveform, but other inputs may be necessary to improve accuracy in estimating ICP across the full physiological range.

A Precision Medicine Approach to Cerebral Edema and Intracranial Hypertension after Severe Traumatic Brain Injury: Quo Vadis?

Standard clinical protocols for treating cerebral edema and intracranial hypertension after severe TBI have remained remarkably similar over decades. Cerebral edema and intracranial hypertension are treated interchangeably when in fact intracranial pressure (ICP) is a proxy for cerebral edema but also other processes such as extent of mass lesions, hydrocephalus, or cerebral blood volume. A complex interplay of multiple molecular mechanisms results in cerebral edema after severe TBI, and these are not measured or targeted by current clinically available tools. Addressing these underpinnings may be key to preventing or treating cerebral edema and improving outcome after severe TBI. This review begins by outlining basic principles underlying the relationship between edema and ICP including the Monro-Kellie doctrine and concepts of intracranial compliance/elastance. There is a subsequent brief discussion of current guidelines for ICP monitoring/management. We then focus most of the review on an evolving precision medicine approach towards cerebral edema and intracranial hypertension after TBI. Personalization of invasive neuromonitoring parameters including ICP waveform analysis, pulse amplitude, pressure reactivity, and longitudinal trajectories are presented. This is followed by a discussion of cerebral edema subtypes (continuum of ionic/cytotoxic/vasogenic edema and progressive secondary hemorrhage). Mechanisms of potential molecular contributors to cerebral edema after TBI are reviewed. For each target, we present findings from preclinical models, and evaluate their clinical utility as biomarkers and therapeutic targets for cerebral edema reduction. This selection represents promising candidates with evidence from different research groups, overlap/inter-relatedness with other pathways, and clinical/translational potential. We outline an evolving precision medicine and translational approach towards cerebral edema and intracranial hypertension after severe TBI.

Utility of the Tympanic Membrane Pressure Waveform for Non-invasive Estimation of The Intracranial Pressure Waveform

Time domain analysis of the intracranial pressure (ICP) waveform provides important information about the intracranial pressure-volume reserve capacity. The aim here was to explore whether the tympanic membrane pressure (TMP) waveform can be used to non-invasively estimate the ICP waveform. Simultaneous invasive ICP and non-invasive TMP signals were measured in a total of 28 individuals who underwent invasive ICP measurements as a part of their clinical work up (surveillance after subarachnoid hemorrhage in 9 individuals and diagnostic for CSF circulation disorders in 19 individuals). For each individual, a transfer function estimate between the invasive ICP and non-invasive TMP signals was established in order to explore the potential of the method. To validate the results, ICP waveform parameters including the mean wave amplitude (MWA) were computed in the time domain for both the ICP estimates and the invasively measured ICP. The patient-specific non-invasive ICP signals predicted MWA rather satisfactorily in 4/28 individuals (14%). In these four patients the differences between original and estimated MWA were <1.0 mmHg in more than 50% of observations, and <0.5 mmHg in more than 20% of observations. The study further disclosed that the cochlear aqueduct worked as a physical lowpass filter.

Transfer Function Between Intracranial Pressure and Aortic Blood Pressure and Carotid Blood Flow.

The compliance of the intracranial space is such that the intracranial pressure (ICP) waveform is approximately the aortic blood pressure (BP) waveform minus the dominant harmonic (heart rate (HR)) of that waveform. This has been tested across species of different resting HR. Whether this filter characteristic holds true for large changes in HR, or under changed ICP, has not been examined. This study tested these changes in 11 anesthetized rats instrumented to measure and change ICP, HR, aortic BP, and carotid blood flow. The aortic BP to ICP and carotid blood flow to ICP transfer function was determined for normal ICP at paced HRs of 300, 400 and 500 bpm, and at raised ICP at HRs of 400 and 500 bpm. The aortic BP to ICP transfer function magnitude showed a dependency on HR HR (-0.15±0.04 ×10-3 bpm-1, p<0.001) and mean ICP (4.4±0.6 ×10-3 mmHg-1). The carotid blood flow to ICP transfer function magnitude showed a dependency on mean ICP (11.1±1.8 ×10-3 mmHg/ml/min/mmHg, p<0.001) but not on HR. The changes with different HRs indicates a degree of non-linearity in the system. Though small, this may need to be accounted for in understanding the relationship between systemic BP and flow and ICP. This data is useful in understanding the relationship between cardiovascular signals and ICP, valuable in advancing the ability to estimate ICP non-invasively.

