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Biomedical subjects

G L Gottlieb

Publications and source records attributed to G L Gottlieb.

At least 19 recordsLinked to original sources
PubMed1992

Basic functions of variability of simple pre-planned movements.

A model of a pre-planned single joint movements performed without feedback is considered. Modifications of this movement result from transformation of a trajectory pattern f(t) in space and time. The control system adjusts the movement to concrete external conditions specifying values of the transform parameters before the movement performance. The pre-planned movement is considered to be simple one, if the transform can be approximated by an affine transform of the movement space and time. In this case, the trajectory of the movement is x(t) = Af (t/tau + s) + p, were A and l/tau are space and time scales, s and p are translations. The variability of movements is described by time profiles of variances and covariances of the trajectory x(t), velocity v(t), and acceleration a(t). It is assumed that the variability is defined only by parameters variations. From this assumption follows the main finding of this work: the variability time profiles can be expanded on a special system of basic functions corresponding to established movement parameters. Particularly, basic functions of variance time profiles, reflecting spatial and temporal scaling, are x2(t) and t2v2(t) for trajectory, v2(t) and (v(t)+t.a(t))2 for velocity, and a2(t) and (2a(t)+t.j(t))2, where j(t) = d3x(t)/dt3, for acceleration. The variability of a model of a reaching movement was studied analytically. The model predicts certain peculiarities of the form of time profiles (e.g., the variance time profile of velocity is bi-modal, the one of acceleration is tri-modal, etc.). Experimental measurements confirmed predictions. Their consistence allows them to be considered invariant properties of reaching movement. A conclusion can be made, that reaching movement belongs to the type of simple pre-planned movements. For a more complex movement, time profiles of variability are also measured and explained by the model of movements of this type. Thus, a movement can be attributed to the type of simple pre-planned ones by testing its variability.

Elbow Joint↗
PubMed1992

Virtual trajectories of single-joint movements performed under two basic strategies.

The framework of the equilibrium point hypothesis has been used to analyse motor control processes for single-joint movements. Virtual trajectories and joint stiffness were reconstructed for different movement speeds and distances when subjects were instructed either to move "as fast as possible" or to intentionally vary movement speed. These instructions are assumed to be associated with similar or different rates of change of hypothetical central control variables (corresponding to the speed-sensitive and speed-insensitive strategies). The subjects were trained to perform relatively slow, moderately fast and very fast (nominal movement times 800, 400 and 250 ms) single-joint elbow flexion movements against a constant extending torque bias. They were instructed to reproduce the motor command for a series of movements while ignoring possible changes in the external torque which could slowly and unpredictably increase, decrease, or remain constant. The total muscle torque was calculated as a sum of external and inertial components. Fast movements over different distances were made with the speed-insensitive strategy. They were characterized by an increase in joint stiffness near the midpoint of the movements which was relatively independent of movement amplitude. Their virtual trajectories had a non-monotonic N-shape. All three arms of the N-shape scaled with movement amplitude. Movements over one distance at different speeds were made with a speed-sensitive strategy. They demonstrated different patterns of virtual trajectories and joint stiffness that depended on movement speed. The N-shape became less apparent for moderately fast movements and virtually disappeared for the slow movements. Slow movements showed no visible increase in joint stiffness.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Functional status outcomes of a nursing intervention in hospitalized elderly.

This paper examines the effectiveness of a nursing intervention for elderly hospitalized patients (N = 235) as measured by functional outcomes. A nursing intervention targeted at factors which influence acute confusion or delirium employed strategies to educate nursing staff, mobilize patients, monitor medication and make environmental and sensory modifications. Subjects who received the intervention were more likely to improve in functional status from admission to discharge than subjects who did not receive the intervention.

Activities of Daily Living↗
PubMed1992

Organizing principles for single joint movements: V. Agonist-antagonist interactions.

