Forces consistent with plateau-like behaviour of spinal neurons evoked in patients with spinal cord injuries.

Percutaneous electrical stimulation over tibialis anterior and triceps surae was performed in 14 patients with traumatic spinal cord injury (SCI) to look for evidence that 'extra contractions' can develop, beyond those due to activation of the motor axons beneath the stimulating electrodes. Criteria for the extra contractions included marked asymmetry of force with respect to stimulation, progressively rising force during stimulation of constant amplitude and frequency, and force remaining high after stimulation frequency had returned to the control level following a high-frequency burst. Twelve of the 14 patients showed evidence of such behaviour, more frequently in triceps surae than tibialis anterior. Force or electromyographic activity commonly outlasted the stimulation in these patients. There was no apparent correlation between the completeness or level of injury and the ability to induce the behaviour. Evidence of force potentiation and 'habituation' was also seen. Eleven of the 14 patients exhibited hyper-reflexia and reported spontaneous spasms, but there was no obvious association with the extra contractions. It is concluded that non-classical behaviour of neurons within the spinal cord can contribute to the extra contractions evoked by electrical stimulation over muscles in spinal cord-injured subjects. This central contribution is less easy to obtain than in intact healthy subjects, all of whom showed the phenomenon. These contractions are consistent with the activation of plateau potentials in spinal neurons and, if so, plateau potentials may contribute to a patient's clinical manifestations.

Antibody responses to bacteriophage phi X-174 in human subjects exposed to the antarctic winter-over model of spaceflight.

BACKGROUND: It has been proposed that exposure to long-term spaceflight conditions (stress, isolation, sleep disruption, containment, microbial contamination, and solar radiation) or to ground-based models of spaceflight will alter human immune responses, but specific antibody responses have not been fully evaluated. OBJECTIVE: We sought to determine whether exposure to the 8-month Antarctic winter-over model of spaceflight would alter human antibody responses. METHODS: During the 1999 Australian National Antarctic Research Expeditions, 11 adult study subjects at Casey, Antarctica, and 7 control subjects at Macquarie Island, sub-Antarctica, received primary and secondary immunizations with the T cell-dependent neoantigen bacteriophage phi X-174. Periodic plasma samples were analyzed for specific antibody function. RESULTS: All of the subjects from Casey, Antarctica, cleared bacteriophage phi X-174 normally by 1 week after primary immunization, and all had normal primary and secondary antibody responses, including immunologic memory amplification and switch from IgM to IgG antibody production. One subject showed a high normal pattern, and one subject had a low normal pattern. The control subjects from Macquarie Island also had normal immune responses to bacteriophage phi X-174. CONCLUSIONS: These data do not support the hypothesis that de novo specific antibody responses of subjects become defective during the conditions of the Antarctic winter-over. Because the Antarctic winter-over model of spaceflight lacks the important factors of microgravity and solar radiation, caution must be used in interpreting these data to anticipate normal antibody responses in long-term spaceflight.

Implantable cardioverter defibrillator electrogram recognition with a multilayer perceptron.

With the continuing development of new pacing and shock modalities, implantable cardioverter defibrillators must be able to recognize an increasingly wider range of arrhythmias so that therapy is delivered in an optimal way. Current rate-based systems can no longer meet this need. It is, therefore, necessary to develop new techniques that consider waveform morphology in addition to heart rate. Any developments, however, must be compatible with the strict power and space constraints imposed by implantable devices. Artificial neural networks offer a potentially viable way of meeting these objectives. In this article an artificial neural network based approach to the classification of arrhythmias from the ventricular intracardiac electrogram is described. It performs its classification on a set of easily extracted features that characterize waveform morphology and heart rate. Simulations showed that the artificial neural network performed better than a rate-based scheme similar to those used in some commercial devices.

Optical design in a flow system for imaging cells.

