ACT3: a high-speed, high-precision electrical impedance tomograph.

This paper presents the design, implementation, and performance of Rensselaer's third-generation Adaptive Current Tomograph, ACT3. This system uses 32 current sources and 32 phase-sensitive voltmeters to make a 32-electrode system that is capable of applying arbitrary spatial patterns of current. The instrumentation provides 16 b precision on both the current values and the real and reactive voltage readings and can collect the data for a single image in 133 ms.

Detection and imaging of electric conductivity and permittivity at low frequency.

This paper is concerned with low frequency electrical impedance imaging, which is the process of constructing images of the electrical impedance of a body's interior based upon measurements of voltage and current made at the body's surface. The electrical impedance accounts for both resistivity and permittivity. This paper shows how permittivity can be exploited to improve the performance of an electrical impedance imaging system.

Rapid assessment of electrode characteristics for impedance imaging.

Electrical impedance imaging is the technique for producing images of the resistivity of internal body structures based on measurements of voltage and current from electrodes applied to the body's surface. When a multiplicity of electrodes are applied in one or more rows around a body structure such as the thorax or limb, it is useful to be able to rapidly assess the general status of the electrode-body interface to determine if the skin has been suitably prepared, and that electrode and skin impedance are suitably low. In addition, assessment of the impedance of individual electrodes should precede acquisition of data for image formation.

Errors due to measuring voltage on current-carrying electrodes in electric current computed tomography.

Electric current computed tomography is a process for determining the distribution of electrical conductivity inside a body based upon measurements of voltage or current made at the body's surface. Most such systems use different electrodes for the application of current and the measurement of voltage. This paper shows that when a multiplicity of electrodes are attached to a body's surface, the voltage data are most sensitive to changes in resistivity in the body's interior when voltages are measured from all electrodes, including those carrying current.

Electrode models for electric current computed tomography.

This paper develops a mathematical model for the physical properties of electrodes suitable for use in electric current computed tomography (ECCT). The model includes the effects of discretization, shunt, and contact impedance. The complete model was validated by experiment.

Theory and performance of an adaptive current tomography system.

It has been shown that there exists an optimum set of current patterns for distinguishing one conductivity distribution from another. Since the optimum set of current patterns depends on the conductivity distribution being imaged it must be determined for each object being imaged. This paper describes how these current patterns may be determined and describes a system for achieving this in practice.

Current topics in impedance imaging.

We introduce a definition of 'best' currents to apply to an electrode array on the surface of a body in order to distinguish between the conductivity inside the body and a conjectured conductivity. Using these 'best' currents, we illustrate with a simple example the general fact that a single current applied between a pair of electrodes, loses its ability to distinguish between different conductivities as the size of the region over which the current is applied goes to zero. We next introduce approximations to the best currents on systems having L electrodes, and calculate the ability of these systems to distinguish between conductivities as L goes to infinity and the electrode size goes to zero.

A mobile physiological data acquisition system for clinical research.

The S.R. Powers Trauma Research Center at Albany Medical Center makes a wide variety of standard and specially designed physiological measurements on injured patients.

A system to measure functional residual capacity in critically ill patients.

The use of continuous positive airway pressure (CPAP) and intermittent mandatory ventilation (IMV) in spontaneously breathing, intubated patients has prompted the development of new procedures for measuring functional residual capacity (FRC). The authors have developed a system for measuring FRC by the multiple breath nitrogen washout technique, which is suitable for use on intubated patients breathing with CPAP, IMV, or intermittent positive pressure ventilation (CONTROL) and on nonintubated patients. This system uses a pair of synchronized volume ventilators to permit a step change in inspired N2 fraction while providing therapeutic ventilatory support.

An automatic sigh feature for animal ventilators.

A device is described that provides a reliable automatic deep breath to an animal being ventilated with a typical laboratory ventilator. The deep breath is provided by closing a solenoid valve in the expiratory tubing causing the animal to inspire two, three, or four consecutive tidal volumes without expiration. The interval between deep breaths is selected to be every 1, 2, 4, 6, 8, or 10 min.

In vitro characterization of the RP-6 dialyzer: co-current and counter-current clearance as a function of ultrafiltration.

Analytical and graphical techniques are described for presenting clearance data as a function of ultrafiltration; thus for the first time comparison of clearance values between dialyzers can be made unambiguously. This simple method uses a hand calculator to determine three coefficients. Clearance has been shown to be accurately described by the equation C = alpha 1 + alpha 2 Qv + alpha 3 (1/QBi).

A simple method for incorporating single pass dialysate delivery and controlled ultrafiltration with the RP-6 high flux dialyzer.

A simple hemodialysis protocol has been developed to permit significant "middle molecule" clearance, yet retain normal low molecular weight clearance. The high flux RP-6 dialyzer has been combined with a single pass dialysate delivery system to provide accurate control of ultrafiltration without resorting to specialized or expensive equipment. By operating the RP-6 in the co-current mode, a simple valve on the dialysate output can be used to regulate ultrafiltration.

Standards for accurate in vitro characterization of dialyzers: test case the Vivacell.

A standard format is proposed for cataloging dialyzer transport data in order to improve communication and understanding of published results. The need for such a format is obvious from the ambiguity and lack of uniformity in published data. This report for in vitro characterization also describes an adequate experimental set-up for proper dialyzer characterization and an improved means for reporting uncertainty where curve fitting techniques are employed.

Hyper/hypo-osmotic peritoneal dialysis.

This report concerns the augmentation of peritoneal dialysis using alternating hyper/hypoosmotic peritoneal dialysates, and covers a detailed examination of the longest lived, anephric goat to be maintained using this delivery system. Experimental results show that with this technique: 1) urea clearance can be increased some 200% over control values, 2) the convective transport of urea is unimportant and the increased urea clearance is due primarily to increased peritoneal permeability, 3) net ultrafiltration and electrolyte balance can be easily controlled by variation of total electrolyte and glucose about an appropriate mean. A detailed autopsy failed to demonstrate any gross or microscopic pathology.

Techniques of EEG frequency analysis for evaluation of uremic encephalopathy.

In an effort to provide nephrologists with practical, objective, and quantitative methods for evaluating uremic encephalopathy and the severity of uremia, we investigated five techniques for EEG frequency analysis, the selection of EEG samples for analysis, and the normal values for dominant frequency and the percent of EEG power from one through six Hz. The five techniques consisted of 1. handcounting, 2.