Origin of cerebrospinal fluid pulsations

Characterization of pulsations in the brain and cerebrospinal fluid using ultra-high field magnetic resonance imaging

The development of innovative non-invasive neuroimaging methods and biomarkers is critical for studying brain disease. Imaging of cerebrospinal fluid (CSF) pulsatility may inform the brain fluid dynamics involved in clearance of cerebral metabolic waste. In this work, we developed a methodology to characterize the frequency and spatial localization of whole brain CSF pulsations in humans. Using 7 Tesla (T) human magnetic resonance imaging (MRI) and ultrafast echo-planar imaging (EPI), in-vivo images were obtained to capture pulsations of the CSF signal. Physiological data were simultaneously collected and compared with the 7 T MR data. The primary components of signal pulsations were identified using spectral analysis, with the most evident frequency bands identified around 0.3, 1.2, and 2.4 Hz. These pulsations were mapped spatially and temporally onto the MR image domain and temporally onto the physiological measures of electrocardiogram and respiration. We identified peaks in CSF pulsations that were distinct from peaks in grey matter and white matter regions. This methodology may provide novel in vivo biomarkers of disrupted brain fluid dynamics.

Characterization of oscillations in the brain and cerebrospinal fluid using ultra-high field magnetic resonance imaging

Development of innovative non-invasive neuroimaging methods and biomarkers are critical for studying brain disease. In this work, we have developed a methodology to characterize the frequency responses and spatial localization of oscillations and movements of cerebrospinal fluid (CSF) flow in the human brain. Using 7 Tesla human MRI and ultrafast echo-planar imaging (EPI), in-vivo images were obtained to capture CSF oscillations and movements. Physiological data was simultaneously collected and correlated with the 7T MR data. The primary components of CSF oscillations were identified using spectral analysis (with frequency bands identified around 0.3Hz, 1.2Hz and 2.4Hz) and were mapped spatially and temporally onto the MR image domain and temporally onto the physiological domain. The developed methodology shows a good consistency and repeatability (standard deviation of 0.052 and 0.078 for 0.3Hz and 1.2Hz bands respectively) in-vivo for potential brain dynamics and CSF flow and clearance studies.

Cerebral arterial flow dynamics during systole and diastole phases in young and older healthy adults

BACKGROUND

Since arterial flow is the leading actor in neuro-fluids flow dynamics, it might be interesting to assess whether it is meaningful to study the arterial flow waveform in more detail and whether this provides new important information. Few studies have focused on determining the influence of heart rate variation over time on the arterial flow curve. Therefore, this study aimed to evaluate cerebral arterial flow waveforms at extracranial and intracranial compartments in young and elderly healthy adults, also considering systole and diastole phases.

METHODS

Cine phase-contrast magnetic resonance imaging (CINE-PC MRI) was performed on twenty-eight healthy young volunteers (HYV) and twenty healthy elderly volunteers (HEV) to measure arterial blood flows at the extracranial and intracranial planes. A semi-automated protocol using MATLAB scripts was implemented to identify the main representative points in the arterial flow waveforms. Representative arterial profiles were estimated for each group. Moreover, the effects of age and sex on flow times, amplitude-related parameters, and parameters related to systole and diastole phases were evaluated at the extracranial and intracranial compartments. Student's t-test or Wilcoxon's test (depending on the normality of the distribution) was used to detect significant differences.

RESULTS

In HYVs, significant differences were observed between extracranial and intracranial levels in parameters related to the AP1 amplitude. Besides the detected differences in pulsatility index (extracranial: 0.92 ± 0.20 vs. 1.28 ± 0.33; intracranial: 0.79 ± 0.15 vs. 1.14 ± 0.18, p < .001) and average flow (715 ± 136 vs. 607 ± 125 ml/min, p = .008) between HYV and HEV, differences in the amplitude value of the arterial flow profile feature points were also noted. Contrary to systole duration (HYV: 360 ± 29 ms; HEV: 364 ± 47 ms), diastole duration presented higher inter-individual variability in both populations (HYV: 472 ± 145 ms; HEV: 456 ± 106 ms). Our results also showed that, with age, it is mainly the diastolic phase that changes. Although no significant differences in duration were observed between the two populations, the mean flow value in the diastolic phase was significantly lower in HEV (extracranial: 628 ± 128 vs. 457 ± 111 ml/min; intracranial: 599 ± 121 vs. 473 ± 100 ml/min, p < .001). No significant differences were observed in the arterial flow parameters evaluated between females and males in either HYV or HEV.

CONCLUSION

Our study provides a novel contribution on the influence of the cardiac cycle phases on cerebral arterial flow. The main contribution in this study concerns the identification of age-related alterations in cerebral blood flow, which occur mainly during the diastolic phase. Specifically, we observed that mean flow significantly decreases with age during diastole, whereas mean flow during systole is consistent.

Characterising spinal cerebrospinal fluid flow in the pig with phase-contrast magnetic resonance imaging

BACKGROUND

Detecting changes in pulsatile cerebrospinal fluid (CSF) flow may assist clinical management decisions, but spinal CSF flow is relatively understudied. Traumatic spinal cord injuries (SCI) often cause spinal cord swelling and subarachnoid space (SAS) obstruction, potentially causing pulsatile CSF flow changes. Pigs are emerging as a favoured large animal SCI model; therefore, the aim of this study was to characterise CSF flow along the healthy pig spine.

METHODS

Phase-contrast magnetic resonance images (PC-MRI), retrospectively cardiac gated, were acquired for fourteen laterally recumbent, anaesthetised and ventilated, female domestic pigs (22-29 kg). Axial images were obtained at C2/C3, T8/T9, T11/T12 and L1/L2. Dorsal and ventral SAS regions of interest (ROI) were manually segmented. CSF flow and velocity were determined throughout a cardiac cycle. Linear mixed-effects models, with post-hoc comparisons, were used to identify differences in peak systolic/diastolic flow, and maximum velocity (cranial/caudal), across spinal levels and dorsal/ventral SAS. Velocity wave speed from C2/C3 to L1/L2 was calculated.