Venous waveform morphological changes associated with treatment of symptomatic venous sinus stenosis

IntroductionVenous outflow obstruction is recognized as a contributing factor in a subset of patients with idiopathic intracranial hypertension (IIH). Little is known about venous sinus waveform morphology or how it...

Non-invasive Estimation of the Intracranial Pressure Waveform from the Central Arterial Blood Pressure Waveform in Idiopathic Normal Pressure Hydrocephalus Patients

This study explored the hypothesis that the central aortic blood pressure (BP) waveform may be used for non-invasive estimation of the intracranial pressure (ICP) waveform. Simultaneous invasive ICP and radial artery BP waveforms were measured in 29 individuals with idiopathic normal pressure hydrocephalus (iNPH). The central aortic BP waveforms were estimated from the radial artery BP waveforms using the SphygmoCor system. For each individual, a transfer function estimate between the central aortic BP and the invasive ICP waveforms was found (Intra-patient approach). Thereafter, the transfer function estimate that gave the best fit was chosen and applied to the other individuals (Inter-patient approach). To validate the results, ICP waveform parameters were calculated for the estimates and the measured golden standard. For the Intra-patient approach, the mean absolute difference in invasive versus non-invasive mean ICP wave amplitude was 1.9 ± 1.0 mmHg among the 29 individuals. Correspondingly, the Inter-patient approach resulted in a mean absolute difference of 1.6 ± 1.0 mmHg for the 29 individuals. This method gave a fairly good estimate of the wave for about a third of the individuals, but the variability is quite large. This approach is therefore not a reliable method for use in clinical patient management.

Restoration of Blood Flow to the Proximal Femoral Epiphysis in Unstable Slipped Capital Femoral Epiphysis by Modified Dunn Procedure: A Preliminary Angiographic and Intracranial Pressure Monitoring Study.

The major complication of unstable slipped capital femoral epiphysis (SCFE) is avascular necrosis (AVN) of the femoral head. The purpose of this study was to document by angiography the preoperative and postoperative perfusion to the proximal femoral epiphysis following an unstable SCFE. A specific aim was to determine whether blood flow could be restored. A secondary aim was to determine the efficacy of an intracranial pressure (ICP) monitor to assess blood flow within the femoral head intraoperatively. Nine patients with an unstable SCFE underwent superselective angiogram of the medial circumflex femoral artery preoperatively, followed by operative fixation with an open reduction using a modified Dunn approach. Femoral head blood flow was evaluated with an ICP monitor. Angiography was repeated postoperatively. Patients were followed radiographically to assess for AVN. Follow-up averaged 22 months. Six patients did not have arterial flow to the femoral head on the preoperative angiogram. Flow was restored postoperatively on angiogram in 4 of the 6 patients. Two patients developed AVN. One had no flow to the femoral head preoperatively or postoperatively on angiogram and complete tearing of the periosteum was noted. In 1 patient, there was no ICP waveform after the initial reduction. After removing more callous and repeating reduction, the waveform returned. Of the 2 patients with AVN, 1 had an ICP waveform after reduction. This study documents that some patients with unstable SCFE present with reduced femoral head blood supply due to SCFE. It also demonstrates blood flow restoration in 4 patients by angiogram and 5 by ICP monitor after surgical treatment. No patient immediately lost blood flow due to surgery. ICP monitor is a safe intraoperative tool for real-time assessment of femoral head blood flow during open reduction of unstable SCFE. Presence of flow by ICP is not a guarantee that AVN will not develop, but absence of flow was predictive of AVN. Therapeutic level I-prognostic. See Instructions for Authors for a complete description of levels of evidence.