1. Normal human subjects made discrete elbow flexions in the horizontal plane under different task conditions of initial or final position, inertial loading, or instruction about speed. We measured joint angle, acceleration, and electromyographic signals (EMGs) from two agonist and two antagonist muscles. 2. For many of the experimental tasks, the latency of the antagonist EMG burst was strongly correlated with parameters of the first agonist EMG burst defined by a single equation, expressed in terms of the agonist's hypothetical excitation pulse. Latency is proportional to the ratio of pulse duration to pulse intensity, making it proportional to movement distance and inertial load and inversely proportional to planned movement speed. However, these rules are not sufficient to define the timing of every possible single joint movement. 3. For movements described by the speed-insensitive strategy, the quantity of both antagonist and agonist muscle activity can be uniformly associated with selected kinetic measures that incorporate muscle force-velocity relations. 4. For movements collectively described by the speed-sensitive strategy, (i.e., that have direct or indirect constraints on speed), no single rule can describe all the combinations of agonist-antagonist coordination that are used to perform these diverse tasks. 5. Estimates of joint viscosity were made by calculating the amount of velocity-dependent torque used to terminate movements on target. These estimates are similar to those that have previously been made of limb viscosity during postural maintenance. They imply that a significant component of muscle activity must be used to overcome these forces. 6. These and previous results are all consistent with a dual-strategy hypothesis for those single-joint movements that are sufficiently fast to require pulse-like muscle activation patterns. The major features of such patterns (pulse intensities, durations, and latencies) are determined by central commands programmed in advance of movement initiation. The selection between speed-insensitive or speed-sensitive rules of motoneuron pool excitation is implicitly specified by the nature of speed constraints of the movement task.

Electromyography↗
PubMed1991

Gender differences in age effect on brain atrophy measured by magnetic resonance imaging.

A prospective sample of 69 healthy adults, age range 18-80 years, was studied with magnetic resonance imaging scans (T2 weighted, 5 mm thick) of the entire cranium. Volumes were obtained by a segmentation algorithm that uses proton density and T2 pixel values to correct field inhomogeneities ("shading"). Average (+/- SD) brain volume, excluding cerebellum, was 1090.91 ml (+/- 114.30; range, 822.19-1363.66), and cerebrospinal fluid (CSF) volume was 127.91 ml (+/- 57.62; range, 34.00-297.02). Brain volume was higher (by 5 ml) in the right hemisphere (P less than 0.0001). Men (n = 34) had 91 ml higher brain and 20 ml higher CSF volume than women (n = 35). Age was negatively correlated with brain volume [r(67) = -0.32, P less than 0.01] and positively correlated with CSF volume (r = 0.74, P less than 0.0001). The slope of the regression line with age for CSF was steeper for men than women (P = 0.03). This difference in slopes was significant for sulcal (P less than 0.0001), but not ventricular, CSF. The greatest amount of atrophy in elderly men was in the left hemisphere, whereas in women age effects were symmetric. The findings may point to neuroanatomic substrates of hemispheric specialization and gender differences in age-related changes in brain function. They suggest that women are less vulnerable to age-related changes in mental abilities, whereas men are particularly susceptible to aging effects on left hemispheric functions.

Adult↗
PubMed1991

Relativistic effects in single-joint voluntary movements.

We assume that there is an upper limit for the rate of change of controlled variables in the motor control system. Superposition of two single-joint motor programs can lead to a distortion of their simple algebraic summation similar to relativistic Lorenz transformations. Experiments were carried out with the subjects performing fast oscillatory elbow movements on the background of a smooth elbow flexion. Changes in the period of oscillations during the smooth movement were used as index of time transformations. Statistically 5%-7% changes in the period were observed for each of the subjects corresponding to the predictions of the model.

Humans↗
PubMed1991

Reconstruction of shifting elbow joint compliant characteristics during fast and slow movements.

The purpose of this study was to experimentally investigate the applicability of the equilibrium-point hypothesis to the dynamics of single-joint movements. Subjects were trained to perform relatively slow (movement time 600-1000 ms) or fast (movement time 200-300 ms) single-joint elbow flexion movements against a constant extending torque bias. They were instructed to reproduce the same time pattern of central motor command for a series of movements when the external torque could slowly and unpredictably increase, decrease, or remain constant. For fast movements, the total muscle torque was calculated as a sum of external and inertial components. Analysis of the data allowed reconstruction of the elbow joint compliant characteristics at different times during execution of the learned motor command. "Virtual" trajectories of the movements, representing time-varying changes in a central control parameter, were reconstructed and compared with the "actual" trajectories. For slow movements, the actual trajectories lagged behind the virtual ones. There were no consistent changes in the joint stiffness during slow movements. Similar analysis of experiments without voluntary movements demonstrated a lack of changes in the central parameters, supporting the assumption that the subjects were able to keep the same central motor command in spite of externally imposed unexpected torque perturbations. For the fast movements, the virtual trajectories were N-shaped, and the joint stiffness demonstrated a considerable increase near the middle of the movement. These findings contradict an hypothesis of monotonic joint compliant characteristic translation at a nearly constant rate during such movements.

