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Biomedical subjects

R J Jaeger

Publications and source records attributed to R J Jaeger.

At least 37 records · Page 2Linked to original sources
PubMed1987

Characterization and control of muscle response to electrical stimulation.

The maintenance of upright posture in neurologically intact human subjects is mediated by two major nervous pathways. The first, leading from the cerebral cortex through the spinal cord to motor neurons, activates muscles which produce postural movements. The second, leading from various sensory organs to higher centers, provides sensory feedback regarding the postural state. The path through the spinal cord is no longer intact in victims of spinal cord injury and loss of normal control of muscle activity results. Functional neuromuscular stimulation (FNS) has been shown as a feasible method for obtaining muscle contraction in paraplegics and has been proposed as a means for control of antero-posterior sway to make upright posture possible for these individuals. Before muscle can be controlled through the use of FNS, the response of muscle to electrical stimulation must be understood. In past studies, linear control theory has been applied to the analysis of this response and to the testing of various controllers. The aim of this study was to demonstrate some control issues in FNS using linear control theory, as it applies to electrical stimulation of muscle for stabilization of posture. The linearity of the muscle response was improved through closed-loop control using pole compensation techniques. The excess phase shift of the system due to the time delay in the muscle response, however, limits the ability to increase the open-loop gain in order to obtain improved performance. A suggestion for further study is the application of this methodology for uses in posture control.

Electric Stimulation↗
PubMed1986

Standing performance of persons with paraplegia.

This study measures standing stability of four individuals with paraplegia using knee-ankle-foot orthoses (KAFOs) with a center-of-force monitoring platform as compared with similar data from 10 neurologically healthy subjects. Both groups were compared under conditions of quiet standing with eyes open and closed and with hands on and off parallel bars. Individuals with paraplegia were also tested under similar conditions with the ankles of their KAFOs mechanically unlocked and with bilateral functional neuromuscular stimulation of the quadriceps muscles. Sway path, mean amplitude, and mean frequency were measured for each subject. We found that postural stability in paraplegic individuals using KAFOs compared favorably with the control group under conditions of eyes open and closed with hands on parallel bars; however, visual information was much more important for paraplegic individuals during quiet stance. Unlocking the ankles of the KAFOs resulted in an increase in swap path and mean frequency. Functional muscular stimulation of the quadriceps muscles resulted in standing stability slightly less than with KAFOs. Although KAFOs may not be the ideal assistive device for various reasons, postural stability appears reasonable, and other proposed orthoses must be comparable in order to be considered as an alternative.

Adult↗
PubMed1986

Design and simulation of closed-loop electrical stimulation orthoses for restoration of quiet standing in paraplegia.

Simulation models of quiet standing have been developed to study the potential use of closed-loop stimulation orthoses in mid-thoracic spinal cord injury. The first model (static) consists of a multi-link inverted pendulum. The second model (dynamic) consists of a single-link inverted pendulum, with electrically stimulated muscles providing balancing activation at the ankle joint and stabilization of the knee and hip joints. The initial simulations have shown that it may be possible to restore quiet standing in paraplegic individuals within certain limits subject to biomechanical constraints and to the available torque produced by the stimulated muscle.

Computer Simulation↗
PubMed1986

Hazards to health from environmental lead exposure: a review of recent literature.

There are adequate demonstrations of the adult and pediatric health risks associated with lead exposure. This document presents the scientific facts surrounding human health effects as well as providing an interpretation of some of the animal toxicology studies. There are numerous circumstances where economic and societal pressures have resulted in the continued use of materials that are potentially toxic, hazardous and injurious to the public health and welfare. While declining, the present use of lead in gasoline and its airborne release from smelting and metal refining industries located near metropolitan centers is no exception. The demonstration that continued lead exposure from airborne sources results in intellectual deficiency should be sufficient to result in the mobilization of public health resources and the minimization or elimination, if necessary, of such hazards to the public welfare. Based on this review, this is the position that is suggested by the authors of this document.

Absorption↗
PubMed1986

Health risk analysis of human exposures to soil amended with sewage sludge contaminated with polychlorinated dibenzodioxins and dibenzofurans.

