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Biomedical subjects

J Riess

Publications and source records attributed to J Riess.

At least 19 recordsLinked to original sources
PubMed2000

Adaptive neural network control of cyclic movements using functional neuromuscular stimulation.

In this study, we evaluated the performance of an adaptive feedforward controller and its ability to automatically develop and customize stimulation patterns for use in functional neuromuscular stimulation (FNS) systems. Results from previous experiments using the pattern generator/pattern shaper (PG/PS) controller to generate isometric contractions demonstrated its ability to adjust stimulation patterns to account for recruitment nonlinearities and muscle dynamics. In this study, the PG/PS controller was tested under isotonic conditions. This evaluation required the PG/PS controller to account for muscle length-tension and force-velocity properties as well as limb dynamics. The performance of the adaptive controller was also compared with that of a proportional-derivative (PD) feedback controller. The PG/PS controller is composed of a neural network system that adaptively filters a periodic signal to produce a muscle stimulation pattern for generating cyclic movements. We used computer-simulated models to determine controller parameters for the PG/PS and PD controller that perform well across a variety of musculoskeletal systems. The controllers were then experimentally evaluated on both legs of two subjects with spinal cord injury. Results indicated that the PG/PS controller was able to achieve and maintain better tracking performance than the PD controller. This study indicates that the PG/PS control system may provide an effective mechanism for automatically customizing stimulation patterns for individuals using FNS systems.

Algorithms↗
PubMed1997

Evaluation of FNS control systems: software development and sensor characterization.

Functional Neuromuscular Stimulation (FNS) systems activate paralyzed limbs by electrically stimulating motor neurons. These systems have been used to restore functions such as standing and stepping in people with thoracic level spinal cord injury. Research in our laboratory is directed at the design and evaluation of the control algorithms for generating posture and movement. This paper describes software developed for implementing FNS control systems and the characterization of a sensor system used to implement and evaluate controllers in the laboratory. In order to assess FNS control algorithms, we have developed a versatile software package using Lab VIEW (National Instruments, Corp). This package provides the ability to interface with sensor systems via serial port or A/D board, implement data processing and real-time control algorithms, and interface with neuromuscular stimulation devices. In our laboratory, we use the Flock of Birds (Ascension Technology Corp.) motion tracking sensor system to monitor limb segment position and orientation (6 degrees of freedom). Errors in the sensor system have been characterized and nonlinear polynomial models have been developed to account for these errors. With this compensation, the error in the distance measurement is reduced by 90 % so that the maximum error is less than 1 cm.

Computer Systems↗
PubMed1996

Aerobic preservation of organs using a new perflubron/lecithin emulsion stabilized by molecular dowels.

The purpose of the study reported here was to explore a new strategy for the aerobic preservation of transplants using stable concentrated fluorocarbon emulsions as an oxygen delivery system. Fluorocarbons (FCs) are synthetic molecules, chemically and biologically inert, with a high oxygen-dissolving capacity. As they do not mix with water, it is necessary to emulsify them for intra-vascular use. Perfluorooctyl bromide (or perflubron) can be emulsifled with egg-yolk phospholipid (EYP), a nontoxic emulsifiant. The recent adjunction of amphiphilic fluorocarbon-hydrocarbon diblock molecules allows the obtaining of stable emulsions. By contrast with hemoglobin, fluorocarbons release oxygen following Henry's linear law rather than Barcroft's sigmoid curve. Release of oxygen by the FCs is only slightly influenced by temperature, which is an advantage for the preservation of organs. We tested a new 90% w/v fluorocarbon stem emulsion (perflubron/EYL/F6H10) diluted to 36% w/v with a hydroelectrolytic solution containing albumin, on four multiple organ blocks (MOBs; heart-lungs, liver, pancreas, kidneys, small intestine) of rats (EMOBs). Five control MOBs were perfused with a 50% v/v mixture of rat-blood and Krebs solution (KBMOBs). The lungs were ventilated with a FiO2 = 100%. In all cases the survival of the MOBs was greater than 210 min, with stable hemodynamics and preserved hydroelectrolytic and acid-base balances. The levels of lactate, amylase, and CK of the EMOBs were inferior (P < 0.05) to those of the KBMOBs between the first and the second hour. The diuresis of the EMOBs was higher (P < 0.05) than that of the KBMOBs (5.65 +/- 1.76 vs 1.21 +/- 0.28 mg/min). The production of bile, and the AST and ALT levels, were not significantly different. The PaO2 of the EMOBs was higher (P < 0.01) than for the KBMOBs. In normothermy, the maintenance of an aerobic metabolism using the FC emulsion caused less damage to the organs. Aerobic preservation of organs using FC emulsions therefore appears to be an attractive alternative to the presently used cold ischemia.

