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At least 487 records · Page 27Linked to original sources
PubMed1998

Stretch reflex sensitivity: effects of postural and muscle length changes.

In this study, a combination of clinical evaluation, laboratory testing, and model simulation of spasticity is performed under various postural conditions to investigate the changes in the sensitivity and specific mechanisms of spasticity. Fifty-nine multiple sclerosis patients participated in the study and received spasticity evaluation based on both the Ashworth scale and the pendulum test. Spasticity was found to increase in the pendulum test when the subjects were tested in a supine posture, compared to when they were sitting. Three patterns of stretch reflex response were seen for similar leg swing trajectories. While it was clear that the increased stretch of rectus femoris in the supine posture contributed to the increased spasticity, the results of modeling showed that other more complex factors were also involved. The supraspinal descending modulation associated with postural control may play a more dominant role in the severity of spasticity. The results suggest that the biomechanical test of spasticity should be performed for several different postures or ranges of movement with muscle activities monitored simultaneously, so that the effect of various factors can be examined. The work also indicates that a neuromusculoskeletal model with detailed muscle dynamics and stretch reflex loops is a valuable tool for investigating the neural mechanisms of spasticity.

Adult↗
PubMed2001

Analysis of the reflexive feedback control loop during posture maintenance.

In previous work it has been shown in posture experiments of the human arm that reflexive dynamics were substantial for narrow-band stochastic force disturbances. The estimated reflex gains varied substantially with the frequency content of the disturbances. The present study analyses a simplified linear model of the reflexive feedback control loop, to provide an explanation for the observed behaviour. The model describes co-activation and reflexive feedback. The task instruction 'minimize the displacements' is represented mathematically by a cost function that is minimized by adjusting the parameters of the model. Small-amplitude displacements allow the system to be analysed with a quasilinear approach. The optimization results clarify the limited effectiveness of reflexive feedback on the system's closed-loop behaviour, which emanates from the time delay present in the reflex loops. For low-frequency inputs less than 5 Hz, boundary-stable solutions with high reflex gains are predicted to be optimal. Input frequencies near the system's eigenfrequency (about 5 Hz), however, would be amplified and result in oscillatory behaviour. As long as the disturbance does not excite these frequencies, boundary stability will be optimal. The predicted reflex gains show a striking similarity with the estimated reflex gains from the experimental study. The present model analysis also provides a clear explanation for the negative reflex gains, estimated for near-sinusoidal inputs beyond 1.5 Hz.

Feedback↗
PubMed2001

Effect of sensory inputs alteration and central sensory disinteraction on postural sway and optokinetic reflex maintaining simultaneously body balance.

We aimed at estimating the effect of central sensory disinteraction on postural sway (PS) and optokinetic reflex (OKR) maintaining concurrently body balance. Healthy humans (N) and patients (P) with multiple sclerosis, and undergone infarct in the middle cerebral artery were examined. They stood on stable platform and foam rubber under three conditions: eyes open; eyes closed; during horizontal central optokinetic stimulation (COKS). On stable platform, a difference between PS of N and P was not found, while on foam rubber, PS of P was significantly greater than PS of N. During COKS on stable platform, PS increased only in P, while on foam rubber it increased in both N and P. OKR gain of N was circa 1 on stable and unstable supports, while that of P was 0.5. We concluded that artificial sensory disinteraction causes strong postural instability, but does not affect OKR.

Adult↗
PubMedDate not supplied

Techniques to measure pharmacodynamics in the intact vasculature.

Techniques are described for the intravenous, close intraarterial, or perivascular delivery of drugs in conscious or anaesthetized animals. Examples of the determination of pharmacodynamic parameters such as regional blood flow, large artery diameter, resistance, conductance, and blood pressure are given for conscious rabbits and anaesthetized dog preparations. An important issue is how to determine the direct vascular action of an injected drug in the light of rapid and powerful autonomic reflex buffering effects especially in healthy conscious animals. The methods of measurement of drug action on the baroreceptor-heart rate reflex and postural adaptation (90 degrees tilt) reflex in the conscious rabbit are explained. Finally, the changes to large and small artery morphology are explored in the rabbit hindlimb following conduit femoral artery ligation to induce arteriogenesis and angiogenesis. This work aims to highlight approaches to exploring drug action in vivo, a much neglected skill in the repertoire of the modern cardiovascular pharmacologist.

Animals↗
PubMedDate not supplied

Procedure for assessment of neurodevelopmental delay in young children: preliminary report.

This report describes the development of a new procedure for assessing neurodevelopmental delay in young children. The Primitive Reflex and Postural Adjustment Assessment procedure is designed to measure degrees of occurrence of remnants of primitive reflexes and immature postural adjustment. Preliminary findings show that the Primitive Reflex and Postural Adjustment Assessment procedure can successfully identify degrees of neurodevelopmental delay in young children, and that the procedure differentiates normal children from mentally retarded and emotionally disturbed children. Additional work is needed to assess the validity and reliability of this procedure.

