A method for pneumatically inserting an array of penetrating electrodes into cortical tissue

The goal of this research was to find a practical means by which an array of 100 needle-shaped electrodes could be implanted into the cerebral cortex with minimal brain tissue trauma. It was found that insertion of these structures into cortical tissues could only be performed using high insertion speeds. A pneumatically actuated impact insertion system has been developed that is capable of inserting an electrode array into feline brain tissue at speeds from about 1 to 11 m/s. We found that a minimum array insertion speed of 8.3 m/s was necessary for a complete, safe insertion of all 100 electrodes in the array to a depth of 1.5 mm into feline cortex. The performance of the impact insertion system is discussed in terms of a simplified representation of cortical tissue.     

A new intelligent terminal for clinical computer network

An intelligent terminal has been developed to provide the clinical staffs with a means of utmost simplicity to communicate with the computer. Only 16 keys and a single switch are all which are involved in any terminal operation. The members of the operating system are the interpreter of TEXTOR (a language developed in this study), editor, monitor, and data-communication handler. This system configuration greatly reduces the cost for data communication compared with the conventional communication systems.     

Influence of measurement noise and electrode mislocalisation on EEG dipole-source localisation

Measurement noise in the electro-encephalogram (EEG) and inaccurate formation about the locations of the EEG electrodes on the head induce localisation errors in the results of EEG dipole source analysis. These errors are studied by performing dipole source localisation for simulated electrode potentials in a spherical head model, for a range of different dipole locations and for two different numbers (27 and 148) of electrodes. Dipole source localisation is performed by iteratively minimising the residual energy (RE), using the simplex algorithm. The ratio of the dipole localisation error (cm) to the noise level (%) of Gaussian measurement noise amounts to 0.15 cm/% and 0.047 cm/% for the 27 and 148 electrode configurations, respectively, for a radial dipole with 40% eccentricity The localisation error due to noise can be reduced by taking into account multiple time instants of the measured potentials. In the case of random displacements of the EEG electrodes, the ratio of dipole localisation errors to electrode location errors amounts to 0.78 cm⁻¹ cm and 0.27 cm⁻¹ cm for the 27 and 148 electrode configurations, respectively. It is concluded that it is important to reduce the measurement noise, and particularly the electrode mislocalisation, as the influence of the latter is not reduced by taking into account multiple time instants.     

BBB leakage,astrogliosis, and tissue loss correlate with silicon microelectrode array recording performance

The clinical usefulness of brain machine interfaces that employ penetrating silicon microelectrode arrays is limited by inconsistent performance at chronic time points. While it is widely believed that elements of the foreign body response (FBR) contribute to inconsistent single unit recording performance, the relationships between the FBR and recording performance have not been well established. To address this shortfall, we implanted 4X4 Utah Electrode Arrays into the cortex of 28 young adult rats, acquired electrophysiological recordings weekly for up to 12 weeks, used quantitative immunohistochemical methods to examine the intensity and spatial distribution of neural and FBR biomarkers, and examined whether relationships existed between biomarker distribution and recording performance. We observed that the FBR was characterized by persistent inflammation and consisted of typical biomarkers, including presumptive activated macrophages and activated microglia, astrogliosis, and plasma proteins indicative of blood-brain-barrier disruption, as well as general decreases in neuronal process distribution. However, unlike what has been described for recording electrodes that create only a single penetrating injury, substantial brain tissue loss generally in the shape of a pyramidal lesion cavity was observed at the implantation site. Such lesions were also observed in stab wounded animals indicating that the damage was caused by vascular disruption at the time of implantation. Using statistical approaches, we found that blood–brain barrier leakiness and astrogliosis were both associated with reduced recording performance, and that tissue loss was negatively correlated with recording performance. Taken together, our data suggest that a reduction of vascular damage at the time of implantation either by design changes or use of hemostatic coatings coupled to a reduction of chronic inflammatory sequela will likely improve the recording performance of high density intracortical silicon microelectrode arrays over long indwelling periods and lead to enhanced clinical use of this promising technology.     

Influence of the N-methyl- -aspartate antagonist memantine on human motor cortex excitability

The aim of our study was to investigate the effect of the N-methyl- -aspartate (NMDA) antagonist memantine on motor excitability in humans. Seven healthy volunteers received memantine or placebo, respectively, over a period of 8 days. At day 8, transcranial magnetic stimulation (TMS) was performed using a paired pulses paradigm in order to assess intracortical inhibition and facilitation. Additionally, motor threshold and silent period duration after TMS were measured as well as M waves, F waves and peripheral silent period after electrical peripheral nerve stimulation. Intracortical inhibition was enhanced, and intracortical facilitation reduced after memantine ingestion in comparison to placebo, whereas no significant difference could be observed regarding the other neurophysiological parameters. We conclude that the NMDA receptor is involved in the regulation of excitability of intracortical interneuronal circuits.     

A multi-channel stimulator and electrode array providing a rotating current whirlpool for electrical stimulation of wounds

When electrical stimulation is used on wounds, the electrical current has difficulty penetrating areas where there is necrotic tissue. Further, for an irregularly shaped wound, current distribution is poor in some areas of the wound since conventional two-electrode delivery systems provide the greatest current in a line directly between the electrodes. A new stimulator and electrode system is described which uses three electrodes spaced around a wound to disperse current more evenly. The stimulator senses tissue impedance and then redirects current by altering its Thevenin's output impedance for each electrode; each of the three electrodes becomes the active one in sequence while the remaining are the sink electrodes. Eight subjects were examined to test the stimulator. Electrical stimulation was applied to the skin above the quadriceps muscle at currents of 15 mA in six subjects without wounds and in two subjects with wounds. The relationship between electrode position and current dispersion on the skin was examined with a two-electrode vs. a three-electrode system to set stimulation parameters for the computer. The results showed that the three-electrode system could (1) detect areas of the skin with high impedance; (2) compensate by altering the Thevenin's output impedance at each of the three electrodes to shift current to high impedance areas; (3) provide uniform current across the skin as assessed by skin current and blood flow measurements with a laser Doppler flow imager.     