The imaging flow cytometer is an instrument that acquires the images of cells in a flow system. These images are analyzed for real-time cell classification and sorting. The optical units in the system perform the functions of laser beam focusing, cell detection, and cell imaging. The glass nozzle in which the cell stream flows introduces air-glass optical interfaces, resulting in optical aberrations that impair performance. This report describes the analysis of the optical aberrations in nozzles fabricated from a cylindrical glass capillary tube. Flat surfaces could be machined on the originally cylindrical surface to reduce the severity of these aberrations. The analysis shows that a nozzle with three flat surfaces is a feasible low-cost solution.

Interval-coded texture features for artifact rejection in automated cervical cytology.

In order to improve the separation between abnormal cells and noncellular artifacts in the CERVIFIP automated cervical cytology prescreening system, 22 different object texture features were investigated. The features were all statistical parameters of the pixel density histograms or one-dimensional filtered values of central and border regions of the object images. The features were calculated for 231 images (100 cells and 131 artifacts) detected as Suspect Cells by the current CERVIFIP and were then tested in hierarchical and linear discriminant classifiers. After selecting the two best features for use in a hierarchical classifier, 83% correct classification was achieved. One of these features was specifically designed to remove poorly focused objects. With maximum likelihood discrimination using all 22 features, an overall correct classification rate of 90% was obtained.

Development of an imaging flow cytometer.

A cell analyzer that combines the characteristics of image cytometry and flow cytometry is being designed and constructed at the University of Sydney. This paper describes the image acquisition and processing components and some preliminary applications. Cells stained by a fluorescent dye and suspended in a liquid medium are conveyed by a hydraulic system to a flow channel assembly, where they are detected and illuminated by a laser beam. A two-dimensional charge-coupled device is used to acquire the cell images. Image processing and classification is to be carried out by a special-purpose computer comprising an array of four conventional microprocessors and a highly parallel processor consisting of an array of 32 X 32 processing elements. The analyzer will be capable of using morphologic, immunologic and biochemical information to classify and sort up to 500 cells per second. Because of its unique characteristics, the instrument will be of particular use in tumor heterogeneity studies.

Multicompartment models of cancer chemotherapy incorporating resistant cell populations.

The pharmacokinetics of antineoplastic drugs based on compartmental models are combined with deterministic exponential growth models of tumors containing drug-resistant and sensitive cells. Model predictions for single-drug therapy are compared with in vivo data obtained by other investigators for L1210 t-cell leukemia in mice treated with BCNU and Ara-C and for in vitro treatment of L1210 with Ara-C. The model and data compare favorably in terms of rate of tumor growth and duration of drug action for both constant infusion and bolus delivery of the drugs.

Non-invasive technique for examining the respiratory proprioceptor system in man.

Our technique enables non-invasive experiments to be conducted on the proprioceptor part of respiratory control, while eliminating misleading responses due to interaction with the chemoreceptor system; interaction was prevented by stabilizing arterial PO2 and PCO2 with the aid of an optimal regulator based on a mini-computer which controlled the inspired gas mixture. The proprioceptor system in a human was disturbed by applying positive pressure pulses at the mouth, responses were derived from continuous air-flow measurement. The classical inflation inhibiting reflex and an effect akin to Head's paradoxical reflex were demonstrated.

Technique for assessing the response of the respiratory controller to hypoxia and hypercapnia.

A technique, suitable for clinical practice, has been developed to measure quantitatively and separately the effects of hypercapnia on the central and peripheral chemoreceptors, and hypoxia on the peripheral chemoreceptors of a human subject. The technique uses a model to account for the dynamics of CO2 transport in the brain and is based on current concepts of the chemoreceptor system and makes a minimum of assumptions. The method was tested in one subject and there was evidence for hysteresis in the response to hypoxia and short-term adaptation in the response to hypercapnia of the chemoreceptor controller.

Instability of the carbon dioxide stimulus under the "mixed venous isocapnic" conditions advocated for testing the ventilatory response to hypoxia.

Meaningful and reproducible ventilatory responses to hypoxia cannot be obtained from the mixed venous isocapnic test reported by Rebuck and Campbell if it is not recognized that the CO2 drive increases progressively for at least 6 to 10 min after the PCO2 step.