RESULTS

PC-MRI data were obtained for 11/14 animals. Pulsatile CSF flow was observed at all spinal levels. Peak systolic flow was greater at C2/C3 (dorsal: - 0.32 ± 0.14 mL/s, ventral: - 0.15 ± 0.13 mL/s) than T8/T9 dorsally (- 0.04 ± 0.03 mL/s; p < 0.001), but not different ventrally (- 0.08 ± 0.08 mL/s; p = 0.275), and no difference between thoracolumbar levels (p > 0.05). Peak diastolic flow was greater at C2/C3 (0.29 ± 0.08 mL/s) compared to T8/T9 (0.03 ± 0.03 mL/s, p < 0.001) dorsally, but not different ventrally (p = 1.000). Cranial and caudal maximum velocity at C2/C3 were greater than thoracolumbar levels dorsally (p < 0.001), and T8/T9 and L1/L2 ventrally (p = 0.022). Diastolic velocity wave speed was 1.41 ± 0.39 m/s dorsally and 1.22 ± 0.21 m/s ventrally, and systolic velocity wave speed was 1.02 ± 0.25 m/s dorsally and 0.91 ± 0.22 m/s ventrally.

CONCLUSIONS

In anaesthetised and ventilated domestic pigs, spinal CSF has lower pulsatile flow and slower velocity wave propagation, compared to humans. This study provides baseline CSF flow at spinal levels relevant for future SCI research in this animal model.

Intracranial pulse pressure waveform analysis using the higher harmonics centroid

Background

The pulse waveform of intracranial pressure (ICP) is its distinctive feature almost always present in the clinical recordings. In most cases, it changes proportionally to rising ICP, and observation of these changes may be clinically useful. We introduce the higher harmonics centroid (HHC) which can be defined as the center of mass of harmonics of the ICP pulse waveform from the 2nd to 10th, where mass corresponds to amplitudes of these harmonics. We investigate the changes in HHC during ICP monitoring, including isolated episodes of ICP plateau waves.

Material and methods

Recordings from 325 patients treated between 2002 and 2010 were reviewed. Twenty-six patients with ICP plateau waves were identified. In the first step, the correlation between HHC and ICP was examined for the entire monitoring period. In the second step, the above relation was calculated separately for periods of elevated ICP during plateau wave and the baseline.

Results

For the values averaged over the whole monitoring period, ICP (22.3 ± 6.9 mm Hg) correlates significantly (R = 0.45, p = 0.022) with HHC (3.64 ± 0.46). During the ICP plateau waves (ICP increased from 20.9 ± 6.0 to 53.7 ± 9.7 mm Hg, p < 10⁻¹⁶), we found a significant decrease in HHC (from 3.65 ± 0.48 to 3.21 ± 0.33, p = 10⁻⁵).

Conclusions

The good correlation between HHC and ICP supports the clinical application of pressure waveform analysis in addition to the recording of ICP number only. Mean ICP may be distorted by a zero drift, but HHC remains immune to this error. Further research is required to test whether a decline in HHC with elevated ICP can be an early warning sign of intracranial hypertension, whether individual breakpoints of correlation between ICP and its centroid are of clinical importance.

Intraoperative monitoring of CSF pressure in patients with degenerative cervical myelopathy (COMP-CORD Study): a prospective cohort study

Degenerative cervical myelopathy (DCM) is hallmarked by spinal canal narrowing and related cord compression and myelopathy. CSF pressure dynamics are likely disturbed due to spinal canal stenosis. The study aims to investigate the diagnostic value of continuous intraoperative CSF pressure monitoring during surgical decompression. Prospective single center study (NCT02170155) with enrolment of DCM patients that underwent surgical decompression between December 2019 and May 2021. Data from N=17 patients were analyzed, symptom severity graded with the modified Japanese Orthopedic Score (mJOA). CSF pulsations were continuously monitored with a lumbar intrathecal catheter during surgical decompression. Mean patient age was 62±9 years (range 38-73; 8F), symptoms were mild-moderate in most patients (mean mJOA 14±2, range 10-18). Measurements were well tolerated without safety concerns. In 15/16 (94%) CSF pulsations increased at the time of surgical decompression. In one case, responsiveness could not be evaluated for technical reasons. Unexpected CSF pulsation decrease was related to adverse events (i.e., CSF leakage). Median CSF pulsation amplitudes increased from pre-decompression (0.52 mmHg [IQR 0.71]) to post-decompression (0.72 mmHg [IQR 0.96]) (P=0.001). Mean baseline CSF pressure increased with lower magnitude than pulsations, from 9.5±3.5 to 10.3±3.8 mmHg (P=0.003). Systematic relations of CSF pulsations were confined to surgical decompression, independent of arterial blood pressure (P=0.927) or heart rate (P=0.102). Intraoperative CSF pulsation monitoring was sensitive, timely, and specifically related to surgical decompression while in addition adverse events could be discerned. Further investigation of the clinical value of intraoperative guidance for decompression in complex DCM surgery is promising.

Intracranial Pressure Monitoring Signals After Traumatic Brain Injury: A Narrative Overview and Conceptual Data Science Framework

Continuous intracranial pressure (ICP) monitoring is a cornerstone of neurocritical care after severe brain injuries such as traumatic brain injury and acts as a biomarker of secondary brain injury. With the rapid development of artificial intelligent (AI) approaches to data analysis, the acquisition, storage, real-time analysis, and interpretation of physiological signal data can bring insights to the field of neurocritical care bioinformatics. We review the existing literature on the quantification and analysis of the ICP waveform and present an integrated framework to incorporate signal processing tools, advanced statistical methods, and machine learning techniques in order to comprehensively understand the ICP signal and its clinical importance. Our goals were to identify the strengths and pitfalls of existing methods for data cleaning, information extraction, and application. In particular, we describe the use of ICP signal analytics to detect intracranial hypertension and to predict both short-term intracranial hypertension and long-term clinical outcome. We provide a well-organized roadmap for future researchers based on existing literature and a computational approach to clinically-relevant biomedical signal data.

