Spastic Subjects Research Articles

A quantitative analysis of pendular motion of the lower leg in spastic human subjects

The purpose of this study was to examine gravity-induced oscillations of the lower leg in normal and spastic subjects, with a view towards evaluating a clinical test of spasticity called the "pendulum" test. Motivations for studying the pendulum test were to determine if realistic aspects of spasticity and neuromuscular control could be incorporated into a description of the motion, and to better understand the underlying neurophysiological disturbances in spasticity. For passive limb motion (in which no reflex excitation occurred), a second-order linear model did not provide an adequate description of the motion for either spastic or normal legs. Instead, system equations including nonlinear mechanical properties simulating asymmetries in the swing and amplitude dependent variations in stiffness and damping provided a more accurate description. For spastic limb motion (in which reflex excitation did occur), accurate simulation required components accounting for abnormal reflex activation, coinciding with the time course of EMG activation. These included increased stiffness and damping with their gains related to reflex EMG magnitude, and changes in the rest length of the stiffness. Comparison of numerical solutions of the equations with experimental data showed our nonlinear model simulated the motion accurately, with the variance accounted for usually exceeding 90%.

Cumulative vibratory indices and the H/M ratio of the soleus H-reflex: a quantitative study in control and spastic subjects

Suppression of the soleus (Sol) H-reflex recruitment curve by Achilles tendon vibration and the ratio of maximum Sol H-reflex (H max) to maximum M-response (H/M ratio) have been studied by means of computer processing on the basis of peak-to-peak (P-P) and area values in 46 controls and in 16 spastic patients. The ‘classical’ vibratory index (VI) has been compared with a new cumulative VI (CVI), which is defined as the quotient of the surface under the recruitment curve obtained with vibration and the one obtained without vibration up to an equal intensity level. Statistical analyses were performed from threshold to 3 different intensity levels. Tendon vibration is found to be less effective at higher intensity levels. Mean values with S.D.s of CVIs at H max intensity are significantly lower than those of the ‘classical’ VIs. VIs increase with age while H/M ratios decline. Stepwise discriminant analyses showed that area CVI at H max intensity yielded the best distinction between controls and patients. Additional differential contribution is obtained by P-P H/M ratio. A canonic variable derived from these two variables correctly classified 44 out of 46 controls and 15 out of 16 patients. The methods presented improve the specificity of the quantitative neurophysiological measure of spasticity by means of Sol H-reflex recordings.

Spasticity: Quantitative Measurements as a Basis for Assessing Effectiveness of Therapeutic Intervention

Spasticity, a common problem in upper motor neuron lesions, frequently results in uncontrolled involuntary motion that interferes with function. A quantifiable method related to the mechanical output of the muscle is needed to test and improve therapeutic intervention. A sinusoidal displacement of 5 degrees was used to measure elastic and viscous stiffness around the ankle at frequencies from 3 to 12Hz. To isolate viscoelastic response, the influences of inertia and equipment drag were eliminated. Test-retest correlation values were 0.953 for elastic and 0.992 for viscous stiffness. The elastic stiffness in 13 spastic subjects under nerve block was significantly higher than that of 13 healthy subjects (p less than or equal to 0.05), indicating early changes associated with contracture. Elastic and viscous response is expressed by the total stiffness vector containing both components, the Nyquist diagram. This diagram's pathlength from 3 to 12Hz was calculated and showed high test-retest reliability in healthy subjects. The median pathlength value for the spastic group was 98 Newton-meters/radian (N-m/rad) and, for the normal group, 24N-m/rad, a statistically significant difference (p less than or equal to 0.0001). A mathematical model of the spastic response shows that the Nyquist diagram's pathlength relates to reflex loop gain and is independent of the shift in passive properties. The model predicts a shift in passive properties during spastic responses relative to responses measured during nerve block. Thus, subtraction of passive responses measured during nerve block may not isolate the remaining reflex response, but the pathlength measure relating to the reflex response gain was unaffected, allowing evaluation of therapeutic intervention effectiveness.

Laumbosacral Somatosensory Evoked Potentials in Spastic Spinal Cord Injury Patients and Healthy Subjects

Laumbosacral Somatosensory Evoked Potentials in Spastic Spinal Cord Injury Patients and Healthy Subjects

Quantitative relations between hypertonia and stretch reflex threshold in spastic hemiparesis.

The relative contributions of variations in stretch reflex threshold and total joint stiffness to changes in stretch-evoked torque were assessed in the spastic elbow muscles of 14 hemiparetic spastic subjects. For a given subject, variations in torque, measured after a constant angular deflection, were mediated largely by changes in stretch reflex threshold, rather than by changes in reflex stiffness. Between-subject comparisons were sensitive to stiffness differences between limbs, but reflex thresholds were still broadly correlated with torque magnitude, suggesting that reductions in stretch reflex threshold are uniformly present in spastic muscles. These findings, coupled with the apparent similarity of reflex stiffness estimates in voluntarily activated spastic and normal muscles, suggest that the central disturbance in spasticity is a reduction in the threshold of the stretch reflex, without a significant enhancement of reflex gain.