Adult↗
PubMed1991

Delirium in the medically ill elderly: operationalizing the DSM-III criteria.

This prospective study determined the incidence and prevalence of delirium in 235 consecutive subjects over age 70 admitted to a general medicine hospital service. The DSM-III criteria for delirium were operationalized. Using accepted screening procedures, patients were referred for evaluation by a psychiatrist who determined whether delirium was present by applying explicit operational definitions to each of the DSM-III criteria. Data on presence and severity of each of the DSM-III symptoms were recorded. Analysis of these data indicates that the DSM-III criteria describe a discrete, recognizable syndrome. However, some of the symptoms are more specific than others in identifying the syndrome in this population.

Aged↗
PubMed1990

Sleep disorders and their management. Special considerations in the elderly.

Complaints of insomnia and disordered sleep are pervasive among the elderly, and reduced total sleep time and changes in sleep architecture are considered to be normal in the aging process. Additionally, numerous medical and psychiatric disorders that are highly prevalent in the geriatric population are known to affect sleep adversely. Epidemiologic data indicate that at least 5 million older adults suffer severe disorders of sleep and that most people with severe insomnia receive no treatment for this troubling symptom. However, although the elderly comprise only about 12 percent of the American population, between 35 and 40 percent of all prescriptions for sedative hypnotics are written for people over the age of 60. Moreover, approximately 23 percent of Americans over age 85 reside in long-term care facilities, and institutionalization is an important risk factor for disordered sleep and for sedative hypnotic prescription. Consequently, the evaluation of any sedative hypnotic agent must include substantial assessment of efficacy, safety, and tolerance in geriatric patients.

Aged↗
PubMed1990

Compliant characteristics of single joints: preservation of equifinality with phasic reactions.

Electromyograms (EMGs) of elbow flexors and extensors, elbow joint angle and torque were recorded in healthy subjects in the "do not react voluntarily" paradigm. Random loading and unloading torque perturbations of different rise times (Tr) were applied. Perturbations with Tr less than 300 ms evoke a phasic increase (in case of loading) or decrease (in case of unloading) in the flexor EMGs. The shortest EMG latency of about 30 ms was observed with very rapid perturbations (Tr less or equal to 20 ms). Smooth torque changes (Tr of 500-800 ms) were not accompanied by noticeable phasic reactions. Two types of the compliant characteristics were recorded: those with a zone of relatively high stiffness at the starting point ("S-shaped" curves) and those with a relatively constant stiffness. The presence or absence of the S-shape does not depend on Tr and therefore, does not seem to depend on phasic reflex or triggered reactions. In some of the subjects who were tested twice with an intervals of 2 months, the form of the compliant characteristics changed. This finding suggests that presence or absence of the S-shape can depend upon the subject's ability to follow the "do not react voluntarily" instruction. The invariance of the compliant characteristics in the presence or absence of reflex reactions can be regarded as an example of equifinality in a case of transient perturbations generated within the motor control system.

Adult↗
PubMed1990

Using DSM-III criteria to diagnose delirium in elderly general medical patients.

Studies of delirium in general medical populations have used criteria for delirium different from current DSM-III or DSM-IIIR criteria of the American Psychiatric Association, or have used DSM-III or DSM-IIIR criteria without operationalizing the components of these criteria. Therefore this prospective study was conducted to establish an approach to operationalizing DSM-III criteria and to determine the incidence and prevalence of delirium. Two hundred thirty-five consecutive subjects age 70 and over admitted to general medicine underwent daily standardized screening. Patients with low scores on screening tests or clinical evidence suggestive of any psychiatric disorder and controls were seen by a psychiatrist, who determined whether delirium was present by applying explicit operational definitions to each component of the DSM-III criteria for delirium. We conclude that the syndrome of delirium as defined by the American Psychiatric Association is prevalent on admission among elderly on general medical services, but the number of cases developing in the hospital is much less than often stated in the literature.