A Spectral Approach to Model-Based Noninvasive Intracranial Pressure Estimation

BACKGROUND

Intracranial pressure (ICP) normally ranges from 5 to 15 mmHg. Elevation in ICP is an important clinical indicator of neurological injury, and ICP is therefore monitored routinely in several neurological conditions to guide diagnosis and treatment decisions. Current measurement modalities for ICP monitoring are highly invasive, largely limiting the measurement to critically ill patients. An accurate noninvasive method to estimate ICP would dramatically expand the pool of patients that could benefit from this cranial vital sign.

METHODS

This article presents a spectral approach to model-based ICP estimation from arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) measurements. The model captures the relationship between the ABP, CBFV, and ICP waveforms and utilizes a second-order model of the cerebral vasculature to estimate ICP.

RESULTS

The estimation approach was validated on two separate clinical datasets, one recorded from thirteen pediatric patients with a total duration of around seven hours, and the other recorded from five adult patients, one hour and 48 minutes in total duration. The algorithm was shown to have an accuracy (mean error) of 0.4 mmHg and -1.5 mmHg, and a precision (standard deviation of the error) of 5.1 mmHg and 4.3 mmHg, in estimating mean ICP (range of 1.3 mmHg to 24.8 mmHg) on the pediatric and adult data, respectively. These results are comparable to previous results and within the clinically relevant range. Additionally, the accuracy and precision in estimating the pulse pressure of ICP on a beat-by-beat basis were found to be 1.3 mmHg and 2.9 mmHg respectively.

CONCLUSION

These contributions take a step towards realizing the goal of implementing a real-time noninvasive ICP estimation modality in a clinical setting, to enable accurate clinical-decision making while overcoming the drawbacks of the invasive ICP modalities.

Evaluation of basilar artery and cerebrospinal fluid dynamics using phase-contrast MRI: Comparison between mannitol and isotonic saline solution

Increased intracranial pressure (ICP) can cause irreversible pathological changes in the canine brain and can be life-threatening, so prompt diagnosis and therapeutic responses are warranted. The purposes of this prospective experimental study were to evaluate phase-contrast MRI (PC-MRI) as a non-invasive method for quantifying cerebrospinal fluid (CSF) and basilar artery flow, and to assess effects of intravenous administration of hypertonic fluid. A PC-MRI scan was acquired for six healthy Beagle dogs at the level of the mesencephalic aqueduct. Either 1.0 g/kg mannitol or isotonic saline solution was administered intravenously for 15 min each at a matched dose volume of 5 mL/kg. Basilar artery and CSF flow rates were measured and their values compared between mannitol and isotonic saline solution groups before administration, and subsequently every 15 min for 2 h post-administration. The CSF dynamics were further assessed by measuring repeat flow from the caudal to rostral direction and the rostral to caudal direction as the number of waves. No significant difference was observed in basilar or and CSF flow velocity between the two groups (P > .05). However, administration of isotonic saline solution tended to increase basilar artery velocity slightly over time, while CSF velocity remained unchanged. In the mannitol group, CSF wave forms tended to be reduced at 60 and 75 min (P > .05). Findings from this preliminary study indicated that it is feasible to measure the dynamics of CSF and basilar artery flow by PC-MRI, but no flow differences could be detected for mannitol versus isotonic saline administration.

Morphological changes of intracranial pressure quantifies vasodilatory effect of verapamil to treat cerebral vasospasm

INTRODUCTION

After aneurysmal subarachnoid hemorrhage (SAH), both proximal and distal cerebral vasospasm can contribute to the development of delayed cerebral ischemia. Intra-arterial (IA) vasodilators are a mainstay of treatment for distal arterial vasospasm, but no methods of assessing the efficacy of interventions in real time have been established.

OBJECTIVE

To introduce a new method for continuous intraprocedural assessment of endovascular treatment for cerebral vasospasm.

METHODS

The premise of our approach was that distal cerebral arterial changes induce a consistent pattern in the morphological changes of intracranial pressure (ICP) pulse. This premise was demonstrated using a published algorithm in previous papers. In this study, we applied the algorithm to calculate the likelihood of cerebral vasodilation (VDI) and cerebral vasoconstriction (VCI) from intraprocedural ICP signals that are synchronized with injection of the IA vasodilator, verapamil. Cerebral blood flow velocities (CBFVs) on bilateral cerebral arteries were studied before and after IA therapy.

RESULTS

192 recordings of patients with SAH were reviewed, and 27 recordings had high-quality ICP waveforms. The VCI was significantly lower after the first verapamil injection (0.47±0.017) than VCI at baseline (0.49±0.020, p<0.001). A larger dose of injected verapamil resulted in a larger and longer VDI increase. CBFV of the middle cerebral artery increases across the days before the injection of verapamil and decreases after IA therapy.

CONCLUSION

This study provides preliminary validation of an algorithm for continuous assessment of distal cerebral arterial changes in response to IA vasodilator infusion in patients with vasospasm and aneurysmal SAH.

Characteristics of the cerebrospinal fluid pressure waveform and craniospinal compliance in idiopathic intracranial hypertension subjects

BACKGROUND

Idiopathic intracranial hypertension (IIH) is a condition of abnormally high intracranial pressure with an unknown etiology. The objective of this study is to characterize craniospinal compliance and measure the cerebrospinal fluid (CSF) pressure waveform as CSF is passively drained during a diagnostic and therapeutic lumbar puncture (LP) in IIH.

METHODS

Eighteen subjects who met the Modified Dandy Criteria, including papilledema and visual field loss, received an ultrasound guided LP where CSF pressure (CSFP) was recorded at each increment of CSF removal. Joinpoint regression models were used to calculate compliance from CSF pressure and the corresponding volume removed at each increment for each subject. Twelve subjects had their CSFP waveform recorded with an electronic transducer. Body mass index, mean CSFP, and cerebral perfusion pressure (CPP) were also calculated. T-tests were used to compare measurements, and correlations were performed between parameters.

