Significant Association of Slow Vasogenic ICP Waves with Normal Pressure Hydrocephalus Diagnosis

Brain blood flow pulse analysis may help to recognize individuals who suffer from hydrocephalus

BACKGROUND

Normal pressure hydrocephalus (NPH) is often associated with altered cerebral blood flow. Recent research with the use of the ultrasonic method suggests specific changes in the shape of cardiac-related cerebral arterial blood volume (CaBV) pulses in NPH patients. Our study aims to provide a quantitative analysis of the shape of CaBV pulses, estimated based on transcranial Doppler ultrasonography (TCD) in NPH patients and healthy individuals.

METHODS

The CaBV pulses were estimated using TCD cerebral blood flow velocity signals recorded from probable NPH adults and age-matched healthy individuals at rest. The shape of the CaBV pulses was compared to a triangular shape with 27 similarity parameters calculated for every reliable CaBV pulse and compared between patients and volunteers. The diagnostic accuracy of the most prominent parameter for NPH classification was evaluated using the area under the receiver operating characteristic curve (AUC).

RESULTS

The similarity parameters were calculated for 31 probable NPH patients (age: 59 years (IQR: 47, 67 years), 14 females) and 23 healthy volunteers (age: 54 years (IQR: 43, 61 years), 18 females). Eighteen of 27 parameters were different between healthy individuals and NPH patients (p < 0.05). The most prominent differences were found for the ascending slope of the CaBV pulse with the AUC equal to 0.87 (95% confidence interval: 0.77, 0.97, p < 0.001).

CONCLUSIONS

The findings suggest that in NPH, the ascending slope of the CaBV pulse had a slower rise, was more like a straight line, and generally was less convex than in volunteers. Prospective research is required to verify the clinical utility of these findings.

Intracranial pressure analysis software: A mapping study and proposal

Introduction Intracranial pressure (ICP) monitoring and analysis are techniques that are, each year, applied to millions of patients with pathologies with million of patients annually. The detection of the so called A and B-waves, and the analysis of subtle changes in C-waves, which are present in ICP waveform, may indicate decreased intracranial compliance, and may improve the clinical outcome. Despite the advances in the field of computerized data analysis, the visual screening of ICP continues to be the means principally employed to detect these waves. To the best of our knowledge, no review study has addressed automated ICP analysis in sufficient detail and a need to research the state of the art of ICP analysis has, therefore, been identified. Methodology This paper presents a systematic mapping study to provide answers to 7 research questions: publication time, venue and source trends, medical tasks undertaken, research methods used, computational systems developed, validation methodology, tools and systems employed for evaluation and research problems identified. An ICP software prototype is presented and evaluated as a consequence of the results. Results A total of 23 papers, published between 1990 and 2020, were selected from 6 online databases. After analyzing these papers, the following information was obtained: diagnosis and monitoring medical tasks were addressed to the same extent, and the main research method used was evaluation research. Several computational systems were identified in the papers, the main one being image classification, while the main analysis objective was single pulse analysis. Correlation with expert analysis was the most frequent validation method, and few of the papers stated the use of a published dataset. Few authors referred to the tools used to build or evaluate the proposed solutions. The most frequent research problem was the need for new analysis methods. These results have inspired us to propose a software prototype with which provide an automated solution that integrates ICP analysis and monitoring techniques. Conclusions The papers in this study were selected and classified with regard to ICP automated analysis methods. Several research gaps were identified, which the authors of this study have employed as a based on which to recommend future work. Furthermore, this study has identified the need for an empirical comparison between methods, which will require the use and development of certain standard metrics. An in-depth analysis conducted by means of systematic literature review is also required. The software prototype evaluation provided positive results, showing that the prototype may be a reliable system for A-wave detection.

RAQ: A Noise-Resistant Calibration-Independent Compliance Surrogate

The intracranial pressure (ICP)-volume relationship contains important information for diagnosing hydrocephalus and other space-occupying pathologies. We aimed to design a new parameter which quantifies the relationship and can be calculated from overnight recordings.The new parameter, the respiratory amplitude quotient (RAQ), characterizes the modulation of the pulse amplitude by the respiratory wave in the ICP time course. RAQ is defined as the ratio of the amplitude of the respiratory wave in the ICP signal to the amplitude of the respiration-induced wave in the course of the heartbeat-dependent pulse amplitude.We tested RAQ on synthetically generated ICP waveforms and found a mean difference of <0.5% between the calculated values of RAQ and the theoretically determined values. We further extracted RAQ from datasets obtained by overnight recording in hydrocephalus patients with a stenosis of the aqueduct and a comparison group finding a significant difference between the RAQ values of either group.

RAQ: a novel surrogate for the craniospinal pressure-volume relationship

OBJECTIVE

The intracranial pressure-volume relation contains information relevant for diagnostics of hydrocephalus and other space-occupying pathologies. We aimed to design a noise-resilient surrogate for this relationship that can be calculated from intracranial pressure (ICP) signals.

