Influence of age on the relation between body position and noninvasively acquired intracranial pulse waves

The capacitive measurement of the head's dielectric properties has been recently proposed as a noninvasive method for deriving surrogates of craniospinal compliance (CC), a parameter used in the evaluation of space-occupying neurological disorders. With the higher prevalence of such disorders in the older compared to the younger population, data on the head's dielectric properties of older healthy individuals would be of particularly high value before assessing pathologic changes. However, so far only measurements on young volunteers (< 30 years) were reported. In the present study, we have investigated the capacitively obtained electric signal known as W in older healthy individuals. Thirteen healthy subjects aged > 60 years were included in the study. W was acquired in the resting state (supine horizontal position), and during head-up and head-down tilting. AMP, the peak-to-valley amplitude of W related to cardiac action, was extracted from W. AMP was higher in this older cohort compared to the previously investigated younger one (0°: 5965 ± 1677 arbitrary units (au)). During head-up tilting, AMP decreased (+ 60°: 4446 ± 1620 au, P < 0.001), whereas it increased during head-down tilting (- 30°: 7600 ± 2123 au, P < 0.001), as also observed in the younger cohort. Our observation that AMP, a metric potentially reflective of CC, is higher in the older compared to the younger cohort aligns with the expected decrease of CC with age. Furthermore, the robustness of AMP is reinforced by the consistent relative changes observed during tilt testing in both cohorts.

Queckenstedt's test repurposed for the quantitative assessment of the cerebrospinal fluid pulsatility curve

PURPOSE

Before the era of spinal imaging, presence of a spinal canal block was tested through gross changes in cerebrospinal fluid pressure (CSFP) provoked by manual compression of the jugular veins (referred to as Queckenstedt's test; QT). Beyond these provoked gross changes, cardiac-driven CSFP peak-to-valley amplitudes (CSFPp) can be recorded during CSFP registration. This is the first study to assess whether the QT can be repurposed to derive descriptors of the CSF pulsatility curve, focusing on feasibility and repeatability.

METHOD

Lumbar puncture was performed in lateral recumbent position in fourteen elderly patients (59.7±9.3 years, 6F) (NCT02170155) without stenosis of the spinal canal. CSFP was recorded during resting state and QT. A surrogate for the relative pulse pressure coefficient was computed from repeated QTs (i.e., RPPC-Q).

RESULTS

Resting state mean CSFP was 12.3 mmHg (IQR 3.2) and CSFPp was 1.0 mmHg (0.5). Mean CSFP rise during QT was 12.5 mmHg (7.3). CSFPp showed an average 3-fold increase at peak QT compared to the resting state. Median RPPC-Q was 0.18 (0.04). There was no systematic error in the computed metrics between the first and second QT.

CONCLUSION

This technical note describes a method to reliably derive, beyond gross CSFP increments, metrics related to cardiac-driven amplitudes during QT (i.e., RPPC-Q). A study comparing these metrics as obtained by established procedures (i.e., infusion testing) and by QT is warranted.

The effect of body position change on noninvasively acquired intracranial pulse waves

Objective. Craniospinal compliance (CC) is an important metric for the characterization of space-occupying neurological pathologies. CC is obtained using invasive procedures that carry risks for the patients. Therefore, noninvasive methods for acquiring surrogates of CC have been proposed, most recently based on changes in the head's dielectric properties during the cardiac cycle. Here, we have tested whether changes in body position, which are known to influence CC, are reflected in a capacitively acquired signal (hereinafter referred to as W) originating from dynamic changes of the head's dielectric properties. &#xD;Approach. Eighteen young healthy volunteers were included in the study. After 10 minutes in supine position, subjects were tilted head-up (HUT), back to 0° (horizontal, control), and then head-down (HDT). Metrics related to cardiovascular action were extracted from W, including AMP, the peak-to-valley amplitude of the cardiac modulation of W. Computational electromagnetic simulations were performed to probe the association between intracranial volume change and W. &#xD;Main results. AMP decreased during HUT (0°: 2869±597 arbitrary units (au); +75°: 2307±490 au, P=0.002) and increased during HDT (-30°: 4403±1428 au, P<0.0001). The same behavior was predicted by the electromagnetic model. &#xD;Significance. Tilting affects the distribution of CC between cranial and spinal compartments. Cardiovascular action induces compliance-dependent oscillatory changes in the intracranial fluid composition, which causes corresponding variations in the head's dielectric properties. These manifest as increasing AMP with decreasing intracranial compliance, which suggests that W may contain information related to CC, and that it might be possible to derive CC surrogates therefrom.