RESULTS

Cerebrospinal fluid pressure, CSFP pulse amplitude (CPA), and CPP were found to be significantly different (p < 0.05) before and after the LP. CSFP and CPA decreased after the LP, while CPP increased. The craniospinal compliance significantly increased (p < 0.05) post-LP. CPA and CSFP were significantly positively correlated.

CONCLUSIONS

Both low craniospinal compliance (at high CSFP) and high craniospinal compliance (at low CSFP) regions were determined. The CSFP waveform morphology in IIH was characterized and CPA was found to be positively correlated to the magnitude of CSFP. Future studies will investigate how craniospinal compliance may correlate to symptoms and/or response to therapy in IIH subjects.

ICP curve morphology and intracranial flow-volume changes: a simultaneous ICP and cine phase contrast MRI study in humans

Background

The intracranial pressure (ICP) curve with its different peaks has been extensively studied, but the exact physiological mechanisms behind its morphology are still not fully understood. Both intracranial volume change (ΔICV) and transmission of the arterial blood pressure have been proposed to shape the ICP curve. This study tested the hypothesis that the ICP curve correlates to intracranial volume changes.

Methods

Cine phase contrast magnetic resonance imaging (MRI) examinations were performed in neuro-intensive care patients with simultaneous ICP monitoring. The MRI was set to examine cerebral arterial inflow and venous cerebral outflow as well as flow of cerebrospinal fluid over the foramen magnum. The difference in total flow into and out from the cranial cavity (Flow_tot) over time provides the ΔICV. The ICP curve was compared to the Flow_tot and the ΔICV. Correlations were calculated through linear and logarithmic regression. Student’s t test was used to test the null hypothesis between paired samples.

Results

Excluding the initial ICP wave, P1, the mean R² for the correlation between the ΔICV and the ICP was 0.75 for the exponential expression, which had a higher correlation than the linear (p = 0.005). The first ICP peaks correlated to the initial peaks of Flow_tot with a mean R² = 0.88.

Conclusion

The first part, or the P1, of the ICP curve seems to be created by the first rapid net inflow seen in Flow_tot while the rest of the ICP curve seem to correlate to the ΔICV.

Energy harvesting from cerebrospinal fluid pressure fluctuations for self-powered neural implants

In this paper, a novel method to generate electrical energy by converting available mechanical energy from pressure fluctuations of the cerebrospinal fluid within lateral ventricles of the brain is presented. The generated electrical power can be supplied to the neural implants and either eliminate their battery need or extend the battery lifespan. A diaphragm type harvester comprised of piezoelectric material is utilized to convert the pressure fluctuations to electrical energy. The pressure fluctuations cause the diaphragm to bend, and the strained piezoelectric materials generate electricity. In the framework of this study, an energy harvesting structure having a diameter of 2.5 mm was designed and fabricated using microfabrication techniques. A 1:1 model of lateral ventricles was 3D-printed from raw MRI images to characterize the harvester. Experimental results show that a maximum power of 0.62 nW can be generated from the harvester under similar physical conditions in lateral ventricles which corresponds to energy density of 12.6 nW/cm². Considering the available area within the lateral ventricles and the size of harvesters that can be built using microfabrication techniques it is possible to amplify to power up to 26 nW. As such, the idea of generating electrical energy by making use of pressure fluctuations within brain is demonstrated in this work via the 3D-printed model system.

Morphological Feature Extraction From a Continuous Intracranial Pressure Pulse via a Peak Clustering Algorithm

OBJECTIVE

An increase in intracranial pressure (ICP) is frequently observed in patients with severe traumatic brain injury (TBI). The information derived from the observation of temporal changes in the mean ICP is insufficient for assessment of the compensatory reserve of the injured brain. This assessment can be achieved via continuous morphological analysis of the pulse waveform of the ICP.

METHODS

Continuous arterial blood pressure (ABP) and ICP recordings from 292 TBI patients were analyzed. The algorithm extracted morphological landmarks (peaks, troughs, and flats) from the ICP. Among the extracted peaks, P1, P2, and P3 were assigned through peak clustering. The performance of the proposed method was validated through a comparison of the algorithm-defined peaks and those manually identified by experienced observers.

RESULTS

The proposed algorithm successfully identified the three distinguishing peaks of the ICP with satisfactory accuracy (95.3%, 87.8%, and 87.5% for P1, P2, and P3, respectively), even from minimally filtered raw signals.

CONCLUSION

The algorithm extracted the morphological features from both ABP and ICP recordings with high accuracy.

SIGNIFICANCE

The ABP and ICP pulse waveforms can be simultaneously analyzed in real time using the proposed algorithm. The morphological features from these signals may aid the continuous care of patients with TBI.

Intracranial pressure pulse waveform correlates with aqueductal cerebrospinal fluid stroke volume

This study identifies a novel relationship between cerebrospinal fluid (CSF) stroke volume through the cerebral aqueduct and the characteristic peaks of the intracranial pulse (ICP) waveform. ICP waveform analysis has become much more advanced in recent years; however, clinical practice remains restricted to mean ICP, mainly due to the lack of physiological understanding of the ICP waveform. Therefore, the present study set out to shed some light on the physiological meaning of ICP morphological metrics derived by the morphological clustering and analysis of continuous intracranial pulse (MOCAIP) algorithm by investigating their relationships with a well defined physiological variable, i.e., the stroke volume of CSF through the cerebral aqueduct. Seven patients received both overnight ICP monitoring along with a phase-contrast MRI (PC-MRI) of the cerebral aqueduct to quantify aqueductal stroke volume (ASV). Waveform morphological analysis of the ICP signal was performed by the MOCAIP algorithm. Following extraction of morphological metrics from the ICP signal, nine temporal ICP metrics and two amplitude-based metrics were compared with the ASV via Spearman's rank correlation. Of the nine temporal metrics correlated with the ASV, only the width of the P2 region (ICP-Wi2) reached significance. Furthermore, both ICP pulse pressure amplitude and mean ICP did not reach significance. In this study, we showed the width of the second peak (ICP-Wi2) of an ICP pulse wave is positively related to the volume of CSF movement through the cerebral aqueduct. This finding is an initial step in bridging the gap between ICP waveform morphology research and clinical practice.