Perturbation of a skilled action 2. normalising the responses of cerebral palsied individuals

Subjects were trained to execute a radial elbow extension of prescribed arc and velocity profile. A DC servomotor was used to introduced brief perturbations, opposing extension. Neurologically normal and cerebral palsied subjects' reactions to a range of perturbation magnitudes were tested. The training stage of the study was designed to provide cerebral palsied subects with an electromyographic target profile of how to respond to a given perturbation,modelled on the performances of neurologically normal subjects, but taking account of individual differences in how non-perturbed arm swings were executed electromyographically. In the event, spastic subjects were not hyperreactive to perturbations when tested. A follow-up study confirmed the interpretation that this was a consequence of learning to perform the test arm swing with stringent precision. The implications of the study for models of spasticity and prospects for rehabilitation are discussed.

Voluntary muscle release is not accompanied by H-reflex inhibition in patients with upper moto neuron lesions

Changes in excitability of the soleus (Sol) monosynaptic reflex are were investigated in spastic subjects, affected by amyotrophic lateral sclerosis (ALS), upon voluntary relaxation of tonic contraction of triceps surae muscle. Force and electromyograms (EMG) were recorded during triceps release, performed in response to an acoustic signal, in a reaction-time (RT) situation. Sol H-reflex was evoked at random during the task, and its amplitude was referred in time to the end of Sol EMG. At variance with the results for the same task in normal subjects, it was found that in ALS patients the RTs of the termination of EMG were longer than those of the beginning of the EMG, the decrease in force was prolonged and perturbed owing to intercurrent clonus-like EMG activity, and the H-reflex did not undergo the expected profound inhibition. It is suggested that the absence of the activation of presynaptic inhibitory mechanisms by the descending command to release brings about major disorders in voluntary muscle relaxation.

Modification of spastic gait through mechanical damping

The effect of dissipative mechanical loads on spastic gait has been studied, to evaluate the feasibility of using mechanically damped orthoses to effect functional improvements in the gait of spastic patients. This concept is based on a hypothesis citing uninhibited, velocity-dependent stretch reflexes as a possible causal factor in spastic gait abnormalities, such as equinus and back-kneeing. In order to screen potential experimental subjects and to quantify velocity-dependent reflex behaviour, ankle rotation experiments and filmed gait analysis were performed. The results supported the existence of a velocity threshold. Orthosis simulation experiments were performed with one spastic subject, using a wearable, computer-controlled, electromechanical, below-knee orthosis simulator to apply a variety of damping loads to the ankle as the subject walked. Results indicated that appropriate damping can improve local joint kinematics. The damping causes a reduction in muscle stretch velocity which apparently results in reduced spastic reflex activity.

The ankle stretch reflexes in normal and spastic subjects. The response to sinusoidal movement.

Forces and electromyograms were recorded during sinusoidal flexion-extension movements of normal and spastic ankle joints. Spastic subjects showed relatively stereotyped responses, with evidence of a vigorous spinal stretch reflex. The responses of normal limbs were variable; there was little reflex response to the first cycles, but as the movement continued the reflex responses increased and often came to resemble the responses of spastic limbs. At some frequency between 3 and 7 Hz, the reflex response was so timed that it tended to assist rather than resist the movement; this was the frequency at which many subjects (normal, as well as spastic) exhibited spontaneous clonus if an appropriate load was attached to the foot. The frequency of this clonus changed with changes of load. It is concluded that whereas the gain of a normal stretch reflex may vary considerably, the stretch reflex of the spastic subject is set at one end of the normal range. With this high gain, the stretch reflex may support spontaneous clonus in both normal and spastic subjects.

Dysarthria of adult cerebral palsy: I. Intelligibility and articulatory impairment.

The speech intelligibility and articulatory impairment of 32 spastic and 18 athetoid males, aged 17-55, were examined. Selection was based on a definite diagnosis of cerebral palsy, and adequate intelligence, hearing, and ability to perform the required tasks. Two estimates of speech intelligibility were obtained from naive listeners: single words correctly recognized and prose intelligibility rating. Diadochokinetic (DDK) syllable rates and percent correct articulation of selected phonemes were employed as indices of articulatory impairment. The 50 subjects were, on average, judged to be 50% intelligible on both intelligibility estimates. Group mean DDK rate was 2.9 syllables per second and 78% of phonemes were transcribed as correctly articulated. :The mean scores of the spastic subjects were superior to the athetoids on all speech measures, significantly so for single-word intelligibility and DDK rate even when group inequalities for physical disability and I.Q. were adjusted. In this sample, spastics were less physically disabled and had lower I.Q.'s than athetoids. Specific phonemic features characteristic of the dysarthria in cerebral-palsied subjects were: (1) anterior lingual place inaccuracy; (2) reduced precision of fricative and affricate manners; and (3) inability to achieve the extreme positions in the vowel articulatory space. A comparison of these results with those reported for children with cerebral palsy suggests that the consonantal place and manner problems are fairly stable features of cerebral palsy dysarthria.