Multi-Scale Peak and Trough Detection Optimised for Periodic and Quasi-Periodic Neuroscience Data.

The reliable detection of peaks and troughs in physiological signals is essential to many investigative techniques in medicine and computational biology. Analysis of the intracranial pressure (ICP) waveform is a particular challenge due to multi-scale features, a changing morphology over time and signal-to-noise limitations. Here we present an efficient peak and trough detection algorithm that extends the scalogram approach of Scholkmann et al., and results in greatly improved algorithm runtime performance. Our improved algorithm (modified Scholkmann) was developed and analysed in MATLAB R2015b. Synthesised waveforms (periodic, quasi-periodic and chirp sinusoids) were degraded with white Gaussian noise to achieve signal-to-noise ratios down to 5 dB and were used to compare the performance of the original Scholkmann and modified Scholkmann algorithms. The modified Scholkmann algorithm has false-positive (0%) and false-negative (0%) detection rates identical to the original Scholkmann when applied to our test suite. Actual compute time for a 200-run Monte Carlo simulation over a multicomponent noisy test signal was 40.96 ± 0.020 s (mean ± 95%CI) for the original Scholkmann and 1.81 ± 0.003 s (mean ± 95%CI) for the modified Scholkmann, demonstrating the expected improvement in runtime complexity from [Formula: see text] to [Formula: see text]. The accurate interpretation of waveform data to identify peaks and troughs is crucial in signal parameterisation, feature extraction and waveform identification tasks. Modification of a standard scalogram technique has produced a robust algorithm with linear computational complexity that is particularly suited to the challenges presented by large, noisy physiological datasets. The algorithm is optimised through a single parameter and can identify sub-waveform features with minimal additional overhead, and is easily adapted to run in real time on commodity hardware.

Do ICP-Derived Parameters Differ in Vegetative State from Other Outcome Groups After Traumatic Brain Injury?

In nearly 1,000 traumatic brain injury (TBI) patients monitored in the years 1992-2014, we identified 18 vegetative state (VS) cases. Our database provided access to continuous computer-recorded signals, which we used to compare primary signals, intracranial pressure (ICP)-derived indices and demographic data between VS patients, patients who survived but who were not VS (S), and patients who died (D). Mean values of ICP, arterial blood pressure (ABP) and cerebral perfusion pressure (CPP) from the whole monitoring periods were compared between the different outcome groups. Secondary indices included pressure reactivity index (PRx), the magnitude of slow ICP vasogenic waves, the pulse amplitude of the first harmonic component of the ICP waveform and heart rate (HR). Mean blood pressure was lowest in the VS group-significantly in comparison to those who died (p = 0.02) and almost significantly (p = 0.1) in comparison to the patients who survived. Mean ICP in VS patients was lower than those who died (VS, 13 ± 5 mmHg; D, 22 ± 14 mmHg; p < 0.001), but not significantly different from those who survived (p > 0.05). The magnitude of slow vasogenic ICP waves was the same in VS patients and those who died, but significantly lower than in those who survived (S, 1.04 ± 0.57 mmHg; VS, 0.74 ± 0.45; p = 0.01). Patients who progress to a VS differ from non-VS survivors in displaying decreased power of slow vasogenic waves and from those who die by not experiencing as high a burden of intracranial hypertension.

Critical Thresholds of ICP Derived Continuous Cerebrovascular Reactivity Indices for outcome prediction in Non-Craniectomized TBI Patients: PRx, PAx and RAC.