A new approach for investigating intracranial pressure signal: filtering and morphological features extraction from continuous recording

Nowadays, the Intracranial Pressure (ICP) monitoring has become the most common method of investigation for both traumatic and chronic neural pathologies. ICP signals are typically triphasic, that is, in a single waveform, three subpeaks can be identified. This work outlines a new algorithm to identify subpeaks from the ICP recordings and to extract a number of 20 meaningful parameter trends. The validity of the implemented method has been proved through a comparison between the automatic subpeaks identification by the algorithm and the manually marked subpeaks by a neurosurgeon. The automatic marking system has identified subpeaks for the 63.74% (mean value) of pulse waves, providing the position and amplitude of each identified subpeak within a tolerance of ±7 samples. This automatic system provides a feature set to be used by classification software to obtain more precise and easier diagnosis in all those cases that involve brain damages or diseases.

Lack of consistent intracranial pressure pulse morphological changes during episodes of microdialysis lactate/pyruvate ratio increase

Lactate/pyruvate ratio (LPR) from microdialysis is a well-established marker of cerebral metabolic crisis. For brain injury patients, abnormally high LPR could indicate cerebral ischemia or failure of O(2) uptake. However, there is a debate on the primary factor responsible for LPR increase. Exploiting the potential of using the morphology of a high temporal resolution signal such as intracranial pulse (ICP) to characterize cerebrovascular changes, a data analysis experiment is taken to test whether consistent changes in ICP pulse morphological metrics accompany the LPR increase. We studied 3517 h of LPR and continuous ICP data from 19 severe traumatic brain injury patients. Our morphological clustering and analysis of intracranial pressure (MOCAIP) algorithm was applied to ICP pulses, which were matched in time to the LPR measurements, and 128 pulse morphological metrics were extracted. We automatically identified the episodes of LPR increases using a moving time window of 10-20 h. We then studied the trending patterns of each of the 128 ICP MOCAIP metrics within these identified periods and determined them to be one of the following three types: increasing, decreasing or no trend. A binomial test was employed to investigate whether any MOCAIP metrics show a consistent trend among all episodes of LPR increase per patient. Regardless of the selected values for different parameters of the proposed method, for the majority of the subjects in the study (78%), none of the ICP metrics show any consistent trend during the episodes of LPR increase. Even for the few subjects who have at least one ICP metric with a consistent trend during the LPR increase episodes, the number of such metrics is small and varies from subject to subject. Given the fact that ICP pulse morphology is influenced by the cerebral vasculature, our results suggest that a dominant cerebral vascular cause may be behind the changes in LPR when LPR trends correlate with ICP pulse morphological changes. However, the incidence of such correlation seems to be low.

Role of chiropractic and sacro-occipital technique in asthma treatment

Asthma is a multifactorial dysfunction of the respiratory system. Nutritional, environmental, genetic, and emotional factors all play animportant part in the etiology of this condition. One form of chiropractic, Sacro Occipital Technique (SOT), offers some conservative alternatives to the treatment of asthma. SOT expands the chiropractic armamentarium of techniques available, allowing methods putatively affecting the viscera, vertebra, post and preganglionic reflexes, as well as cranial and sacral influences on the primary respiratory mechanism. Though more research is needed to evaluate the efficacy of chiropractic care of asthma, the conservative nature of chiropractic care with its minimal side effects, warrants patient and a health practitioner's consideration prior to embarking on any course of treatment that might have serious side effects.

Intracranial pressure pulse morphological features improved detection of decreased cerebral blood flow

We investigated whether intracranial pressure (ICP) pulse morphological metrics could be used to realize continuous detection of low cerebral blood flow. Sixty-three acutely brain injured patients with ICP monitoring, daily (133)Xenon cerebral blood flow (CBF) and daily transcranial Doppler (TCD) assessments were studied. Their ICP recordings were time-aligned with the CBF and TCD measurements so that a 1 h ICP segment near the CBF and TCD measurements was obtained. Each of these recordings was processed by the Morphological Cluster and Analysis of Intracranial Pressure (MOCAIP) algorithm to extract pulse morphological metrics. Then the differential evolution algorithm was used to find the optimal combination of the metrics that provided, using the regularized linear discriminant analysis, the largest combined positive predictivity and sensitivity. At a CBF threshold of 20 ml/min/100 g, a sensitivity of 81.8 +/- 0.9% and a specificity of 50.1 +/- 0.2% were obtained using the optimal combination of conventional TCD and blood analysis metrics as input to a regularized linear classifier. However, using the optimal combination of the MOCAIP metrics alone we were able to achieve a sensitivity of 92.5 +/- 0.7% and a specificity of 84.8 +/- 0.8%. Searching the optimal combination of all available metrics, we achieved the best result that was marginally better than those from using MOCAIP alone. This study demonstrated that the potential role of ICP monitoring may be extended to provide an indicator of low global cerebral blood perfusion.

Morphological clustering and analysis of continuous intracranial pressure

The continuous measurement of intracranial pressure (ICP) is an important and established clinical tool that is used in the management of many neurosurgical disorders such as traumatic brain injury. Only mean ICP information is used currently in the prevailing clinical practice, ignoring the useful information in ICP pulse waveform that can be continuously acquired and is potentially useful for forecasting intracranial and cerebrovascular pathophysiological changes. The present study introduces and validates an algorithm of performing automated analysis of continuous ICP pulse waveform. This algorithm is capable of enhancing ICP signal quality, recognizing nonartifactual ICP pulses, and optimally designating the three well-established subcomponents in an ICP pulse. Validation of the proposed algorithm is done by comparing nonartifactual pulse recognition and peak designation results from a human observer with those from automated analysis based on a large signal database built from 700 h of recordings from 66 neurosurgical patients. An accuracy of 97.84% is achieved in recognizing nonartifactual ICP pulses. An accuracy of 90.17%, 87.56%, and 86.53% was obtained for designating each of the three established ICP subpeaks. These results show that the proposed algorithm can be reliably applied to process continuous ICP recordings from real clinical environment to extract useful morphological features of ICP pulses.

