Biomedical subjects
Publications and source records attributed to E G Walsh.
Neurophysiologists have long been interested in phenomena associated with the activity of single nerve cells and much that has been found out has some implication for the management and understanding of spinal injuries. Others have been more concerned with integrative aspects, and it is with one aspect of this work that I am now concerned.
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Equinus in hemiplegic children is multifactorial. In some cases it is due to a short muscle, in others to simple foot-drop, tonic spasticity, rigidity, compensation for a short limb, fixed flexion contracture at the hip, dominantly inherited forefoot deformity, forefoot equinus secondary to chronic toe-walking, or abnormalities of the visco-elastic properties of the muscle, with true intramuscular contracture. This neurophysiological study confirms that hemiplegia in children is not a homogeneous condition. Some have tonic spasticity; some, although stiff, show electrical silence on stretching; some appear to have a short muscle, with no hypertonicity; and others have hypertonicity in relation to position (i.e. rigidity). A short muscle is not always associated with tonic spasticity with reciprocal inhibition. Weakness can occur without spasticity. Speed of movement of toes, ankle and hip is also significantly reduced.
The resonant frequency of the wrist has been measured in sixteen hypermobile and nine normal women at ten levels of peak torque. At the lowest level the results were identical but at the others the hypermobile values were lower. Damping and thixotropy appeared to be normal. In another group the grip strength of hypermobile subjects was similar to that of controls. The possibility that the connective tissue of the musculature of hypermobile subjects is of enhanced compliance is discussed.
Resting muscle tone of the leg was measured in terms of thigh muscle stiffness and knee resonant frequency in muscles of spinal cord injured subjects who had been involved in an electrical neuromuscular stimulation training programme of the thigh muscles over at least 2 months. The thigh circumference of these patients was 6.6% larger than before training commenced (P less than 0.001) and showed increased muscle stiffness and resonant frequency compared to a similar group of paralysed subjects who had not used any neuromuscular stimulation. Resonant frequency and stiffness after the long-term training were similar to those of non-injured controls and therefore the stimulation programme seemed to reverse the effects of paralysis on muscle tone. Short periods of rest (30 min) caused increased muscle stiffness in non-injured controls and paralysed muscles trained by neuromuscular stimulation. Additional 15 min periods of neuromuscular stimulation further increased muscle stiffness in the trained muscles but also in the muscles of paralysed subjects who had no long-term neuromuscular training. In contrast, 15 min sessions of passive movement of the knee decreased muscle stiffness in long-term trained paralysed muscles and untrained paralysed muscles. Knee resonant frequency was also significantly decreased in the trained paralysed muscles. Results show that muscle tone varies depending on the amount of previous movement or rest and that although neuromuscular stimulation of paralysed muscles increases muscle stiffness and knee resonant frequency, it is in fact restoring such properties of the muscle to a state approaching that of non-injured controls.
The thermogenic beta 3-adrenoceptor agonist BRL 26830A has been shown to increase weight loss in dieting subjects but tremor was a frequent adverse effect. We have investigated the magnitude and nature of this tremor after a single oral dose in 18 subjects. Two complementary techniques were used to attach the recording apparatus to the subjects to give both isotonic and isometric measures of tremor. Increases of 84% and 40% respectively were found due to exaggeration of physiological tremor presumably mediated through concomitant beta 2-adrenoceptor stimulation. The use of beta 3-adrenoceptor agonist drugs in the treatment of obesity may increase but the development of an agent without tremor inducing properties would be an obvious advantage.
The biodynamics of the feet of spastic children have been studied by estimating the resonant frequency using a printed motor to supply rhythmic torques. Changes induced when the muscles have been stretched by casting for four weeks are trivial or absent. The position of the feet, however, after the procedure became more nearly normal.
The thigh muscle tone of non-injured subjects and complete injury paraplegics has been investigated using torques, generated by a printed motor, to move the knee. The dynamic measure of resonant frequency (related to stiffness) together with a static measure of stiffness have shown the legs of non-injured subjects to respond non-linearly to decreasing torques. However, the complete paraplegics' legs did not respond non-linearly but showed constant resonant frequency and stiffness over the range of torques. Peak velocity at resonance (inversely related to damping) gradually increased with increasing torques in both groups. In addition, at a chosen baseline torque of 0.7 N m, resonant frequency and muscle stiffness were significantly lower and peak velocity significantly higher in the paraplegics compared to the non-injured subjects. Contrary to expectations the thigh muscles in established, complete paraplegia showed a lack of tonic EMG activity. In addition, whilst phasic stretch responses were occasionally seen there was no tonic activity in relation to continued stretch. Since muscles atrophy after paralysis, the smaller muscle bulk may contribute to the lower muscle tone.
The wrist has been moved rhythmically in the horizontal plane by sinusoidal torques provided by a printed motor. Measurements have been made on normal subjects and subjects with rheumatoid arthritis. Both groups exhibited a resonance, the oscillations being greatest when the applied torque was of certain frequency. In both groups the resonant frequency fell to approximately the same constant value when the torque was raised. While the main relationships were similar a somewhat lower torque resulted in the lowering of resonant frequency in the patients. The relationship between applied torque and peak velocity at resonance was also studied. For a given torque the motion was greater in the patients. No objective signs of increased viscous or elastic stiffness were demonstrable at the wrist in patients with rheumatoid arthritis.
Rhythmic forces have been applied to the wrist of patients with Parkinsonism tremor by means of a printed motor. The tremor rate was not altered to that of the applied force. On the contrary, beats were established, the rate of which depended on the difference in rate between the tremor and the applied rhythm. Most of the observations have been for horizontal motion of the hand but similar phenomena have been seen for vertical movements, and for other parts of the body--for example, foot, elbow, finger joint, and head. The observations are regarded as supporting the view that the tremorgenic mechanism is central. There was no electromyographic evidence of servo driving or servo assistance in the genesis of the tremor.
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(1) Clonus has been elicited by using a printed motor in nine patients with sustained ankle clonus. (2) When a dorsiflexing biasing force was applied to the foot the amplitude, but not the frequency, of the clonus varied according to the strength of the force. (3) When the biasing force was withdrawn there could be, for some seconds, continuing EMG evidence of a rhythmic discharge. (4) The clonus did not synchronise with an externally applied rhythmic force. In all relevant observations beats were set up between the clonus and the applied force. (5) When clonus was started by the abrupt application of bias the waveform in successive trials was fairly closely repeatable. (6) Beats were also established in two cases of wrist clonus. (7) It is concluded that clonus is not due to the self re-excitation of proprioceptive reflexes but is dependent on a spinal generator, the rate of beating of which is normally independent of peripheral circumstances, although it may be switched on and its activity maintained by appropriate events.
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