Theory for a non-invasive diagnostic biomarker for craniospinal diseases

Monitoring intracranial pressure (ICP) and craniospinal compliance (CC) is frequently required in the treatment of patients suffering from craniospinal diseases. However, current approaches are invasive and cannot provide continuous monitoring of CC. Dynamic exchange of blood and cerebrospinal fluid (CSF) between cranial and spinal compartments due to cardiac action transiently modulates the geometry and dielectric properties of the brain. The resulting impedance changes can be measured and might be usable as a non-invasive CC surrogate. A numerically robust and computationally efficient approach based on the reciprocity theorem was developed to compute dynamic impedance changes resulting from small geometry and material property changes. The approach was successfully verified against semi-analytical benchmarks, before being combined with experimental brain pulsation data to study the information content of the impedance variation. The results indicate that the measurable signal is dominated by the pulsatile displacement of the cortical brain surface, with minor contributions from the ventricular surfaces and from changes in brain perfusion. Different electrode setups result in complementary information. The information content from the investigated three electrode pairs was employed to successfully infer subject-specific brain pulsation and motion features. This suggests that non-invasive CC surrogates based on impedance monitoring could be established.

Noninvasive Monitoring of Intracranial Pulse Waves

OBJECTIVE

The clinical management of several neurological disorders benefits from the assessment of intracranial pressure and craniospinal compliance. However, the associated procedures are invasive in nature. Here, we aimed to assess whether naturally occurring periodic changes in the dielectric properties of the head could serve as the basis for deriving surrogates of craniospinal compliance noninvasively.

METHODS

We designed a device and electrodes for noninvasive measurement of periodic changes of the dielectric properties of the human head. We characterized the properties of the device-electrode-head system by measurements on healthy volunteers, by computational modeling, and by electromechanical modeling. We then performed hyperventilation testing to assess whether the measured signal is of intracranial origin.

RESULTS

Signals obtained with the device on volunteers showed characteristic cardiac and respiratory modulations. Signal oscillations can be attributed primarily to changes in resistive properties of the head during cardiac and respiratory cycles. Reduction of end-tidal CO₂, through hyperventilation, resulted in a decrease in the signal amplitude associated with cardiovascular action.

CONCLUSION

Given the higher CO₂ reactivity of intracranial vessels compared to extracranial ones, the results of hyperventilation testing suggest that the acquired signal is, in part, of intracranial origin.

SIGNIFICANCE

If confirmed in larger cohorts, our observations suggest that noninvasive capacitive acquisition of changes in the dielectric properties of the head could be used to derive surrogates of craniospinal compliance.

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.

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

OBJECTIVE

We aimed to test whether there is an association of slow vasogenic wave (SVW) occurrence with positive response to external lumbar drainage (ELD) and ventriculoperitoneal shunting and to design a method for the recognition and quantification of SVWs in the intracranial pressure (ICP) signal.

MATERIALS AND METHODS

We constructed SVW templates using normalized sine waves. We calculated the cross-correlation between the respective SVW template and the ICP signal. This was followed by shifting the templates forward and performing the cross-correlation analysis again until the end of the recording. Cross-correlation values above a threshold were considered to be indicative of SVWs. This threshold was previously determined and validated on a sample of ICP records of six patients. We calculated the root mean square of the recognized SVW periods as a measure of signal strength. Time-averaged signal strength was calculated over the full recording time (ICP_Smean) and over the wave periods (ICP_S).