The risk of cancer to humans exposed to soil treated with wastewater/sewage treatment plant sludge, known to be contaminated with small amounts of polychlorinated dibenzodioxins and dibenzofurans (PCDDs and PCDFs), was evaluated. The particulate-bound PCDDs and PCDFs are found in trace amounts in the effluent from ground water pumping (dewatering) at an abandoned wood preservation facility. The water, which was sent to a water recovery plant, underwent primary and secondary treatment prior to discharge. The residual sludge was added to agricultural soil as a conditioner. The present analysis treats the extreme case of sludge applied near the home of a target individual, a lifetime resident, who is also a farm worker in the area of the application. The successive stages of infancy, childhood and adulthood are treated separately to assess the contributions of typical age-specific indoor and outdoor activities on exposure rates. Five toxicity rating schemes using so-called TCDD equivalents, and two unit risk slopes are applied to the chemical profile in sludge to determine the cancer potency of the soil contaminants. These risk estimates range from 1 X 10-8 to 3 X 10-7.

Adult↗
PubMed1984

Muscle spindle contributions to the stretch-evoked electromyogram: nerve block studies.

Application of external torque to cause joint rotation evokes electromyogram (EMG) activity in the stretched muscles. These responses were studied in the tibialis anterior (TA) and flexor carpi ulnaris (FCU) muscles of normal human subjects in conjunction with a nerve block procedure by a local anesthetic agent. In both muscles, differences were observed between the myotatic and postmyotatic portions of the evoked EMG response. During recovery from a complete nerve block, the late components of the EMG (postmyotatic and stabilizing responses) recovered to the preblock magnitude faster than the early components (myotatic and late myotatic responses). Following partial nerve block, the late EMG components were diminished to a lesser extent and recovered faster than the early EMG components. This study suggests that peripheral afferent inputs are obligatory for the myotatic and late myotatic EMG responses. The effects of peripheral afferent inputs on postmyotatic responses are to modulate these later responses. However, the absence of peripheral afferent inputs will not prevent or even delay postmyotatic responses.

Adult↗
PubMed1984

Lower extremity functional neuromuscular stimulation in cases of spinal cord injury.

Functional neuromuscular stimulation (FNS) provides a mechanism for the activation of muscles paralyzed by injury to the spinal cord. Although this technique was first used to treat patients with spinal cord injury over 20 years ago, only recent advances in electronics and biomechanics have made it a promising aid for the rehabilitation of these patients. Thus far, restoration of palmar prehension and lateral prehension in quadriplegics and of standing and biped gait in paraplegics has been achieved under carefully controlled laboratory conditions. This article reviews the current status of FNS and its potential as a practical tool to aid spinal cord-injured patients. Neurosurgeons who care for these patients might be expected to be involved in the future use of FNS if implantable systems are developed and tested.

Biofeedback, Psychology↗
PubMed1984

Effects of acrylonitrile on tissue glutathione concentrations in rat, mouse, and hamster.

Glutathione (GSH) is implicated in acrylonitrile (ACN) detoxification. To add to the understanding of ACN detoxification we studied the effects of ACN on GSH levels in various tissues and species. GSH in four tissues (brain, lung, liver, and kidney) from three species (rat, mouse and hamster) were assessed at five time points subsequent to ACN treatment. ACN-induced decreases in GSH were most pronounced in the rat and occurred in all four tissues and were less pronounced in mouse and hamster tissues. Liver GSH was most effected in all species.

Acrylonitrile↗
PubMed1983

Repeated pulmonary function evaluation following bleomycin treatment.

A computerized, nonsurgical, pulmonary function measurement method was tested for sensitivity and utility in detecting the development of fibrosis. Bleomycin, a fibrogenic agent, was intratracheally instilled into male Fisher 344 rats. Respiratory function was monitored in restrained, awake animals before treatment and for the subsequent 4 wk. In the first week, among responders, a significant (p less than 0.05) drop in body weight, tidal volume, and compliance was accompanied by a significant increase in respiratory frequency. Minute volume increased in the second week. Although body weight, tidal volume, and compliance returned to baseline values in the following weeks, respiratory frequency and minute volume remained significantly elevated. With the methods used here, respiratory rate change was the parameter most sensitive to the effects of bleomycin in vivo.