Amplitude and phase of cerebrospinal fluid pulsations: experimental studies and review of the literature

OBJECT

A recently developed model of communicating hydrocephalus suggests that ventricular dilation may be related to the redistribution of pulsations in the cranium from the subarachnoid spaces (SASs) into the ventricles. Based on this model, the authors have developed a method for analyzing flow pulsatility in the brain by using the ratio of aqueductal to cervical subarachnoid stroke volume and the phase of cerebrospinal fluid (CSF) flow, which is obtained at multiple locations throughout the cranium, relative to the phase of arterial flow.

METHODS

Flow data were collected in a group of 15 healthy volunteers by using a series of images acquired with cardiac-gated, phase-contrast magnetic resonance imaging. The stroke volume ratio was 5.1 +/- 1.8% (mean +/- standard deviation). The phase lag in the aqueduct was -52.5 +/-16.5 degrees and the phase lag in the prepontine cistern was -22.1 +/- 8.2 degrees. The flow phase at the level of C-2 was -5.1 +/- 10.5 degrees, which was consistent with flow synchronous with the arterial pulse. The subarachnoid phase lag ventral to the pons was shown to decrease progressively to zero at the craniocervical junction. Flow in the posterior cervical SAS preceded the anterior space flow.

CONCLUSIONS

Under normal conditions, pulsatile ventricular CSF flow is a small fraction of the net pulsatile CSF flow in the cranium. A thorough review of the literature supports the view that modified intracranial compliance can lead to redistribution of pulsations and increased intraventricular pulsations. The phase of CSF flow may also reflect the local and global compliance of the brain.

Dural port therapy

INTRODUCTION

Dural port therapy (DPT) is a chiropractic procedure which can be used effectively with Sacro-Occipital Technique (SOT) procedures and which uses the sacrum as a lever to influence and balance the spine and cranium by way of the meningeal system.

DISCUSSION

Rationale and research is presented to explain the basis behind DPT's method of affecting the craniospinal system and its relationship to the meninges. Though the procedure can be used with most conditions, DPT appears to be safe to use with osteoporotic conditions, fractured vertebrae, and other conditions where a "thrust" to the spine may be contraindicated. Basic methods of using DPT are presented along with alternative methods which can be applied when the basic methods are not sufficient.

CONCLUSION

DPT reduces sacral, spinal, and cranial dura meningeal tension, lesions, torque and stress, as well as dural sleeve vasomotor interference. The possibility that the doctor can influence the nervous system directly in such a powerful manner warrants further investigation.

Origin of subarachnoid cerebrospinal fluid pulsations: a phase-contrast MR analysis

Cerebrospinal fluid (CSF) pulsations result from change of blood volume in the closed craniospinal cavity. We used cine phase contrast MR analysis to determine whether spinal CSF pulsations result from spinal vascular pulsations or intracranial subarachnoid pulsations, whether intracranial CSF pulsations result from intracranial large arteries pulsations or cerebrovascular bed changes. We performed a quantified physiological mapping of CSF velocity waveforms along the craniospinal axis. Thirty-six volunteers participated in the study. MR acquisitions were obtained at the intracranial level, the upper, midcervical, cervicothoracic, mid thoracic, and/or the thoracolumbar levels. The temporal velocity information were plotted as wave form and key temporal parameters were determined and analyzed; intervals from the R wave to the onset of CSF systole, to CSF systolic peak, to the end of systole, as well as duration of systole. Three kinds of dynamic channels could be differentiated along the spinal axis, the lateral, medioventral and mediodorsal channels. Lateral spinal CSF pulse waves show significant craniocaudal propagation. No such significant progression was detected through the medial channels along the spine. Through the medial channels, a cephalic progression was observed from the upper cervical level to the intracranial level. At the craniocervical junction, mediodorsal CSF systole appeared the earliest one whereas in the anterior intracranial basal cistern, CSF systole appeared delayed. In conclusion, spinal CSF pulsations seem to result mainly from intracranial pulsations in the lateral channels, whereas local vascular pulsations could modify CSF pulse wave mainly in the medial channels. At the craniocervical junction, our results suggest that blood volume change in the richly vascularised cerebellar tonsils is the main initiating factor of CSF systole; and that spinal vascular pulsations could be considered as an additional early and variable CSF pump.

Site of origin of spinal cerebrospinal fluid pulse wave

: Since vascular pulsation in the cerebrospinal fluid causes the cerebrospinal fluid pulse wave (CSFPW), spinal CSFPW may serve as a monitor of spinal cord blood flow. However, there are two possible sources of spinal CSFPW: brain and spinal cord pulsation, and it is unclear for which region spinal CSFPW provides blood flow information. To resolve this question, we analyzed changes in CSFPW caused by occlusion of the large vessels in mongrel dogs. The thoracic and abdominal aorta (TA group, n = 13; AA, n = 6), bilateral internal carotid arteries (ICA, n = 7), and superior and inferior vena cava (SVC, n = 6; IVC, n = 8) were occluded. The CSFPW was measured at the second cervical and sixth lumbar spine level. To eliminate the influence of hemodynamic changes caused by the occlusion, CSFPWs were decomposed into component frequencies, harmonic waves (HWs), and analyzed using the system analysis method. After occlusion, cervical CSFPW was decreased in groups ICA (change in the first HW, 38%; P < 0.05 by Wilcoxon signed-ranks test), TA (40%; P < 0.05), and SVC (53%; P < 0.05), while lumbar CSFPW was decreased in groups TA (71%; P < 0.01), AA (78%; P < 0.05), and IVC (48%; P < 0.05). These results show that spinal CSFPW provides information on the blood flow of a relatively localized region, and could be used to monitor spinal cord blood flow.