RESULTS

We determined ICP_S and ICP_Smean in recordings of 2 groups of patients presenting with Hakim's triad: 26 normal pressure hydrocephalus (NPH) patients and 20 non-NPH patients. We then tested whether there was an association between ICP_S or ICP_Smean and the respective diagnosis using a Mann-Whitney test. We found significant association between ICP_S (p = 0.014) and ICP_Smean (p = 0.022) and the diagnoses.

CONCLUSIONS

The described method based on pattern recognition in the time domain is suitable for the detection and quantification of SVWs in ICP signals. We found a significant association between the occurrence of SVWs and independent NPH diagnosis.

Magnetic microparticles for endovascular aneurysm treatment: in vitro and in vivo experimental results

OBJECTIVE

Endovascular treatment of intracranial aneurysms employing endosaccular coiling can be associated with aneurysm perforation, coil herniation or incomplete obliteration fueling the interest to investigate novel endovascular techniques. We aimed to test a novel embolization material in experimental aneurysms in vitro and in vivo whereby intra-arterially administered magnetic microparticles (MMPs) are navigated into the lumen of vascular aneurysms with assistance from an external magnetic field.

METHODS

MMPs are core-shell particles suspended in saline that have a shell made of a polymeric material and a core made of magnetite (Fe3O4). They have a diameter of 1.4 μm. During MMP administration via a microcatheter, a magnetic field was applied externally to direct the particles with the use of a solid-state neodymium magnet. Experiments were performed in a perfused silicone vessel and aneurysm model to evaluate application techniques and fluid dynamics and in the elastase aneurysm model in rabbits to evaluate in vivo compatibility, including multiorgan histological examinations and long-term stability of aneurysm embolization.

RESULTS

It was possible to steer and hold the MMPs within the aneurismal cavity where they occluded the lumen progressively. After removal of the external magnetic field, the results remained stable in vivo for the remainder of the observational period (30 minutes); after a 12-week observational period, recanalization of the aneurysm occurred.

CONCLUSION

MMPs can be magnetically directed into aneurysms, allowing short-term obliteration. Although the method has yet to show reliable long-term stability, these experiments provide proof of concept, encouraging further investigation of intravascular magnetic compounds.

Mounting device for external cerebrospinal fluid drainage: the Freiburg Stativ

BACKGROUND

External drainage of cerebrospinal fluid (CSF) is one of the most common neurosurgical procedures. It is important to maintain a stable drainage rate, but with the commonly available mountings for CSF drainage this can be difficult to achieve. The drainage rate is dependent on the height-difference between the CSF space and the drip chamber of the device. Most mountings for open CSF drainage cannot be satisfactorily fixed at the bed of the patient; especially if the head of the bed is moved, there is a risk of over- or underdrainage.

MATERIALS AND METHODS

We have therefore constructed a mounting for open CSF drainage which allows appropriate adjustment of the rate of CSF outflow, even if the patient's head part of the bed is moved.

FINDINGS

The device was easily mountable or exchangeable at any hospital bed and served equally well for ventricular or for lumbar drainage.

CONCLUSION

We think that this device can help to reduce serious complication of over- or underdrainage in external CSF drainage.

Genetically modified maize and soybean on the Egyptian food market

The results of a survey study on food samples produced from genetically modified soybean and maize collected from the Egyptian market are presented. Forty samples of soybean and 40 samples of maize products have been gathered randomly from markets in Cairo and Giza. The genetic modification was detected by polymerase chain reaction (PCR) using official detection methods according to section 35 of the German Foodstuffs Act. Samples were investigated for the presence of material derived from the following genetically modified organisms (GMOs) all of which are approved for food use in Europe: Roundup Ready soybean (RRS) and maize lines Bt176, Bt11, T25 and MON810. In addition, samples were examined in qualitative and quantitative analysis for the presence of material derived from the transgenic maize line StarLink (Aventis) which was approved for animal feed use exclusively in the US. Twenty % of 40 investigated soy samples contained Roundup Ready soybean; 15% of 40 maize samples tested positive for Bt176 and 12.5% positive for Bt11 maize. Furthermore, the presence of StarLink maize could clearly be demonstrated in four samples mixed with Bt176 and Bt11. The percentage of StarLink was less than 1% in quantitative analysis. The maize lines T25 and MON810 were not detected.