Animals↗
PubMed1983

Response to sudden torques about ankle in man: V effects of peripheral ischemia.

Sudden dorsiflexions and plantar flexions of the foot were imposed by a torque motor while blood flow to the lower leg was occluded by a sphygmomanometer cuff. Seated subjects were instructed to resist the torques and restore the foot to its original position as rapidly as possible. Measurements of the first two electromyographic (EMG) responses were made in the soleus (SOL) and anterior tibial (TA) muscles. These are the myotatic reflex at about 40 ms and the postmyotatic response at about 120 ms. In the anterior tibial muscle, the myotatic component often occurs at 60- to 90-ms latency and is continuous with the postmyotatic component. After about 20 min of ischemia, there is a rapid and eventually complete loss of the myotatic component of the response in the stretched muscle. Concurrent with the loss of the myotatic reflex there is usually a reduction of the postmyotatic component. The latency of postmyotatic component remains unchanged, even after the myotatic reflex is abolished. Voluntary restoration of the foot to its original position in opposition to the motor torque is delayed and slowed by the time that the myotatic reflex has vanished. By measuring electromyographic responses to visually triggered reactions, we demonstrate that the reduction of the postmyotatic response is not due to failure of the efferent pathway. On this basis we discuss the possible contributions made by myotatic mechanisms to the tasks of load compensation and maintenance of muscle tone. Hoffmann reflexes were evoked in similar experiments with stimulation of the posterior tibial nerve at the popliteal fossa, distal to the cuff. The maximal direct motor response and muscle twitch are unaffected by loss of the H-reflex. Myotatic and Hoffmann reflexes were both evoked with torque perturbations and with a stimulating electrode proximal to a below-the-knee cuff. In this case, the myotatic reflex failed while the maximal H-reflex was slightly facilitated. The loss of the myotatic reflex was accompanied by a modest reduction in the direct motor response to electrical stimulation and a somewhat greater reduction in the postmyotatic response to torque perturbation. The data are interpreted to support a dual role for the primary afferent pathway in the control of voluntary movements. It provides the fastest path for the activation of a stretched muscle to initiate a load-compensating contraction. It also provides a form of servo assistance in modulating descending control signals. The degree of this assistance is estimated. In this simple experimental paradigm, functional contributions of the reflex arc are demonstrated.

Ankle Joint↗
PubMed1983

Induced tolerance to acrylonitrile toxicity by prior acrylonitrile exposure.

Pretreatment by inhalation with sublethal concentrations of acrylonitrile protects rats from subsequent, normally lethal, ACN exposures. However, inhalation-induced tolerance to ACN does not protect against subsequent poisoning by cyanide. Metabolic liberation of cyanide has been suggested to be responsible for the toxicity of ACN. Protection against ACN toxicity is not provided by pretreatment with compounds which have structural similarity to ACN, i.e. acrylamide or ethylene, nor by cyanide per se. Enzyme induction with Aroclor 1254 also does not protect against ACN toxicity. The latter data suggest that the tolerance resulting from ACN pretreatment is not the result of enzyme induction and the basis for the protective effect of ACN inhalation pretreatment remains unclear.

Acrylonitrile↗
PubMed1982

Respiratory and metabolic response of rats and mice to formalin vapor.

The irritant effect of repeated inhalation exposure to vapors of aqueous formalin (formaldehyde concentration, 15 ppm) in male Charles River CD rats and male C57BL6/F1 mice was determined. The data suggest that rats are relatively insensitive to this irritant while mice are substantially more sensitive, the latter showing a comparable reduction in tidal volume, but a greater decrease in respiratory rate and, as a consequence, minute volume. CO2 production, a reflection of total metabolism, as well as body temperature, were decreased to a greater extent in mice than in rats. The decreased minute ventilation and associated decrease in temperature, responses occurring to a greater extent in the mouse, may decrease both the net formaldehyde dose as well as the toxic actions of formaldehyde that are dependent on systemic metabolic activity.

Animals↗
PubMed1982

Thermal decomposition products of PVC plastics: effects on guinea pig lung mechanics and pulmonary mixed function oxidase activity.