APPROACH

The new surrogate, termed respiratory amplitude quotient (RAQ), characterizes the modulation of the cardiac pulse wave amplitude by the respiratory wave in the ICP time course. RAQ is defined as the ratio of the amplitude of the respiratory wave in the ICP signal to the amplitude of the respiration-induced variation in the course of the cardiac pulse wave amplitude. We validated the calculation of RAQ on synthetically generated ICP waveforms. We further extracted RAQ retrospectively from overnight ICP recordings in a cohort of hydrocephalus patients with aqueductal stenosis, age 55.8 ± 18.0 years, and a comparison group with hydrocephalus diagnosed by morphology in MRI, but not responsive to either external lumbar drainage or ventriculo-peritoneal shunting, age 72.5 ± 6.1 years. RAQ was determined for the full recordings, and separately for periods containing B-waves.

MAIN RESULTS

We found a mean difference of less than 2% between the calculated values of RAQ and the theoretically determined equivalent descriptors of the synthetic ICP waveforms. In the overnight recordings, we found significantly different RAQ values during B-waves in the aqueductal stenosis (0.86 ± 0.11) and non-responsive hydrocephalus patient groups (1.07 ± 0.20), p = 0.027. In contrast, there was no significant difference in other tested parameters, namely pressure-volume index, elastance coefficient, and resistance to outflow. Neither did we find significant difference when considering RAQ over the full recordings.

SIGNIFICANCE

Our results indicate that RAQ may function as a potential surrogate for the intracranial pressure-volume relation.

Influence of mild-moderate hypocapnia on intracranial pressure slow waves activity in TBI

BACKGROUND

In traumatic brain injury (TBI) the patterns of intracranial pressure (ICP) waveforms may reflect pathological processes that ultimately lead to unfavorable outcome. In particular, ICP slow waves (sw) (0.005-0.05 Hz) magnitude and complexity have been shown to have positive association with favorable outcome. Mild-moderate hypocapnia is currently used for short periods to treat critical elevations in ICP. Our goals were to assess changes in the ICP sw activity occurring following sudden onset of mild-moderate hypocapnia and to examine the relationship between changes in ICP sw activity and other physiological variables during the hypocapnic challenge.

METHODS

ICP, arterial blood pressure (ABP), and bilateral middle cerebral artery blood flow velocity (FV), were prospectively collected in 29 adult severe TBI patients requiring ICP monitoring and mechanical ventilation in whom a minute volume ventilation increase (15-20% increase in respiratory minute volume) was performed as part of a clinical CO₂-reactivity test. The time series were first treated using FFT filter (pass-band set to 0.005-0.05 Hz). Power spectral density analysis was performed. We calculated the following: mean value, standard deviation, variance and coefficient of variation in the time domain; total power and frequency centroid in the frequency domain; cerebrospinal compliance (Ci) and compensatory reserve index (RAP).

RESULTS

Hypocapnia led to a decrease in power and increase in frequency centroid and entropy of slow waves in ICP and FV (not ABP). In a multiple linear regression model, RAP at the baseline was the strongest predictor for the decrease in the power of ICP slow waves (p < 0.001).

CONCLUSION

In severe TBI patients, a sudden mild-moderate hypocapnia induces a decrease in mean ICP and FV, but also in slow waves power of both signals. At the same time, it increases their higher frequency content and their morphological complexity. The difference in power of the ICP slow waves between the baseline and the hypocapnia period depends on the baseline cerebrospinal compensatory reserve as measured by RAP.

B waves: a systematic review of terminology, characteristics, and analysis methods

Background

Although B waves were introduced as a concept in the analysis of intracranial pressure (ICP) recordings nearly 60 years ago, there is still a lack consensus on precise definitions, terminology, amplitude, frequency or origin. Several competing terms exist, addressing either their probable physiological origin or their physical characteristics. To better understand B wave characteristics and ease their detection, a literature review was carried out.

Methods

A systematic review protocol including search strategy and eligibility criteria was prepared in advance. A literature search was carried out using PubMed/MEDLINE, with the following search terms: B waves + review filter, slow waves + review filter, ICP B waves, slow ICP waves, slow vasogenic waves, Lundberg B waves, MOCAIP.

Results

In total, 19 different terms were found, B waves being the most common. These terminologies appear to be interchangeable and seem to be used indiscriminately, with some papers using more than five different terms. Definitions and etiologies are still unclear, which makes systematic and standardized detection difficult.

Conclusions

Two future lines of action are available for automating macro-pattern identification in ICP signals: achieving strict agreement on morphological characteristics of “traditional” B waveforms, or starting a new with a fresh computerized approach for recognition of new clinically relevant patterns.

Current Updates on Idiopathic Normal Pressure Hydrocephalus

Idiopathic normal pressure hydrocephalus (iNPH) is one of the neurodegenerative diseases which can be treated surgically with favorable outcome. The gait disturbance, cognitive, and urinary symptoms are known as the clinical triad of iNPH. In this review, we have addressed the comorbidities, differential diagnoses, clinical presentations, and pathology of iNPH. We have also summarized the imaging studies and clinical procedures used for the diagnosis of iNPH. The treatment modality, outcomes, and prognosis were also discussed.