Ovalis TAH: development and in vitro testing of a new electromechanical energy converter for a total artificial heart

A new electromechanical energy converting system has been developed to yield an efficient and durable orthotopic total artificial heart (TAH). The energy converter we developed transforms the unidirectional rotational motion of the motor into a longitudinal forward-reverse movement of an internal geared oval, linked directly to pusher plates on both sides. To ensure a permanent positive connection between the drive gear and the internally geared wheel, a ball bearing runs inside an oval shaped guide track. Motor, gear unit, and conical pusher plates are seated between alternately ejecting and filling ventricles. The unidirectional motion of the brushless DC motor affords easier motor control, reduces energy demand, and ensures longer life of the motor when compared with a bidirectional motion system. In vitro testing has been performed on a mock circulation loop. The overall system efficiency of the TAH Ovalis was 27-39% (mean, 36%) for the pump output range of 2-7 L/min. The maximum output of 7 L/min can be obtained with a pump rate of 130 min(-1) and an afterload pressure of 140 mm Hg. For an average sized human with a mean cardiac output of 6 L/min at a mean aortic pressure of 120 mm Hg, 5 watts of input power would be required. The size of the prototype is 560 cm3, the weight is 950 g. Our first in vitro studies demonstrated the excellent efficiency and pump performance of this new electromechanical energy converter. The results prove the feasibility of this new concept's use as an energy converter for a total artificial heart.

A comparative study of the Spiegelberg compliance device with a manual volume-injection method: a clinical evaluation in patients with hydrocephalus

A new automated method of compliance measurement has been developed which may overcome some of the problems of the manual method. Measurement of craniospinal compliance in brain-injured patients offers the potential for early detection of raised intracranial pressure (ICP) before it rises to levels that may damage brain parenchyma. However, limitations of the existing manual volume pressure techniques have meant few centres routinely perform compliance testing. We report on the results of testing this new method against a manual volume pressure response method (VPR) in 10 patients with hydrocephalus. In this comparison study, 19 pairs of compliance measurements were obtained from 10 patients. The compliance values obtained ranged from 0.141 to 1.407 ml/mmHg. There was a good correlation between the two methods (r2 = 0.8508). The average bias in compliance between the two methods was 0.111 ml/mmHg (95% CL for the bias = 0.0438, 0.1788) with the new method reading higher compliance than the manual method. These results indicate that the new automatic method of compliance measurement correlates well with an independent and classical measurement of compliance, and defines the bias and limits of agreement by which the new method measures craniospinal compliance in patients with hydrocephalus. Further work is needed to validate this device over a wider compliance range, especially at the lower compliance range often found in head injured patients. Studies are also required to determine the normal range of compliance values in the patient populations who undergo ICP monitoring. Research into determining which patient populations may benefit from continuous compliance measurement is warranted.

Evaluation of a gas chromatographic method to identify irradiated chicken, pork, and beef by detection of volatile hydrocarbons

A method suitable for routine application was used in an interlaboratory study to detect irradiation treatment of chicken carcass, pork, and beef. By using gas chromatographic analysis, 17 participating laboratories determined the quantity of 4 different radiation-induced volatile hydrocarbons (tetradecene, pentadecane, hexadecadiene, and heptadecene) in the fat fraction of coded specimens approximately 3 and 6 months after irradiation. The specimens of each type of meat were supplied by 2 different producers. The dose range tested (0.6-7.5 kGy) included levels commercially used to reduce the number of contaminating microorganisms (1-5 kGy). The method employed permitted a correct identification of irradiated or nonirradiated in 98.3% of the 864 specimens.