Engineering methods for monitoring the proper localization of muscle and cardial electrodes during cardiomyoplasty operation

Methods are elaborated for monitoring the localisation of muscle and cardiac electrodes during cardiomyoplasty operation. The necessary operation testing system is devised. The paper presents the results of the monitoring of 42 cardiomyoplasty operations with implantation of Stiminak-805 and EKS-445 electrostimulators. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 117, N ^o , 3, pp. 325–328, March, 1994 Presented by V. I. Burakovskii, Member of the Russian Academy of Medical Sciences     

Glutamate-induced disturbances in neurotransmission and ionic homeostasis of extracellular Ca2+ and K+ in CA1 hippocampal area

The effect of various concentrations ofl-glutamate on neurotransmission in the CA1 hippocampal area was studied using hippocampal slices. Three intervals ofl-glutamate concentration were established: ≤1 mM (all studied parameters are completely reversible upon washout, transmission being preserved), from 1 to 10 mM (both responses to frequency stimulation and single population spikes remain partially suppressed after washout), and above 10 mM (more than 50% suppression of transmission persists after washout). Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 124, No. 9, pp. 255–258, September, 1997     

Construction and performance of a new catheter-tip oxygen electrode

A membrane-covered catheter-tip oxygen-electrode system is described, which gives a linear response in the P_o2 range of 0–350 mm Hg. The system is highly stable, free from drift and mechanically safe for application in man. This is accomplished by using a screw cap for fastening the membrane holder, thus preventing the loss of parts and making the electrolyte chamber really fluidtight. Insulation of the platinum wire with glass precludes the possibility of fluid-bridge contact with the silver anode beyond the measuring site at the tip.     

Optimum electrode configuration for detection of arm movement using bio-impedance

A four-channel impedance measurement system, including a two-channel goniometer, to analyse human arm movement, was constructed. Impedances and joint angles were simultaneously measured for wrist and elbow movements. As the impedance changes resulting from wrist and elbow movements depended heavily on electrode placement, the optimum electrode configurations for those movements were determined by searching for high correlation coefficients, large impedance changes and minimum interferences in ten subjects (age: 29±6 years). The optimum electrode configurations showed very strong relationships between the wrist joint elbow joint angle and upper arm impedance (correlation coefficient=−0.97±0.03). Although the measured impedance changes of the wrist (1.1±1.5Ω) and elbow (−5.0±2.9Ω) varied between individuals, the reproducibilities of wrist and elbow impedance changes of five subjects were 5.8±1.8% and 4.6±1.4% for the optimum electrode pairs, respectively. It is proposed that this optimum electrode configuration would be useful for future studies involving the accurate measurement of arm movements by the impedance method.     

Development of a miniaturepH glass electrode with field-effect-transistor amplifier for biomedical applications

A miniaturepH glass electrode for possible clinical and biomedical applications was constructed and evaluated in referencepH buffer solutions at 36°C. A field-effect-transistor (f.e.t.) amplifier was integrated into the system, and its effectiveness was investigated. The average e.m.f. efficiency of the developed electrode was 0·87±0·11V, and a minimum length of 7 mm was required for a goodpH response. Temperature dependence of the electrode was ?1·51 mV/^oK at apH of 7. Evaluation of the stability of the electrode showed a 1% drift over a 7 h operational time. ThepH and temperature hysteresis effects showed 0·5% and 1·0% deviations, respectively. The response time was within 4 s for 99% response. These electrode characteristics were also investigated in blood plasma and discussed.     

Vascular interface system for automation of haemodynamic monitoring and therapy

A vascular interface system has been designed to relieve the bedside staff in the critical-care environment of time-consuming and unreliable manual operations. The system has made it possible to link a computer-based data acquisition system directly to the patient and provides for automatic haemodynamic monitoring and therapy. The vascular interface system provides access to the patient's vascular sites primarily through pneumatically operated valve assemblies which are biologically (blood) compatible. All connections between catheter and measuring instruments are short, transparent tubes which are easily visible for observation. Operation of the system is simplified through the use of push-button controls with each control assigned a specific procedure (e.g. pressure monitoring, catheter flush and cardiac output). Special safety features built into the system, such as manual override of valve control, ensure continuing operation despite power failure. The existence of the vascular interface system now allows the distribution of blood to a variety of online satellite systems at the bedside. The use of automated equipment frees vital personnel from time-consuming procedures and allows them to return to the real task of observation and patient care.     

Radioprotective action of lymphokinin,a composite preparation of cytokines

Lymphokinin injected into mice in a dose of 25,000 U/kg intraperitoneally before or after their single irradiation producing acute radiation sickness is found to prolong their survival. The optimal time for administering Lymphokinin depends on the radiation dose. Its survival-prolonging effect is most marked when it is injected 1 h or 24 h before or 23 h after exposure to a dose of 6.0 Gy. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 118, N ^o 7, pp. 38–40, July, 1994 Presented by N. N. Trapeznikov, Member of the Russian Academy of Medical Sciences