Retrospective estimation and correction of physiological fluctuation in functional MRI

Image-to-image fluctuation due to physiological motion is a major limitation to the accurate detection of neuronal activity with functional MRI. In this paper, a new and general technique for the estimation and compensation of the physiological effects is presented. By simultaneously monitoring the respiration and heart beat during the acquisition of imaging data, and retrospectively synchronizing the imaging data with physiological activity, physiological effects are estimated and removed. This technique does not rely on the periodicity of the respiration or the heart beat, does not affect the signal changes arising from neuronal activation, and is beneficial to images acquired with any speed. Experimental studies performed with FLASH and EPI sequences have demonstrated that the new technique is effective in reducing physiological fluctuation and improving the sensitivity of functional MRI and is generally applicable.

Characteristics of cerebrospinal fluid circulation in infants as detected with MR velocity imaging

Analysis of cerebrospinal fluid (CSF) flow and motion at the craniospinal junction was conducted by magnetic resonance velocity imaging with phase encoding followed by motion velocity integration. Thirteen normal subjects classified into two groups were studied: an infant group with open sutures and fontanel, and a noninfant group with closed sutures and fontanel. Predominance in CSF to-and-fro motion was recognized in the ventral subarachnoid space, and a maximum caudad motion velocity of 7.5 +/- 2.4 mm/s was recorded in the infant group and one of 14.9 +/- 6.2 mm/s in the noninfant group. The average bulk flow velocity in all cases was 86.7 +/- 81.6 (means +/- SD) mm/min. The difference in flow velocity between the infant group (19.7 +/- 28.2 mm/min) and the noninfant group (116.5 +/- 80 mm/min) suggested that the CSF circulation around the cervical spine may vary at different ages.

A quantitative analysis of cerebrospinal fluid flow in post-traumatic syringomyelia

Cerebrospinal fluid (CSF) flow within the syrinx in post-traumatic syringomyelia was studied by cardiac-triggered phase images of magnetic resonance imaging (MRI) to investigate the relationship between CSF flow in the syrinx and patients' symptoms.

Color Doppler flow imaging of CSF flow in infants with intracranial hemorrhage

The color Doppler flow imaging (CDFI) technique was used to study the dynamics of cerebrospinal fluid (CSF) flow in 13 infants with intracranial hemorrhage. CDFI was performed 46 times in 6 intraventricular hemorrhage (IVH) patients and 7 subarachnoid hemorrhage (SAH) patients with or without subdural hemorrhage during different stages. CSF flow was observed in 8 infants with IVH (5) or SAH (3) on CDFI. CSF flow in the aqueduct, third ventricle and foramen of Monro was visualized in both the upward and downward directions, primarily reflecting respiration and/or cardiac pulsation in the acute stage. It is suggested that CDFI may allow evaluation of the CSF flow dynamics and an early diagnosis of intracranial hemorrhage in infants.

Changes in cerebrospinal fluid pressure and spinal cord perfusion pressure prior to cross-clamping of the thoracic aorta in humans

Little is known about what influences cerebrospinal fluid pressure (CSFP) during anesthesia prior to aortic cross-clamping (AXC). Therefore, this study measured the effect of anesthetic induction, of various drugs administered during the course of surgery prior to AXC, and of hemodynamic changes on CSFP, and calculated spinal cord perfusion pressure (SCPP = mean arterial pressure [MAP] - CSFP) in 11 patients undergoing surgery on the descending thoracic aorta. A lumbar drainage catheter was placed to facilitate drainage of CSF and to measure CSFP. Anesthesia was induced with fentanyl, 50 micrograms/kg, and midazolam, 1 mg, using a pancuronium-metocurine mixture for neuromuscular blockade. Data were collected prior to and after (1) anesthetic induction, (2) mannitol to augment diuresis, (3) sequential use of sodium nitroprusside (SNP) and isoflurane (ISO) to lower MAP by 20%, (4) drainage of spinal fluid, (5) intrathecal injection of papaverine (IP), and (6) AXC. Statistical comparisons of recorded data were made using the least squares mean method and Friedman test. Linear regression was used to test for correlation between CSFP and hemodynamics. Anesthetic induction affected neither hemodynamics nor CSFP. Mannitol significantly increased heart rate, central venous pressure (CVP), pulmonary capillary wedge pressure (PCWP), cardiac output (CO), and CSFP (P less than 0.05). SNP or ISO altered neither CVP, PCWP, CO, nor CSFP, which remained elevated at the postmannitol infusion level. ISO, unlike SNP, caused a significant decrease in SCPP (P less than 0.005). Subsequent drainage of 20 mL of CSF improved SCPP (P less than 0.05). IP did not have any effect on hemodynamics or CSFP. CSFP showed a strong correlation with CVP (r = 0.86).(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in epidural pulse pressure in brain oedema following experimental focal ischaemia

This study was carried out to clarify the changes of pulse pressure of the intracranial pressure pulse wave in ischaemic brain oedema. Intracranial pressure and PP were measured in two groups of anaesthetized dogs; 1) increased volume of cerebrospinal fluid by cisternal saline injection (control group), 2) brain oedema caused by focal ischaemia (oedema group). Ischaemia was induced by 2 hours of occlusion of the anterior, middle cerebral and internal carotid arteries. The canine focal ischaemic model showed consistent ischaemic damage in the caudate nucleus and produced brain oedema successfully. PP increased linearly with rising ICP to 35 mm Hg, and PP in the oedema group was significantly smaller than that in the control group at the same ICP value. The slopes of the regression equation of ICP and PP were significantly different between the oedema and control group (oedema: 0.057 +/- 0.029, control: 0.106 +/- 0.009), mean +/- SD, P less than 0.005). These results suggest that PP is easily affected by ischaemic brain oedema, which indicates increase of the brain tissue in the cranium. We conclude that PP is affected even at the same ICP value when intracranial components have altered.