[Identification of irradiated pasteurized egg products: a combined method for use in routine control]

Pasteurized egg products (whole egg, egg yolk and egg white) were tested for irradiation treatment in the German food control laboratories in Oldenburg/Niedersachsen and Kassel/Hessen as well as in the food irradiation laboratory of the German federal health office. Gas chromatographic/mass spectrometric measurements on the fat components of egg-products showed clearly whether the product had been irradiated or not. While in unirradiated samples no traces of special hydrocarbons (according to the fatty acid composition of egg) and no traces of the irradiation-specific compound 2-Dodecyl-cyclobutanone were found, irradiated control samples as well as products of two Belgian suppliers contained these substances. Additionally, regarding the rather high time consumption of gas chromatography, electron spin resonance (ESR)-measurements were carried out on the packaging material of egg products. Irradiated packaging material (cellulose) could be easily detected by the appearance of a signal pair in the ESR spectrum (cellulose radical). ESR measurements are very fast and easy to perform so that this method can be used for screening. Microbiological investigations showed remarkably reduced total numbers of microorganisms for some irradiated samples, but the microbiological status is influenced by other factors like storage-time and -temperature, so that microbiological tests can not be used successfully for screening on irradiation treatment.

Assessment of electrophoretic mobility changes of human erythrocytes by free flow electrophoresis after in vitro and in vivo irradiation

Single cell measurements of electrophoretic mobility showed a linear dose-response of human erythrocytes after exposure to ionizing radiation. To establish a biological indicator- or dosimeter-system for application to dose-estimations after accidental exposures, we tried to measure dose dependent EPM-changes by the free flow electrophoresis technique, a rapid and efficient method which supplies the capacity needed for application. The in vitro irradiated erythrocytes of most donors showed an oscillating dose-response but erythrocytes from several other individuals in a contradictory manner whereby the EPM of erythrocytes from radiotherapy patients increased linearly with the amount of administered dose. However, the wide interindividual EPM-range of unirradiated erythrocytes inhibits the application of this technique in biological dosimetry.

Changes in oligosaccharides of human blood cells measured by tritium- and FITC-labeled lectins after in vitro- and in vivo-irradiation--lectin binding as a 'biological dosemeter'?

The lectin-binding system has been described previously as a biological dosimeter, by revealing induced changes in oligosaccharides of the cell membrane. The measurements were performed by binding [3H]concanavalin A to blood cells. Our results on human blood cells irradiated in vitro with doses in the range 0.5-5 Gy indicate great difficulties in using radioactive labeled Con-A for an accurate quantitative analysis of radiation effects on cell membranes. It appears nearly impossible to differentiate between only a few damaged cells and the remaining undamaged cells. Using fluorescein-labeled Con-A and wheat germ agglutinin, single-cell measurements of fluorescence intensity by flow cytometry revealed enhanced lectin-binding to platelets, lymphocytes and monocytes in the dose range 0.5-5 Gy after in vitro irradiation. But even by this method it was impossible to discriminate irradiations in either partial or whole-body irradiated patients. There were no significant or reproducible changes in the binding capacities of the blood-cell membranes of these patients. Therefore, the suitability of lectin binding as a 'biological indicator' for irradiation could not be confirmed.

[X-linked night-blindness: clinical and electrophysiological investigations including de-ERG in two families (author's transl)]

Patients from two families with X-linked recessive nyctalopia and myopia were investigated. The functional tests included clinical examinations (visual acuity, color sense, visual fields, dark adaptation) and electrophysiological examinations (ac coupled ERG, dc-coupled ERG, EOG). The dc-coupled ERG registrations were done without general anesthesia. In one case, a comparison with results obtained in 1967 was possible. There was no evidence of increase in functional impairment. On the basis of the electrophysiological results, the nature and localization of the defect causing nyctalopia are discussed. The postreceptoral retinal structures appear not to be involved exclusively.