Animals↗
PubMed1991

Influence of the 100% w/v perfluorooctyl bromide (PFOB) emulsion dose on tumour radiosensitivity.

The radiosensitizing effect of a 100% w/v emulsion of a fluorocarbon, PFOB, which carries 4 times more oxygen than does Fluosol-DA 20% emulsion, was studied on two human tumour xenografts (HRT18 and HT29) and the murine tumour EMT6. This effect was compared with that obtained with carbogen alone. The fluorocrit (amount of fluorocarbon in the blood) and haematocrit remained unchanged from 7 to 65 min post-injection of the emulsion (8 ml/kg). Tumour-bearing mice were pretreated with 100% w/v PFOB emulsion doses ranging from 2 to 15 ml/kg in the presence of carbogen for 30 min prior to and during irradiation. The fluorocrit increased from 1.5% to 9.5% as the dose of 100% w/v PFOB emulsion increased from 2 to 15 ml/kg. The haematocrit remained the same for all the fluorocarbon emulsion doses used. Tumour radiosensitization varied with the fluorocarbon emulsion dose. Clinically relevant doses (2-4 ml/kg) of the 100% w/v PFOB emulsion plus carbogen produced significantly more radiosensitization than carbogen alone, with sensitizing enhancement ratios of 1.4 for EMT6 and 1.7 for HRT18. The radiosensitivity of HRT18 cells was thus very close to that obtained with normally oxygenated cells. For higher doses (8-15 ml/kg) the radiosensitizing effect of 100% w/v PFOB emulsion plus carbogen becomes comparable to that of carbogen alone. These experiments show that clinically useful doses of 100% w/v PFOB plus carbogen produced tumour radiosensitization only at relatively low fluorocrits. Thus the fluorocrit, and hence the fluorocarbon's oxygen-carrying capacity, is not the only factor involved in radiosensitizing tumour cells by oxygen-carrying fluorocarbon emulsions.

Adenocarcinoma↗
PubMed1989

New high O2 carrying perfluorochemical emulsions: toxicity, radiosensitivity of GM-CFC and development of metastases in mice.

The effects of two new concentrated perfluorochemical emulsions based on F-66E and PFOB, which carry significantly more oxygen than Fluosol-DA 20%, were tested on normal tissues (toxicity and radiation response) and on the development of metastases from Lewis Lung Carcinoma (3LL) in female C57 BL/6 mice. Twenty one days after injection of F-66E or PFOB emulsions (15 ml/kg body weight), the spleen and liver weights were significantly increased but had returned to normal after 2-3 months. Splenomegaly already observed in 3LL bearing mice was significantly increased by F-66E emulsion injection. The radiosensitivity of GM-CFC was not altered when unanesthetized GM-CFC was not altered when unanesthetized mice were pretreated with F-66E emulsions and/or carbogen 1 hr prior to and during irradiation. The rate of tumor take and the period before detection of tumors were not modified when an emulsion of F-66E was injected simultaneously or 10 days after 3LL cells. Mean survival of mice, and the number of metastases on lung surfaces were similar in F-66E injected mice and control mice.

Animals↗