The toxicity of the thermal decomposition products of polyvinyl chloride (PVC) plastic were studied and their pulmonary effects in guinea pigs evaluated. Measures of toxicity included lethality, alteration in lung mechanical function, lung mixed function oxidase enzyme activity and lung organ to body weight ratio. A technical PVC formulation (composition not known) was more lethal than another formulation designed to simulate electrical insulation. Both materials and pure PVC produced highly irritant gases as measured by changes in respiratory rate and compliance (decreased) and total flow resistance (increased). While adverse pulmonary mechanical effects in lung function were observed, lung biochemical parameters were relatively unchanged.

Animals↗
PubMed1982

Myoelectric responses at flexors and extensors of human wrist to step torque perturbations.

1. Torque-step perturbations were applied to flex or extend the wrists of normal human subjects. The electromyographic activity (EMG) of two of the stretched muscles, flexor carpi radialis and extensor carpi radialis, was monitored. 2. Based on functional characteristics and temporal bursting patterns, the EMG responses were partitioned into four distinct temporal intervals : 30-60, 60-120, 120-200, and greater than 200 ms after the onset of the torque step. The last interval continues for the duration of the step input: 200- 400 ms was chosen to represent activity in this interval. 3. EMG responses in the first two intervals show short, stable latencies and amplitudes that depend on the level of muscle contraction prior to the torque step. They are facilitated by any instruction requiring a reaction by the subject. They are reflexes that cannot be voluntarily suppressed by instruction to the subject. 4. The third EMG response is a triggered response. It is not a reflex because its appearance or absence is absolutely under voluntary control. Unlike true voluntary responses, there exists no dichotomy in responses latency or variability between known versus unknown directions of torque steps. 5. We consider that a truly voluntary response to a torque perturbation does not begin until about 200 ms after the step, which is on the order of visual or auditory reaction times. 6. The EMG responses were similar in both the wrist flexor and extensor studied. Ankle flexors and extensors do not show such similarity. 7. The EMG responses at the wrist and ankle are compared and shown to have many similarities. A general scheme for their classification is discussed.

Adult↗
PubMed1982

Afferent contributions to stretch-evoked myoelectric responses.

1. Step torque perturbations were applied to flex or extend the wrists of normal human subjects who were instructed to restore the joint to its initial position as quickly as possible. The resulting electromyographic (EMG) activity was recorded from the flexor carpi radialis, flexor carpi ulnaris, and extensor carpi radialis. Experiments were performed under control and three altered conditions of the limb: 1) ischemia, 2) vibration, and 3) local ulnar nerve anesthesia. The effects of the procedures on the EMG responses in four poststimulus intervals--the myotatic (30-60 ms), late myotatic (60-120 ms), postmyotatic (120-200 ms), and stabilizing (200-400 ms)--were studied. 2. Ischemia was induced in the forearm by means of a sphygmomanometer cuff inflated to 150 mm of mercury around the upper arm. After about 20 min of ischemia the stretch-evoked EMG activity over the 30-60-ms and 60-120-ms intervals were abolished, while the longer latency responses persisted. 3. Vibration at frequencies between 50 and 120 Hz was applied to the tendon of the stretched muscle. Vibration consistently reduced the EMG activity only in the 30-60-ms interval. 4. The ulnar nerve was blocked near the elbow joint by local anesthetic. Varying degrees of block were obtained, from a mild sensory impairment to a complete block. At intermediate degrees of block, EMG activity in the 30-60-ms and 60-120-ms intervals were attenuated with little alteration in later responses. 5. The data are used to differentiate functionally the myoelectric responses evoked in four poststimulus time segments in the stretched muscle by step torque perturbations.

Adult↗
PubMed1982

Effect of hypoxia on the acute toxicity of acrylonitrile.

The modifying effects of hypoxia (7% 02) on acute lethality; and concentration of tissues non-protein sulfhydryls (NPSH) after acrylonitrile (ACN) exposure were studied. Hypoxia plus ACN exposure in male rats produced a substantial increase in mortality and a greater decrease in NPSH than ACN or hypoxia alone. NPSH in blood did not decrease significantly as a result of hypoxia, ACN or the combination.

Acrylonitrile↗