Aged↗
PubMed1990

Organizing principles for single joint movements. III. Speed-insensitive strategy as a default.

1. Human subjects made discrete elbow flexions in a horizontal plane over different distances, from a stationary initial position to a visually defined stationary target 9 degrees wide. We measured joint angle, acceleration, and electromyograms (EMGs) from two agonist and two antagonist muscles. 2. Subjects made movements over four different distances following one of four different instructions. The first instructed the subject simply to choose a comfortable speed. The other three explicitly emphasized either speed, accuracy, or maintenance of the "same" speed over different distances. These instructions produced a wide range of movement velocities. 3. The initial rises of the acceleration (and therefore of the inertial torque), as well as the initial slope of the agonist EMG, were all invariant over changes in the target distance for any single instruction but were all sensitive to the given instruction. 4. Our results demonstrate that the speed-insensitive strategy is a standard or default pattern for performing movements that may be carried out for different instructions over a wide range of speeds. A uniform intensity of excitation pulse is not a byproduct of moving at maximal speed. Submaximal intensities are associated with submaximal speeds and are a selected feature of the pattern of movement control.

Acceleration↗
PubMed1990

Organizing principles for single-joint movements. IV. Implications for isometric contractions.

1. Normal human subjects made isometric pulse and step contractions about the elbow to visually defined target torques of different amplitudes and at different rates. We measured joint torque and electromyograms (EMG) from two agonist and two antagonist muscles. 2. When the task specification requires that the subject explicitly alter the rate at which torque is increased, the rates of rise of the agonist and antagonist EMG bursts covary with the rate of rise of the torque. For pulses of torque the duration of motoneuron excitation varies with the duration of the task-defined contractile event. 3. When a subject is asked to generate torques of different amplitudes without specifying a time interval, torque amplitude is positively correlated with how long, and therefore how high, the EMG rose. Subjects usually proportionately covary the strength of the agonist and antagonist contractions but are not constrained to do so. Some subjects use a strategy of varying the antagonist inversely with the agonist contraction. 4. We extend the organizing principles for the control of movement about a single joint to the control of isometric torque. These rules state that control of torque about a single joint is exercised by one of two strategies: the speed-sensitive strategy modulates the rate at which contraction rises by varying the intensity of motoneuron-pool excitation. The speed-insensitive strategy varies the duration over which contraction rises but does not change the rate. These two respective patterns of torque emerge from pulse-height and pulse-width modulation of motoneuron-pool excitation. 5. The rules defining speed-sensitive and speed-insensitive strategies for movements are broadened for isometric contractions because of the wider range of torque patterns that we observe under these conditions. We propose a step-excitation component for prolonged isometric step contractions and slowly rising ramp patterns of excitation for contractions that develop over several hundreds of milliseconds. 6. The choice of strategies is based on task-specific torque requirements. The same two strategies that control torque to produce movement apply to the control of isometric torque. Unlike movements, however, isometric tasks are more often controlled by a blending of the two patterns. Possible reasons for this are discussed.

Electromyography↗
PubMed1990

Effects of intrathecal baclofen on voluntary motor control in spastic paresis.

Intrathecal baclofen injections were given to six patients with long-standing spastic paresis resistant to any nondestructive treatment, including oral baclofen. Attempts by the patients at voluntary muscle activation before intrathecal administration of baclofen led to considerable uncontrolled coactivation of antagonist and distant muscles. After the injection, dramatic suppression of the spastic signs was accompanied by more selective voluntary muscle activation. Tonic coactivation of the antagonists and distant muscle groups during voluntary contractions was decreased while the agonist level on electromyography (EMG) was not affected (three cases) or only slightly reduced (three cases). Furthermore, in one patient with sufficient residual motor control function, there was a considerable increase in the speed of fast isotonic movements, accompanied by the emergence of the ability to generate phasic muscle bursts on EMG that were characteristic of normal motor patterns. The results suggest that baclofen exerts different effects upon reflex pathways and descending motor pathways. This therapy appears to be a promising way for improving residual motor control in patients with increased muscle tone and/or reflexes.