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.

Otologic manifestations of benign intracranial hypertension syndrome: diagnosis and management

Benign intracranial hypertension (BIH) is a syndrome characterized by increased intracranial pressure (IIP) without focal signs of neurological dysfunction. The diagnosis is essentially made by exclusion of various causes of IIP. The classic presenting symptoms of BIH are headache and/or visual disturbances. Otologic manifestations of this syndrome have not been described in detail. In this thesis, 20 BIH patients with associated otologic symptoms were thoroughly studied over a 5-year period. The author concludes that 1. objective pulsatile tinnitus and low frequency hearing loss can be the major or only manifestation of this syndrome; 2. diagnosis is established by lumbar puncture and elimination of other causes of IIP; 3. medical management is very effective with surgery reserved for patients with deteriorating vision or with disabling tinnitus.

Spectral analysis of the CSF pulse wave at different locations in the craniospinal axis

The frequency spectrum and the amplitude transfer function from arterial pulse pressure to the CSF pulse wave were estimated in the lateral ventricle, cisterna magna and lumbar subarachnoid space of anaesthetised ventilated cats under various conditions: (a) normal status, (b) inhalation of 5% CO2 and (c) saline infusion into the CSF space (0.045 ml/min). The CSF pulse waveforms in the lateral ventricle and cisterna magna were almost identical in all conditions. Inhalation of CO2 and saline infusion increased the values of the amplitude transfer function from blood pressure to the CSF pulse wave in the lateral ventricle and cisterna magna to a similar extent. The CSF pulse in the lumbar sac was remarkably damped under both normal conditions and during CO2 inhalation, but the damping was diminished by saline infusion. During the saline infusion, the spinal canal appeared to function as a low-pass filter to the conduction of the CSF pulse.

Spinal cord infarction in disease and surgery of the aorta

Diseases of the aorta and surgery of the aorta can produce spinal cord damage. There are major variations in blood supply to the spinal cord between individuals. The spinal cord may be tamponaded by increased spinal fluid pressure subsequent to clamping the aorta. Both of these factors may contribute to spinal cord infarction. The available methods and procedures to protect the spinal cord during surgery are discussed.

Otologic symptoms and findings of the pseudotumor cerebri syndrome: a preliminary report

Pseudotumor cerebri or benign intracranial hypertension is a syndrome characterized by increased intracranial pressure without focal signs of neurologic dysfunction. The clinical manifestations of this syndrome are usually headache and/or disturbance of vision. Although tinnitus, hearing loss, and vertigo have been described in association with intracranial hypertension, otologic symptomatology as the presenting manifestation of this syndrome has not been previously reported. In this article we report the otologic symptoms and findings of two pseudotumor cerebri patients, one of whom presented with pulsatile tinnitus. The pathogenesis of the otologic symptoms, diagnostic workup, and management of these patients are discussed.

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.

Diagnosis of hydrocephalus by CSF pulse-wave analysis: a clinical study

Pulsatility of the cerebrospinal fluid (CSF) is augmented in hydrocephalus. Analysis of pulsatility, including the CSF waveform, may be a more valid criterion for the diagnosis of hydrocephalus than mean CSF pressure. To test this possibility, CSF pressures were measured in 118 patients with presumed hydrocephalus. The pressure measurements included baseline mean pressure and pulse pressure, responses to jugular compression, and CSF wave analysis (amplitude and peak latency). Four groups of pressure recordings were identified and matched with four clinical groups: normal, arrested hydrocephalus, communicating hydrocephalus, and aqueduct stenosis hydrocephalus. The CSF pulse pressure and systolic slope form were highly reliable in the diagnosis of hydrocephalus, whereas mean CSF pressure was not reliable.

Experimental hydrocephalus following mechanical increment of intraventricular pulse pressure

Experimental hydrocephalus has been induced in lambs by artificial increase of the amplitude of intraventricular cerebrospinal fluid (CSF) oscillations related to arterial pulsations, without concomitant changes of the mean CSF-pressure. The characteristics of this hydrocephalus demonstrate that the intraventricular CSF-pulsations can play a role in the genesis of ventricular dilation. Such a method may be used to produce an original model of hydrocephalus independent of changes of CSF-circulation or absorption.

Influence of systemic and cerebral vascular factors on the cerebrospinal fluid pulse waves

In anesthetized, artificially ventilated dogs, the intracranial cerebrospinal fluid (CSF) pulse waves were studied simultaneously with the central aortic pressure, central venous pressure (CVP), and the sagital sinus pressure under physiological conditions and in normovolemic arterial hypotension and hypertension, in acute cardiac insufficiency of the right atrium, in raised intracranial pressure (ICP), and in arterial hypoxemia. The physiological CSF pulsations are shown to be mainly arterial in origin. In the diastolic phase, the descending part of the pulse curve can be modified by venous superpositions coinciding with the right atrial "A" wave. With increase of ICP the configuration of the CSF pulsations changes: the venous superpositions disappear and the waves become more and more arterial in shape. Furthermore, the pulse amplitude increases considerably. The same change can be observed when cerebral vessels are dilated by arterial hypoxemia. During cardiac insufficiency and consecutive increase of CVP, the CSF pulse curve is venous in shape and the right atrial "A" wabe predominates. In arterial hypotension, CSF pressure decreased. Conversely, in angiotensin-induced systemic arterial hypertension, CSF pressure and its pulse amplitude increased. It is concluded that both systemic arterial blood pressure and cerebrovascular reactivity are major determinants for the shape and the pressure amplitude of the intracranial CSF pulse waves. In the presence of cerebral vasodilatation, systemic arterial blood pressure may be an important factor in raising ICP and altering the brain tissue compliance, because cerebral vascular damping of the arterial pulse is diminished and the arterial pressure head may be directly transmitted to the cerebral capillary bed.