To compare ICP derived cerebrovascular reactivity indices in their ability to predict 6-month outcome, and to determine/compare critical thresholds related to outcome for each index, in adult non-craniectomized traumatic brain injury (TBI). Using a retrospective cohort of non-decompressive craniectomy (non-DC) TBI patients, we performed univariate and multivariate binary logistic regression outcome analysis of: pressure reactivity index (PRx), pulse amplitude index (PAx) and a newly described index calculated as the Regression coefficient between intracranial pressure (ICP) waveform Amplitude and Cerebral perfusion pressure RAC (CPP). Finally, we performed sequential chi-square threshold analysis for each index as they related to 6-month binary outcomes. Outcome was assessed via dichotomized Glasgow Outcome Scores (GOS): A. Favourable (GOS 4 or 5) vs. Unfavourable (GOS 3 or less), B. Alive vs. Dead. 358 non-DC TBI patients were included in all aspects of the analysis. In an analysis of the entire recordin...

Critical Thresholds of Intracranial Pressure-Derived Continuous Cerebrovascular Reactivity Indices for Outcome Prediction in Noncraniectomized Patients with Traumatic Brain Injury.

The aim of the study was to compare intracranial pressure (ICP)-derived cerebrovascular reactivity indices in their ability to predict six-month outcome, and to determine/compare critical thresholds related to outcome for each index in adult noncraniectomized traumatic brain injury (TBI). Using a retrospective cohort of nondecompressive craniectomy (non-DC) patients with TBI, we performed univariate and multi-variate binary logistic regression outcome analysis of: pressure reactivity index (PRx), pulse amplitude index (PAx), and a newly described index (RAC) calculated as the regression coefficient between ICP waveform amplitude and cerebral perfusion pressure (CPP). Finally, we performed sequential chi-square threshold analysis for each index as it related to six-month binary outcomes. Outcome was assessed via dichotomized Glasgow Outcome Scores (GOS): (A) favorable (GOS 4 or 5) versus unfavorable (GOS 3 or less), (B) alive versus dead. There were 358 non-DC patients with TBI included in all aspects of the analysis. In an analysis of the entire recording period for all patients using univariate binary logistic regression, the areas under the curves (AUCs) for favorable versus unfavorable outcome were: PRx (0.573, p < 0.0001), PAx (0.606, p < 0.0001), and RAC (0.655, p < 0.0001). Similarly, the AUCs for alive versus dead outcome were: PRx (0.651, p < 0.0001), PAx (0.705, p < 0.0001), and RAC (0.722, p < 0.0001). RAC displayed superior AUC statistics compared with PRx and PAx, using both univariate and multi-variate regression. RAC displayed more stable critical thresholds related to six-month outcomes. Thresholds for both favorable versus unfavorable and alive versus dead outcomes for PRx, PAx, and RAC across the entire recording period were: +0.35 and +0.35, 0 and +0.25, -0.10 and -0.05, respectively. In non-DC patients with TBI, RAC appears to be superior to PRx and PAx in six-month outcome prediction, using both univariate and multi-variate logistic regression. Further, RAC displayed more stable critical thresholds associated with binary outcomes at six months. Further analysis of RAC in TBI is required.

A Detailed Protocol for Physiological Parameters Acquisition and Analysis in Neurosurgical Critical Patients.

Intracranial pressure (ICP) monitoring is now widely used in neurosurgical critical patients. Besides mean ICP value, the ICP derived parameters such as ICP waveform, amplitude of pulse (AMP), the correlation of ICP amplitude and ICP mean (RAP), pressure reactivity index (PRx), ICP and arterial blood pressure (ABP) wave amplitude correlation (IAAC), and so on, can reflect intracranial status, predict prognosis, and can also be used as guidance of proper treatment. However, most of the clinicians focus only on the mean ICP value while ignoring these parameters because of the limitations of the current devices. We have recently developed a multimodality monitoring system to address these drawbacks. This portable, user-friendly system will use a data collecting and storing device to continuously acquire patients' physiological parameters first, i.e., ABP, ICP, and oxygen saturation, and then analyze these physiological parameters. We hope that the multimodality monitoring system will be accepted as a key measure to monitor physiological parameters, to analyze the current clinical status, and to predict the prognosis of the neurosurgical critical patients.