Baclofen↗
PubMed1990

Reflex responses to ankle perturbations during electrical stimulation of muscle: 1. Measurement techniques and preliminary examples.

Electrical stimulation of muscle has been proposed as a technique to restore function to paralyzed muscles. But, from a control stand-point, little is known about how such artificial activation interacts with the still intact spinal reflex loops. We have developed instrumentation to measure and compare ankle compliance and muscle EMG activity when the ankle is subjected to perturbations in torque or angular position from bias positions that are achieved volitionally or via electrical muscle stimulation. We deliver precise torque or position perturbations (step, ramp, sinusoidal, random) to the ankle via a pivoting footplate driven by a computer-controlled torque motor. Angular displacement, torque, acceleration, and 2 to 4 channels of electromyographic (EMG) data are collected on analog (VHS) tape and simultaneously digitized and stored. Torque or position biases to normal ankle equilibrium position are applied volitionally (for the neurologically intact) or via electrical stimulation of the Gastroc/Soleus or the Tibialis Anterior muscle (for either the neurologically intact or spinal cord injured). A special stimulator/recording amplifier permits the recording of EMG signals from the muscle being stimulated. An overview of the features and response characteristics of the perturbation system and a comparison from preliminary studies of responses at different biases achieved volitionally versus those achieved by stimulation are presented.

Ankle Joint↗
PubMed1979

Response to sudden torques about ankle in man: myotatic reflex.

1. Sudden dorsiflexions and plantarflexions of the foot were imposed on normal human subjects under various states of voluntary activity. 2. Under conditions of constant muscle contraction, the myotatic reflex in soleus and lateral gastrocnemius muscles is linearly and highly correlated with the rate of muscle stretch. The slope of this curve characterizes part of the reflex arc "gain." 3. The gain is linearly proportional to the level of tonic voluntary activation. 4. The gain is reduced by tonic contraction of antagonists. 5. The above statements can be summarized by the following equation (formula: see text), where d theta/dt is the rate of joint rotation. Ts and Tat are measures of voluntary contraction (tension) of all the extensor and flexor muscles acting at the ankle. The term S represents the level of preexisting spinal excitability that can be altered by prior instruction to the subject. 6. A phasic voluntary contraction of the soleus muscle, which leads to muscle shortening, will alter the reflex gain. The gain initially increases with increasing rates of shortening, but at higher rates the gain is reduced. This is in contradiction to the observation for tonic activation as stated above and may be due to an inability of the coactivated fusimotor system to produce sufficiently rapid cocontraction of the spindle fibers. 7. During lengthening of a muscle caused by voluntary contraction of its antagonists, the myotatic reflex gain is reduced. 8. The above facts are interpreted to imply that a functional role for the myotatic reflex in the leg extensors is limited to conditions of postural maintenance or slow, precise movement. During rapid movement, the myotatic reflex is ineffective and load-compensating reactions are mediated by longer latency loops. 9. The duration of the myotatic reflex EMG is from 10 to 40 ms, too brief to be a simple response to a velocity-sensing receptor organ. Either the response is in large measure due to the initial burst of spindle activity that occurs at the start of a ramp stretch, or motoneuron pool dynamics act as a high-pass filter on afferent inputs. 10. In the anterior tibial muscle, the relationships between stretch velocity and reflex amplitude and tonic voluntary contraction and reflex gain are qualitatively similar to those found in the ankle extensors.

Ankle↗
PubMed1978

Stretch and Hoffmann reflexes during phasic voluntary contractions of the human soleus muscle.

Measurements were made of EMG responses in human soleus muscle, following torque disturbances of the foot during phasic voluntary plantarflexions. These were compared with measurements of the Hoffmann reflex during identical voluntary movements. We observe that stretch adequate to evoke a stretch reflex in the relaxed limb often fails to evoke any response during a phasic contraction until about 120 msec after the onset of the stimulus. During this period the H-reflex is facilitated. These findings are discussed in terms of the servo-theory of stretch reflex function and the concept of trans-cortical stretch reflexes.

Adult↗