The patient alert system--pilot study of built-in warning systems for pacemakers.

Malfunction of a pacing system can be life-threatening for a pacemaker-dependent patient. It would be desirable for implantable pulse generators to have a built-in automatic warning system capable of alerting the patient as soon as a potentially dangerous disorder is detected. In this study, seven patients (mean age, 72.6 +/- 10.7 years) with slow, chronic atrial fibrillation underwent implantation of a dual-chamber pulse generator with a custom-made "alert electrode" connected to the atrial port of the pulse generator to stimulate the underlying pectoral muscle. The muscle was temporarily stimulated while the pacemaker was in VVIR mode. The lowest amplitude sufficient to alert the patient (perception threshold) was 1.6 +/- 0.58 V at 0.45 ms during implantation and 1.2 +/- 0.5 V at 0.45 ms chronically. In a second phase, alerts outside of the office were issued using a special software routine capable of delivering stimuli at programmable date and time.

A high-resolution large array (HRLA) surface EMG system.

A high-resolution large-array (HRLA) SEMG system comprising 256 separate channels has been developed. SEMG signals are detected by a "bracelet" active electrode array connected to a stack of newly designed biopotential instrumentation amplifiers. A stand-alone data logger acquires and stores the array EMG activity at high sampling rates. A RISC multiprocessor network supports computationally-intensive array signal processing and analysis algorithms. In addition, an improved optoelectronic system for the measurement of human body kinematics has been associated to the HRLA SEMG system to provide the related mechanical characteristics of muscle activity. Analysis results demonstrate that high-resolution muscle fibre conduction velocity histograms can be obtained even from skeletal muscles in which a large number of motor units are simultaneously activated.

Three-dimensional current density distribution under surface stimulation electrodes.

Overflow to non-target tissue during FNS can be reduced by controlling current density distribution under surface stimulating electrodes. A method is introduced for the acquisition of 3-D current density distributions under complex surface stimulating FNS electrode geometries. The method makes use of a phantom model in which a conventional homogeneous model has been improved by adding a layer to simulate skin impedance properties, based on specific FNS parameters. Signal acquisition and processing circuits have been developed to simulate the process by which excitable tissue responds to external stimulation. In addition, a data analysis method has been introduced to allow for the characterisation of stimulation current intensity, electrode geometry and pulse waveform required to achieve target muscle activation, with minimal overflow and to avoid pain or burning. Measurements of integrated differential voltage corresponding to current density distribution acquired under electrodes of various geometries are presented in terms of 3-D attenuation coefficient maps as examples of the applicability of the method.

New technologies for in-flight pasteless bioelectrodes.

Advances in development of in-flight electrophysiological-based systems such as G-LOC detectors, ECG-synchronized G-suits, and clinical monitors have dictated the need for pasteless electrodes that meet realistic operational demands and are suitable for the cockpit environment. New technologies appropriate for the design of bioelectrodes that meet these demands are described, including a stable dielectric electrode-skin interface material, miniaturized high-impedance electronics, and circuit fabrication methods. Design examples and resulting electrophysiological recordings are presented to demonstrate the new technologies.