Intracranial Pressure Values Are Highly Variable After Cerebral Spinal Fluid Drainage.

Intracranial pressure (ICP) is often obtained via external ventricular drain (EVD) placement and is discussed as a key vital sign in neuroscience. Nurses are most often delegated the task of observing, adjudicating, and documenting ICP. Cerebrospinal fluid drainage requires that the transducer connected to the EVD is open to drain, prohibiting ICP monitoring. There are no recent data to support an evidence-based standard for the period an ICP waveform should be observed, after the EVD is clamped, to be able to adjudicate a value that represents the patient's status. Therefore, the purpose of this study is to determine the optimal period for which an EVD should be closed to obtain an accurate ICP value. In a sample of 30 subjects who received continuous ICP monitoring for 15 minutes, there was no universal pattern to ICP after clamping an EVD. The conditional probability of observing a patient's highest ICP, if ICP is observed for 5 minutes, is 0.0181. The conditional probability increased to 0.0402 if ICP is observed for 10 minutes. There were no instances of ICP elevation requiring intervention. The results suggest that at least 5 minutes of ICP monitoring is safe and is required to provide an ICP value that reflects true ICP.

Novel method for dynamic control of intracranial pressure.

OBJECT Intracranial pressure (ICP) pulsations are generally considered a passive result of the pulsatility of blood flow. Active experimental modification of ICP pulsations would allow investigation of potential active effects on blood and CSF flow and potentially create a new platform for the treatment of acute and chronic low blood flow states as well as a method of CSF substance clearance and delivery. This study presents a novel method and device for altering the ICP waveform via cardiac-gated volume changes. METHODS The novel device used in this experiment (named Cadence) consists of a small air-filled inelastic balloon (approximately 1.0 ml) implanted into the intracranial space and connected to an external programmable pump, triggered by an R-wave detector. Balloons were implanted into the epidural space above 1 of the hemispheres of 19 canines for up to 10 hours. When activated, the balloons were programed to cyclically inflate with the cardiac cycle with variable delay, phase, and volume. The ICP response was measured in both hemispheres. Additionally, cerebral blood flow (heat diffusion and laser Doppler) was studied in 16 canines. RESULTS This system, depending on the inflation pattern of the balloon, allowed a flattening of the ICP waveform, increase in the ICP waveform amplitude, or phase shift of the wave. This occurred with small mean ICP changes, typically around ± 2 mm Hg (15%). Bilateral ICP effects were observed with activation of the device: balloon inflation at each systole increased the systolic ICP pulse (up to 16 mm Hg, 1200%) and deflation at systole decreased or even inverted the systolic ICP pulse (-0.5 to -19 mm Hg, -5% to -1600%) in a dose-(balloon volume) dependent fashion. No aphysiological or deleterious effects on systemic pressure (≤ ±10 mm Hg; 13% change in mean pressure) or cardiac rate (≤ ± 17 beats per minute; 16% change) were observed during up to 4 hours of balloon activity. CONCLUSIONS The results of these initial studies using an intracranially implanted, cardiac-gated, volume-oscillating balloon suggest the Cadence device can be used to modify ICP pulsations, without physiologically deleterious effects on mean ICP, systemic vascular effects, or brain injury. This device and technique may be used to study the role of ICP pulsatility in intracranial hemo- and hydrodynamic processes and introduces the creation of a potential platform of a cardiac-gated system for treatment of acute and chronic low blood flow states, and diseases requiring augmentation of CSF substance clearance or delivery.