Affective Symptoms↗
PubMedDate not supplied

Volume displacement of the tympanic membrane at stapedius reflex activity in different postures. Studies on variations in perilymphatic pressure.

With the microflow method the volume displacement of the tympanic membrane and its direction of movement can be recorded at stapedius reflex contraction. There is an outward or inward movement of the tympanic membrane, which is affected by changes in posture. The results indicate that the perilymphatic pressure in man varies with the posture and that these variations can be measured indirectly outside the tympanic membrane. This can only be done, however, on condition that there are no pressure variations across the tympanic membrane. This method opens up new ways of studying possible pressure changes in the inner ear in acute diseases.

Auditory Threshold↗
PubMed2004

Responsiveness of the H reflex to loading and posture in patients following stroke.

The objective of the research was to examine the effects of loading and posture on motoneuronal excitability of the triceps surae (TS) for patients with hemiplegia. Twelve healthy subjects and 12 patient subjects with post-stroke hemiparesis (onset period: 3-60 months) were enrolled in this study. The subjects were instructed to remain in quiet sitting with the test knee straight and three standing conditions of different superincumbent loads by shifting body weight to the test leg (10%, 50%, and 90% of body weight), while the H reflexes and M waves of the TS were measured. The results clearly indicated that H reflex amplitudes were not affected by different loading conditions in standing for both healthy subjects and patients who had a previous stroke. In addition, the H reflex amplitude in quiet standing for healthy subjects was significantly downward modulated relative to that in relaxed sitting with the test knee straight, but this posturally driven modulation was impaired in patients following stroke. Current electrophysiological findings imply that body weight as a means for rehabilitation facilitation had little immediate effect on paretic TS, and absence in postural gating of reflex excitability appeared to be an incentive for postural instability resulting from post-stroke hemiparesis.

Adult↗
PubMed1992

Positioning of the stroke patient: a review of the literature.

Stroke is a common and disabling illness, adversely affecting the quality of life of hundreds of people each year. While there are many therapeutic approaches to stroke patient rehabilitation, encouraging patients to adopt "reflex-inhibiting" patterns of posture is a widely advocated strategy for helping patients to avoid complications of hemiplegia such as spasticity and contractures. However, while the central role of nurses in thus helping patients is recognized, the influence of posture on recovery from stroke has never been evaluated. Prior to undertaking such an evaluative study, texts on stroke patient care were reviewed to clarify the received view about the recommended positioning for patients with hemiplegia. Consensus on some issues was evident (such as positioning the patient with the affected shoulder protracted, spine straight, fingers extended and avoiding external rotation of the affected hip). However, opinion was divided on others and a number of potentially important aspects were ill-covered. This paper integrates a summary of the findings of this review with the physiological rationale for the recommendations. The main areas of agreement are highlighted and issues as yet unanswered are raised for further consideration.

Cerebrovascular Disorders↗
PubMed1979

Comparison of three positions for evaluating the asymmetrical tonic neck reflex.

Twenty-four males ages 8 to 11 were videotaped while being tested in three positions for the ATNR: quadruped with the head passively rotated to either side; standing with the arms outstretched and eyes closed with the head passively rotated to either side; and quadruped reflex inhibiting posture with the skull hand on the hip and the face knee off the floor and with the head actively rotated to either side. Three "expert" raters viewed the edited tape and rated each subject in each position using a protocol devised for the study. The results suggest that the quadruped reflex inhibiting posture more readily reveals the presence of the reflex when compared to the other positions, in this population of learning-disabled children.

Child↗
PubMed1991

The effect of posture on the normal and pathological auditory startle reflex.

The effect of posture on the EMG pattern of the normal auditory startle reflex was investigated. The startle response to an unexpected auditory tone was studied in eleven normal subjects when standing, and in six normal subjects when sitting relaxed or tonically plantar flexing both feet. Reflex EMG activity was recorded in the tibialis anterior and soleus about twice as frequently when standing, than when sitting relaxed. In addition, the median latencies to onset of reflex EMG activity in the tibialis anterior and soleus were about 40 and 60 ms shorter during standing, than when sitting relaxed. No short latency EMG activity was recorded in the calf muscles during tonic plantar flexion of the feet, while sitting. The effect of posture on the EMG pattern of the pathological auditory startle reflex was studied in five patients with hyperekplexia. In three patients the latency to onset of reflex EMG activity in the tibialis anterior was shorter when standing, than when sitting relaxed. The EMG pattern of the reflex response to sound was studied in detail in two of these patients and consisted of up to three successive components. The expression of each EMG component depended on the postural set of the limbs. In particular, a distinct short latency component was found in posturally important muscles following auditory stimulation. This short latency component was not recorded when sitting relaxed. It is concluded that the EMG pattern of the physiological and pathological auditory startle response is not fixed, but may change with the postural stance of the body. This finding supports the theory that the normal startle reflex and the abnormal startle reflex in hyperekplexia have a common brainstem origin.

Adolescent↗