Tonic stretch reflexes in lip, tongue and jaw muscles

Despite considerable speculation it remains unclear as to whether stretch reflexes perform a functional role in speech articulator muscles. Recent research, however, has shown that long loop stretch reflex mechanisms are brought into play during voluntary contraction of limb muscles and a functional role in oscillatory damping has been suggested. It was decided, therefore, to use a method and a technique of analysis similar to that used in limb muscles to search for tonic stretch reflex (TSR responses in lip, tongue and jaw muscles during sustained voluntary contraction. The term ‘action TSR’ is used to differentiate stretch reflex responses measured during voluntary activity from those measured at rest. Simultaneous electromyogram (EMG) recordings were taken from the lip, tongue and jaw musculature in normal, stutterer and cerebral spastic subjects. Subjects were instructed to hold the appropriate articulator in a fixed position while the experimenter applied an irregular, continuously changing, stretching force. The stretch and EMG signals were analyzed using a cross correlation and spectral analysis technique. This provided a sensitive means of detecting any EMG fluctuations which covaried with applied stretch and might therefore be classified as reflex. No suggestion of such action TSR responses could be found in lip or tongue muscles of any of the subjects tested, including the cerebral spastic subjects with dysarthric speech. It is therefore concluded that action TSR mechanisms are not operative in control of lip and tongue muscles in man. Furthermore, dysarthric speech in cerebral spasticity cannot be attributed to exaggerated tone of lip and tongue muscles resulting from hypersensitivity of TSR mechanisms. In contrast, clear action TSR responses were demonstrable in jaw closing muscles while in jaw opening muscles, small amplitude responses were detected but were not substantial in comparison with background activity. Since the action TSR is present in jaw and limb muscles, but absent in lip and tongue muscles, the suggestion of a functional role of this reflex in damping mechanical oscillations associated with inertial loads is further supported.

The ‘late’ electromyographic response to limb displacement in man. I. Evidence for supraspinal contribution

Recent findings in primate experiments suggest that the ‘late’ EMG response (termed here the FSR) to sudden limb displacement, generated with the intention to oppose the stimulus, might be mediated via a transcortical long-loop pathway. In the present investigation we tested this hypothesis in man by examining the EMG responses elicited in a variety of limb muscles in opposition to sudden limb displacements. These were generated either by a manually applied force or by means of a servo-controlled high performance electro-hydraulic actuator. Ten normal human subjects and 22 with clinically established spasticity (12 with a high probability of mid-thoracic transection, 10 with cerebral lesions) were studied. In normal subjects, the difference between tendon jerk and FSR latencies was found to increase with descending spinal level of muscle innervation, being 32.1, 47.2 and 73.1 msec respectively for biceps, quadriceps and gastrocnemius. Provided that this measure reflects the time required for central conduction, this finding is compatible with the long-loop hypothesis. Furthermore, no EMG response was ever observed in the affected muscles of the spastic subjects in the time bracket normally occupied by the FSR, despite the fact that the tendon jerk response was present and prolonged. This suggests that the segmental mechanisms responsible for hyper-reflexia cannot themselves generate the FSR. It is therefore concluded that the results are consistent with the current view that a long-loop pathway, probably involving the cortex, contributes to the FSR in response to sustained stretch in man.

Spread of phasic muscle reflexes in normal and spastic subjects

Spread of phasic muscle reflexes in normal and spastic subjects

Electro‐Encephalographic Examinations of Imbeciles.

Summary.42 imbeciles (20 mongoloids and 22 spastic subjects) were examined with electro‐encephalograms. Regular alpha frequency was recorded in 11 mongoloids and 10 spastic subjects, irregular and sparse alpha waves in 4 mongoloids and 4 spastic subjectsThe alpha waves appeared more sporadically and in shorter periods in the spastic subjects and mongoloids as compared with the normal cases. In all cases of regular alpha frequency, a lower frequency was found in the mongoloids than in the spastic subjects, with a single exception. The results in the cases with alpha‐like, irregular waves correspond with the typical casesThe alpha frequency in all the mongoloids with a low intelligence quotient was far below the normal values for the age, whereas the alpha frequency in all the spastic subjects, even in those with a very low intelligence quotient, fell within, or in the neighbourhood of, the normal limits of variation for the age.