B-waves revisited

Abstract Reduced intracranial compliance is a key manifestation common to a number of pathological conditions of the brain. It is encountered in, but not limited to, traumatic brain injury, cerebral edema, and hydrocephalus. There are no clinically accepted methods to measure intracranial compliance available to date. Intracranial pressure (ICP) waveform analysis is seeing a revival driven by advances in our understanding of cerebrospinal fluid and pressure dynamics. Its translation to widespread clinical use is dependent on the possibility to derive relevant metrics such as intracranial compliance reliably and non-invasively. The B-wave is one of the features of the ICP waveform, reflecting vasogenic activity of cerebral autoregulation. B-waves were originally defined to occupy the 0.5 to 2 cycles per minute frequency range. Recently renamed and redefined as slow waves with an extended range of 0.33 to 3 cycles per minute, specific changes in their pattern of occurrence are considered to be indicative of reduced intracranial compliance. With the still unmet need for a clinically acceptable method for acquiring intracranial compliance, and the revival of ICP waveform analysis, B-waves are moving back into the research focus. Herein we provide a concise review of the literature on B-waves, including a critical assessment of non-invasive methods for obtaining B-wave surrogates.

Intracranial Pressure Waveforms are More Closely Related to Central Aortic than Radial Pressure Waveforms: Implications for Pathophysiology and Therapy.

In patients with subarachnoid haemorrhage, pulsatile intracranial pressure (ICP) is more strongly associated with adverse events than mean ICP. Furthermore, patients with idiopathic normal-pressure hydrocephalus (iNPH), and pulsatile ICP of 5 mmHg or more, gain more benefit from cerebrospinal fluid (CSF) shunting than those whose pulsatile ICP is lower than 5 mmHg.Our study aims to investigate the morphological relationship between ICP pulsations, aortic pressure pulsations and radial artery pulsations. Central aortic pulse pressure has been known to be the best predictor of adverse cardiac events, whereas radial artery pulse pressure is generally measured and displayed in intensive care environments.We studied 10 patients with iNPH, and their ICP and aortic and radial pressures were digitised, ensemble-averaged and compared in the time and frequency domains. The ICP wave contour was quite different to the radial pressure waveform. By contrast, the ICP waveform was similar to the aortic pressure wave contour. The ICP amplitude averaged <10 % of aortic pulse pressure. In the frequency domain, the relative amplitude of the first three harmonics was similar for the ICP and aortic pressure. Hence, monitoring central aortic pressure through derivation from the radial pressure wave is superior to measurement of radial pressure alone.

Reproduction of ICP Waveform Changes in a Mathematical Model of the Cerebrospinal Circulatory System.

This study describes the establishment of a model of cerebral blood flow dynamics using cerebral blood flow velocity and intracranial pressure waveforms.

Change in Pulsatile Cerebral Arterial Pressure and Flow Waves as a Therapeutic Strategy?

While intracranial pressure (ICP), arterial pressure and transcranial middle cerebral artery flow velocity (MCAFV) are often monitored in unconscious patients following stroke or head injury, the value of waveform indices has not been fully established. We retrospectively analysed the data of eight adults (aged 19-36 years) with closed head injury who had spontaneous and repeated episodes of elevated ICP (i.e. "plateau waves"). MCAFV was measured using transcranial Doppler, ICP using a Codman catheter and radial artery pressure using cannulation. Ascending aortic pressure (AAP) was generated from the radial artery using SphygmoCor(TM). Cerebral perfusion pressure (CPP) was calculated as AAP - ICP in the time domain.During the period of increased ICP, ICP and cerebral flow velocity amplitude increased significantly compared with the basal condition, while cerebral mean flow decreased. Amplitude of the secondary peak in ICP, AAP and MCAFV waveform became apparent.An increase in the amplitude of ICP, AAP and MCAFV waves can be attributed to the greater prominence of reflected waves from the lower body, which was apparent in pulse waveform analysis. Arterial vasodilators such as nitrates reduce reflected pressure waves from the lower body and, by decreasing the amplitude of AAP, ICP and MCAFV, may be as beneficial for the cerebral circulation as they are for the left ventricle of the heart.